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Title: Creation of the Teton Landscape: The Geologic Story of Grand Teton
National Park

Author: J. D. Love
John C. Reed

Release date: August 18, 2016 [eBook #52838]
Most recently updated: October 23, 2024

Language: English

Other information and formats: www.gutenberg.org/ebooks/52838

Credits: Produced by Stephen Hutcheson, Dave Morgan and the Online
Distributed Proofreading Team at http://www.pgdp.net

*** START OF THE PROJECT GUTENBERG EBOOK CREATION OF THE
TETON LANDSCAPE: THE GEOLOGIC STORY OF GRAND TETON
NATIONAL PARK ***

View west toward Grand Teton on skyline. Hedrick’s Pond surrounded by “knob and kettle”
topography is in foreground, tree-covered Burned Ridge moraine is in middle distance, and
extending from it to foot of mountains is gray flat treeless glacial outwash plain. National
Park Service photo by W. E. Dilley.

View west up Cascade Canyon, with north face of Mt. Owen in center. National Park Service
photo by H. D. Pownall.

To Fritiof M. Fryxell, geologist, teacher,
writer, mountaineer, and the first ranger-naturalist
in Grand Teton National Park.
All who love and strive to understand
the Teton landscape follow in his footsteps.

CREATION OF THE
TETON LANDSCAPE
The Geologic Story of
Grand Teton National Park
By
J. D. LOVE AND JOHN C. REED, JR.
U.S. Geological Survey

Library of Congress Catalogue Card No.: 68-20628
ISBN O-931895-08-1

1st Edition
1968

1st Revised Edition
1971

Reprinted 1979
Reprinted 1984
Reprinted 1989

Grand Teton Natural History Association
Moose, Wyoming 83012

4

CONTENTS
Foreword 6

THE STORY BEGINS 8
First questions, brief answers 9
An extraordinary story 10
An astronaut’s view 12
A pilot’s view 14
A motorist’s view 15
View north 15
View west 18
View south 19
A mountaineer’s view 20

CARVING THE RUGGED PEAKS 24
Steep mountain slopes—the perpetual battleground 24
Rock disintegration and gravitational movement 24
Running water cuts and carries 26
Glaciers scour and transport 28
Effects on Jackson Hole 30

MOUNTAIN UPLIFT 36
Kinds of mountains 36
Anatomy of faults 38
Time and rate of uplift 40
Why are mountains here? 41
The restless land 43

ENORMOUS TIME AND DYNAMIC EARTH 45
Framework of time 45
Rocks and relative age 45
Fossils and geologic time 46
Radioactive clocks 47
The yardstick of geologic time 48

PRECAMBRIAN ROCKS—THE CORE OF THE TETONS 51

Ancient gneisses and schists 51
Granite and pegmatite 55
Black dikes 58
Quartzite 63
A backward glance 64
The close of the Precambrian—end of the beginning 64

THE PALEOZOIC ERA—TIME OF LONG-VANISHED SEAS AND THE
DEVELOPMENT OF LIFE
66
The Paleozoic sequence 66
Alaska Basin—site of an outstanding rock and fossil record 66
Advance and retreat of Cambrian seas; an example 69
Younger Paleozoic formations 74

THE MESOZOIC—ERA OF TRANSITION 79
Colorful first Mesozoic strata 79
Drab Cretaceous strata 81
Birth of the Rocky Mountains 82

TERTIARY—TIME OF MAMMALS, MOUNTAINS, LAKES, AND
VOLCANOES
86
Rise and burial of mountains 88
The first big lake 92
Development of mammals 95
Volcanoes 98

QUATERNARY—TIME OF ICE, MORE LAKES, AND CONTINUED
CRUSTAL DISTURBANCE
102
Hoback normal fault 103
Volcanic activity 103
Preglacial lakes 104
The Ice Age 105
Modern glaciers 112

THE PRESENT AND THE FUTURE 113

APPENDIX 115
Acknowledgements 115

Selected references—if you wish to read further 116
About the authors 117
Index of selected terms and features 118

6

FOREWORD
Geology is the science of the Earth—the study of the forces, processes, and past
life that not only shape our land but influence our daily lives and our Nation’s
welfare. This booklet, prepared by two members of the U.S. Geological Survey,
discusses how geologic phenomena are responsible for the magnificent scenery
of the Teton region.

Recognition of the complex geologic history of our Earth is vital to the
enjoyment and appreciation of beautiful landscapes and other natural wonders, to
the planning of our cities and highway systems, to the wise use of our water
supplies, to the study of earthquake and landslide areas, to the never-ending
search for new mineral deposits, and to the conservation and development of our
known natural resources. Who can say, in the long run, which of the many uses of
this knowledge is the most compelling reason to seek an understanding of the
Earth?

W. T. Pecora, Director
U.S. Geological Survey
This booklet is based on geologic investigations by the
U. S. Geological Survey in cooperation with the National Park Service,
U. S. Department of Interior.

“Something hidden. Go and find it. 7

Go and look behind the Ranges—
Something lost behind the Ranges.
Lost and waiting for you. Go.”

KIPLING—THE EXPLORER

8

THE STORY BEGINS
The Teton Range is one of the most magnificent mountain ranges on the North
American Continent. Others are longer, wider, and higher, but few can rival the
breath-taking alpine grandeur of the eastern front of the Tetons. Ridge after
jagged ridge of naked rock soar upward into the western sky, culminating in the
towering cluster of peaks to which the early French voyageurs gave the name “les
Trois Tetons” (the three breasts). The range hangs like a great stone wave poised
to break across the valley at its base. To the south and east are lesser mountains,
interesting and scenic but lacking the magic appeal of the Tetons.

This is a range of many moods and colors: stark and austere in morning sun, but
gold and purple and black in the softly lengthening shadows of afternoon; somber
and foreboding when the peaks wrap themselves in the tattered clouds of an
approaching storm, but tranquil and ethereal blue and silver beneath a full moon.

These great peaks and much of the floor of the valley to the east, Jackson Hole (a
hole was the term used by pioneer explorers and mountain men to describe any
open valley encircled by mountains), lie within Grand Teton National Park,
protected and preserved for the enjoyment of present and future generations.
Each year more than 3 million visitors come to the park. Many pause briefly and
pass on. Others stay to explore its trails, fish its streams, study the plants and
wildlife that abound within its borders, or to savor the colorful human history of
this area.

Most visitors, whatever their interests and activities, are probably first attracted to
the park by its unsurpassed mountain scenery. The jagged panorama of the Tetons
is the backdrop to which they may turn again and again, asking questions,
seeking answers. How did the mountains form? How long have they towered into
the clouds, washed by rain, riven by frost, swept by wind and snow? What
enormous forces brought them forth and raised them skyward? What stories 9
are chronicled in their rocks, what epics chiseled in the craggy visage of this
mountain landscape? Why are the Tetons different from other mountains?

First questions, brief answers

How did the Tetons and Jackson Hole form? They are both tilted blocks of the
earth’s crust that behaved like two adjoining giant trapdoors hinged so that they
would swing in opposite directions. The block on the west, which forms the
Teton Range, was hinged along the Idaho-Wyoming State line; the eastern edge
was uplifted along a fault (a fracture along which displacement has occurred).
This is why the highest peaks and steepest faces are near the east margin of the
range. The hinge line of the eastern block, which forms Jackson Hole, was in the
highlands to the east. The western edge of the block is downdropped along the
fault at the base of the Teton Range. As a consequence, the floor of Jackson Hole
tilts westward toward the Tetons (see cross section inside back cover).

When did the Tetons and Jackson Hole develop the spectacular scenery we see
today? The Tetons are the youngest of all the mountain ranges in the Rocky
Mountain chain. Most other mountains in the region are at least 50 million years
old but the Tetons are less than 10 million and are still rising. Jackson Hole is of
the same age and is still sinking. The Teton landscape is the product of many
earth processes, the most recent of which is cutting by water and ice. Within the
last 15,000 years, ice sculpturing of peaks and canyons and impounding of glacial
lakes have added finishing touches to the scenic beauty.

Why did the Tetons rise and Jackson Hole sink? For thousands of years men have
wondered about the origin of mountains and their speculations have filled many
books. Two of the more popular theories are: (1) continental drift (such as South
America moving away from Africa), with the upper lighter layer of the earth’s
crust moving over the lower denser layer and wrinkling along belts of weakness;
and (2) convection currents within the earth, caused by heat transfer, resulting in
linear zones of wrinkling, uplift, and collapse.

These concepts were developed to explain the origin of mountainous areas 10
hundreds or thousands of miles long but they do not answer directly the
question of why the Tetons rose and Jackson Hole sank. As is discussed in the
chapter on mountains, it is probable that semifluid rock far below the surface of
Jackson Hole flowed north into the Yellowstone Volcanic Plateau-Absaroka
Range volcanic area, perhaps taking the place of the enormous amount of ash and
lava blown out of volcanoes during the last 50 million years. The origin of the
line of weakness that marks the Teton fault along the east face of the Teton Range
may go back to some unknown inequality in the earth’s composition several

billion years ago. Why it suddenly became active late in the earth’s history is an
unanswered question.

The ultimate source of heat and energy that caused the mountains and basins to
form probably is disintegration of radioactive materials deep within the earth.
The Tetons are a spectacular demonstration that the enormous energy necessary
to create mountains is not declining, even though our planet is several billion
years old.

An extraordinary story

Visitors whose curiosity is whetted by this unusual and varied panorama are not
satisfied with only a few questions and answers. They sense that here for the
asking is an extraordinary geologic (geo—earth; logic—science) story. With a
little direction, many subtle features become evident—features that otherwise
might escape notice. Here, for example, is a valley with an odd U-shape. There is
a sheer face crisscrossed with light- and dark-colored rocks. On the valley floor is
a tuft of pine trees that seem to be confined to one particular kind of rock. On the
rolling hills is a layer of peculiar white soil—the only soil in which coyote dens
are common. All these are geologically controlled phenomena. In short, with a bit
of initial guidance, the viewer gains an ability to observe and to understand so
much that the panorama takes on new depth, vividness, and excitement. It
changes from a flat, two-dimensional picture to a colorful multi-dimensional
exhibit of the earth’s history.

11

Figure 1. The Tetons from afar—an astronaut’s view of the range and adjacent mountains,
basins, and plateaus. Width of area shown in photo is about 100 miles. Stippled pattern marks
boundary of Grand Teton National Park.
High-resolution Map

12

Figure 2. Sketch of the Teton Range and Jackson Hole, southwest view. Drawing by J. R. Stacy.

BLOCK DIAGRAM VIEW SOUTHWEST SHOWING THE TETON RANGE AND
JACKSON HOLE

An astronaut’s view

The Tetons are a short, narrow, and high mountain range, distinctive in the midst
of the great chain of the Rocky Mountains, the backbone of western North
America. Figure 1 shows how the Tetons and their surroundings might appear if
you viewed them from a satellite at an altitude of perhaps a hundred miles. The
U. S. Geological Survey topographic map of Grand Teton National Park shows
the names of many features not indicated on figure 1 or on the geologic map
inside the back cover. The Teton Range is a rectangular mountain block about 40
miles long and 10-15 miles wide. It is flanked on the east and west by flat-floored
valleys. Jackson Hole is the eastern one and Teton Basin (called Pierre’s Hole by
the early trappers) is the western.

The Teton Range is not symmetrical. The highest peaks lie near the eastern edge
of the mountain block, rather than along its center, as is true in conventional
mountains, and the western slopes are broad and gentle in contrast to the 13
precipitous eastern slopes. The northern end of the range disappears under

enormous lava flows that form the Yellowstone Volcanic Plateau. Even from this
altitude the outlines of some of these flows can be seen.

On the south the Teton Range abuts almost at right angles against a northwest-
trending area of lower and less rugged mountains (the Snake River, Wyoming,
and Hoback Ranges). These mountains appear altogether different from the
Tetons. They consist of a series of long parallel ridges cut or separated by valleys
and canyons. This pattern is characteristic of mountains composed of crumpled,
steeply tilted rock layers—erosion wears away the softer layers, leaving the
harder ones standing as ridges.

On the east and northeast, Jackson Hole is bounded by the Gros Ventre and
Washakie Ranges, which are composed chiefly of folded hard and soft
sedimentary rocks. In contrast, between these mountains and the deepest 14
part of Jackson Hole to the west, thick layers of soft nearly flat-lying
sedimentary rocks have been sculptured by streams and ice into randomly
oriented knife-edge ridges and rolling hills separated by broad valleys. The hills
east of the park are called the Mount Leidy Highlands and those northeast are the
Pinyon Peak Highlands.

A pilot’s view

If you descend from 100 miles to about 5 miles above the Teton region, the
asymmetry of the range, the extraordinary variety of landscapes, and the vivid
colors of rocks become more pronounced.

Figure 2 shows a panorama of the Teton Range and Jackson Hole from a vantage
point over the Pinyon Peak Highlands. The rough steep slopes and jagged ridges
along the east front of the range contrast with smoother slopes and more rounded
ridges on the western side. Nestled at the foot of the mountains and extending out
onto the floor of Jackson Hole are tree-rimmed sparkling lakes of many sizes and
shapes. Still others lie in steep-sided rocky amphitheaters near the mountain
crests.

One of the most colorful flight routes into Jackson Hole is from the east, along
the north flank of the Gros Ventre Mountains. For 40 miles this mountain range is
bounded by broad parallel stripes of bright-red, pink, purple, gray, and brown
rocks. Some crop out as cliffs or ridges, and others are badlands (bare
unvegetated hills and valleys with steep slopes and abundant dry stream

channels). In places the soft beds have broken loose and flowed down slopes like
giant varicolored masses of taffy. These are mudflows and landslides. The
colorful rocks are bounded on the south by gray and yellow tilted layers forming
snowcapped peaks of the Gros Ventre Mountains.

These landscapes are the product of many natural forces acting on a variety of
rock types during long or short intervals of geologic time. Each group of rocks
records a chapter in the geologic story of the region. Other chapters can be read
from the tilting, folding, and breaking of the rocks. The latest episodes are written
on the face of the land itself.

15

A motorist’s view

Most park visitors first see the Teton peaks from the highway. Whether they drive
in from the south, east, or north, there is one point on the route at which a
spectacular panorama of the Tetons and Jackson Hole suddenly appears. Part of
the thrill of these three views is that they are so unexpected and so different. The
geologic history is responsible for these differences.

View north.—

Throughout the first 4 miles north of the town of Jackson, the view of the Tetons
from U. S. 26-89 is blocked by East Gros Ventre Butte. At the north end of the
butte, the highway climbs onto a flat upland at the south boundary of Grand
Teton National Park. Without any advance warning, the motorist sees the whole
east front of the Teton Range rising steeply from the amazingly flat floor of
Jackson Hole.

From the park boundary turnout no lakes or rivers are visible to the north but the
nearest line of trees in the direction of the highest Teton peaks marks the
approximate position of the Gros Ventre River. The elevation of this river is
surprising, for the route has just come up a 150-foot hill, out of the flat valley of a
much smaller stream, yet here at eye-level is a major river perched on an upland
plain. The reason for these strange relations is that the hill is a fault scarp (see fig.
16A for a diagram) and the valley in which the town of Jackson is located was
dropped 150 feet or more in the last 15,000 years.

On the skyline directly west of the turnout are horizontal and inclined layers of
rocks. These once extended over the tops of the highest peaks but were worn

away from some parts as the mountains rose. All along the range, trees grow only
up to treeline (also called timberline—a general elevation above which trees do
not grow) which here is about 10,500 feet above the sea. To the southeast and
east, beyond the sage-covered floor of Jackson Hole, are rolling partly forested
slopes marking the west end of the Gros Ventre Mountains. They do not look at
all like the Tetons because they were formed in a very different manner. The Gros
Ventres are folded mountains that have foothills; the Tetons are faulted mountains
that do not.

16
Figure 3. The Teton landscape as seen from Signal Mountain.

A. View west across Jackson Lake. Major peaks, canyons, and outcrops of sedimentary rocks are
indicated by “s.”
High-resolution View

17

B. View northeast; a study in contrast with the panorama above.
High-resolution View

Three steepsided hills called buttes rise out of the flat floor of Jackson Hole. 18
They are tilted and faulted masses of hard, layered rock that have been
shaped by southward-moving glaciers. Six miles north of the boundary turnout is
Blacktail Butte, on the flanks of which are west-dipping white beds. Southwest of
the turnout is East Gros Ventre Butte, composed largely of layered rocks that are
exposed along the road from Jackson almost to the turnout. These are capped by
very young lava that forms the brown cliff overlooking the highway at the north
end of the butte. To the southwest is West Gros Ventre Butte, composed of similar
rocks.

View west.—

The motorist traveling west along U. S. 26-287 is treated to two magnificent
views of the Teton Range. The first is 8 miles and the second 13 miles west of
Togwotee Pass. At these vantage points, between 20 and 30 miles from the
mountains, the great peaks seem half suspended between earth and sky—too
close, almost, to believe, but too distant to comprehend.

Only from closer range can the motorist begin to appreciate the size and
steepness of the mountains and to discern the details of their architecture. The
many roads on the floor of Jackson Hole furnish ever-changing vistas, and signs
provided by the National Park Service at numerous turnouts and scenic overlooks
help the visitor to identify quickly the major peaks and canyons and the principal
features of the valley floor. Of all these roadside vantage points, the top of Signal
Mountain, an isolated hill rising nearly 1,000 feet out of the east margin of
Jackson Lake, probably offers the best overall perspective (fig. 3). To the west,
across the shimmering blue waters of Jackson Lake, the whole long parade of
rugged peaks stretches from the north horizon to the south, many of the higher
ones wearing the tattered remnants of winter snow. From here, only 8 miles away,
the towering pinnacles, saw-toothed ridges, and deep U-shaped canyons are
clearly visible.

Unlike most other great mountain ranges, the Tetons rise steeply from the flat
valley floor in a straight unbroken line. The high central peaks tower more than a
mile above the valley, but northward and southward the peaks diminish in 19
height and lose their jagged character, gradually giving way to lower ridges
and rounded hills. Some of the details of the mountain rock can be seen—gnarled
gray rocks of the high peaks threaded by a fine white lacework of dikes, the dark
band that cleaves through Mount Moran from base to summit, and the light
brown and gray layers on the northern and southern parts of the range.

At first glance the floor of Jackson Hole south of Signal Mountain seems flat,
smooth, and featureless, except for the Snake River that cuts diagonally across it.
Nevertheless, even the flats show a variety of land forms. The broad sage-
covered areas, low isolated hills, and hummocky tree-studded ridges that form
the foreground are all parts of the Teton landscape, and give us clues to the
natural processes that shaped it. A critical look to the south discloses more
strange things. We take for granted the fact that the sides of normal valleys slope
inward toward a central major stream. South of Signal Mountain, however, the
visitor can see that the Snake River Valley does not fit this description. The broad
flat west of the river should slope east but it does not. Instead, it has been tilted
westward by downward movement along the Teton fault at the base of the
mountains.

View south.—

About a million motorists drive south from Yellowstone to Grand Teton National
Park each year. As they wind along the crooked highway on the west brink of
Lewis River Canyon (fig. 1), the view south is everywhere blocked by dense
forest. Then, abruptly the road leaves the canyon, straightens out, and one can
look south down a 3-mile sloping avenue cut through the trees. There, 20 to 30
miles away, framed by the roadway, are the snow-capped Tetons, with Jackson
Lake, luminous in reflected light, nestled against the east face. This is one of the
loveliest and most unusual views of the mountains that is available to the
motorist, partly because he is 800 feet above the level of Jackson Lake and partly
because this is the only place on a main highway where he can see clearly the
third dimension (width) of the Tetons. The high peaks are on the east edge; they
rise 7,000 feet above the lake but other peaks and precipitous ridges,
progressively diminishing in height, extend on to the west for a dozen miles 20
(fig. 14). Giant, relatively young lava flows, into which the Lewis River
Canyon was cut, poured southward all the way to the shore of Jackson Lake and
buried the north end of the Teton Range (figs. 13 and 53). South of Yellowstone
Park these flows were later tilted and broken by the dropping of Jackson Hole
and the rise of the mountains.

A mountaineer’s view

As in many pursuits in life, the greatest rewards of a visit to the Tetons come to
those who expend a real effort to earn them. Only by leaving the teeming valley

and going up into the mountains to hike the trails and climb the peaks can the
visitor come to know the Tetons in all their moods and changes and view close at
hand the details of this magnificent mountain edifice.

Even a short hike to Hidden Falls and Inspiration Point affords an opportunity for
a more intimate view of the mountains. Along the trail the hiker can examine
outcrops of sugary white granite, glittering mica-studded dikes, and dark
intricately layered rocks. Nearby are great piles of broken fragments that have
fallen from the cliffs above, and the visitor can begin to appreciate how
vulnerable are the towering crags to the relentless onslaught of frost and snow.
The roar of the foaming stream and the thunder of the falls are constant reminders
of the patient work of running water in wearing away the “everlasting hills.”
Running his hand across one of the smoothly polished rock faces below
Inspiration Point, the hiker gains an unforgettable concept of the power of glacial
ice and its importance in shaping this majestic landscape. Looking back across
Jenny Lake at the encircling ridge of glacial debris, he can easily comprehend the
size of the ancient glacier that once flowed down Cascade Canyon and emerged
onto the floor of Jackson Hole.

The more ambitious hiker or mountaineer can seek out the inner recesses of the
range and explore other facets of its geology. He can visit the jewel-like mountain
lakes—Solitude, Holly, and Amphitheater are just a few—cradled in high remote
basins left by the Ice Age glaciers. He can get a closeup view of the Teton 21
Glacier above Amphitheater Lake, or explore the Schoolroom Glacier, the
tiny ice body below Hurricane Pass. He may follow the trail into Garnet Canyon
to see the crystals from which the canyon takes its name and to examine the
soaring ribbonlike black dike near the end of the trail. In Alaska Basin he can
study the gently tilted layers of sandstone, limestone, and shale that once
blanketed the entire Teton Range and can search for the fossils that help
determine their age and decipher their history. From Hurricane Pass he can see
how these even layers of sedimentary rock have been broken and displaced and
how the older harder rocks that form the highest Teton peaks have been raised far
above them along the Buck Mountain fault.

Of all those who explore the high country, it is the mountaineer who has perhaps
the greatest opportunity to appreciate its geologic story. Indeed, the success of his
climb and his very life may depend on an intuitive grasp of the mountain geology
and the processes that shaped the peaks. He observes the most intimate details—
the inclination of the joints and fractures, which gullies are swept by falling
rocks, which projecting knobs are firm, and which cracks will safely take a piton.

To many climbers the ascent of a peak is a challenge to technical competence,
endurance, and courage, but to those endowed with curiosity and a sharp eye it
can be much more. As he stands shoulder to shoulder with the clouds on some
windswept peak, such as the Grand Teton, with the awesome panorama dropping
away on all sides, he can hardly avoid asking how this came to be. What does the
mountaineer see that inspires this curiosity? From the very first glance, it is
apparent that the scenes to the north, south, east, and west are startlingly
different.

Looking west from the rough, narrow, weather-ravaged granite summit of the
Grand Teton, one sees far below him the layered gray cliffs of marine
sedimentary rocks (solidified sediment originally deposited in a shallow arm of
the ocean) overlapping the granite and dipping gently west, finally disappearing
under the checkerboard farmland of Teton Basin. Still farther west are the rolling
timbered slopes of the Big Hole Range in Idaho. A glance at the foreground, 22
3,000 feet below, shows some unusual relations of the streams to the
mountains. The watershed divide of the Teton Range is not marked by the highest
peaks as one would expect. Streams in Cascade Canyon and in other canyons to
the north and south begin west of the peaks, bend around them, then flow
eastward in deep narrow gorges cut through the highest part of the range, and
emerge onto the flat floor of Jackson Hole.

In the view north along the crest of the Teton Range, the asymmetry of the
mountains is most apparent. The steep east face culminating in the highest peaks
contrasts with the lower more gentle west flank of the uplift. From the Grand
Teton it is not possible to see the actual place where the mountains disappear
under the lavas of Yellowstone Park, but the heavily timbered broad gentle
surface of the lava plain is visible beyond the peaks and extends across the entire
north panorama. Still farther north, 75 to 100 miles away, rise the snowcapped
peaks (from northwest to northeast) of the Madison, Gallatin, and Beartooth
Mountains.

The view east presents the greatest contrasts in the shortest distances—the flat
floor of Jackson Hole is 3 miles away and 7,000 feet below the top of the Grand
Teton. Along the junction of the mountains and valley floor are blue glacial lakes
strung out like irregular beads in a necklace. They are conspicuously rimmed by
black-appearing margins of pine trees that grow only on the surrounding glacial
moraines. Beyond these are the broad treeless boulder-strewn plains of Jackson
Hole. Fifty miles to the east and northeast, on the horizon beyond the rolling hills
of the Pinyon Peak Highlands, are the horizontally layered volcanic rocks of the

Absaroka Range. Southeast is the colorful red, purple, green, and gray Gros
Ventre River Valley, with the fresh giant scar of the Lower Gros Ventre Slide near
its mouth. Bounding the south side of this valley are the peaks of the Gros Ventre
Mountains, whose tilted slabby gray cliff-forming layers resemble (and are the
same as) those on the west flank of the Teton Range. Seventy miles away, in the
southeast distance, beyond the Gros Ventre Mountains are the shining 23
snowcapped peaks of the Wind River Range, the highest peak of which
(Gannett Peak) is about 20 feet higher than the Grand Teton.

Conspicuous on the eastern and southeastern skyline are high-level (11,000-
12,000 feet) flat-topped surfaces on both the Wind River and Absaroka Ranges.
These are remnants that mark the upper limit of sedimentary fill of the basins
adjacent to the mountains. A plain once connected these surfaces and extended
westward at least as far as the conspicuous flat on the mountain south of Lower
Gros Ventre Slide. It is difficult to imagine the amount of rock that has been
washed away from between these remnants in comparatively recent geologic
time, during and after the rise of the Teton Range.

From this vantage point the mountaineer also gets a concept of the magnitude of
the first and largest glaciers that scoured the landscape. Ice flowed
southwestward in an essentially unbroken stream from the Beartooth Mountains,
100 miles away, westward from the Absaroka Range, and northwestward from
the Wind River Range (fig. 57). Ice lapped up to treeline on the Teton Range and
extended across Jackson Hole nearly to the top of the Lower Gros Ventre Slide.
The Pinyon Peak and Mount Leidy Highlands were almost buried. All these
glaciers came together in Jackson Hole and flowed south within the ever-
narrowing Snake River Valley.

The view south presents a great variety of contrasts. Conspicuous, as in the view
north, is the asymmetry of the range. South of the high peaks of crystalline rocks,
gray layered cliffs of limestone extend in places all the way to the steep east face
of the Teton Range where they are abruptly cut off by the great Teton fault.

The flat treeless floor of Jackson Hole narrows southward. Rising out of the
middle are the previously described steepsided ice-scoured rocky buttes.
Beginning near the town of Jackson, part of which is visible, and extending as far
south as the eye can see are row upon row of sharp ridges and snowcapped peaks
that converge at various angles. These are the Hoback, Wyoming, Salt River, and
Snake River Ranges.

24

CARVING THE RUGGED PEAKS
The rugged grandeur of the Tetons is a product of four geologic factors: the tough
hard rocks in the core, the amount of vertical uplift, the recency of the mountain-
making movement, and the dynamic forces of destruction. Many other mountains
in Wyoming have just as hard rocks in their cores and an equally great amount of
vertical uplift, but they rose 50 to 60 million years ago and have been worn down
by erosion from that time on. The Tetons, on the other hand, are the youngest
range in Wyoming, less than 10 million years old, and have not had time to be so
deeply eroded.

Steep mountain slopes—the perpetual battleground

Any steep slope or cliff is especially vulnerable to nature’s methods of
destruction. In the Tetons we see the never-ending struggle between two
conflicting factors. The first is the extreme toughness of the rocks and their
consequent resistance to erosion. The second is the presence of efficient
transporting agencies that move out and away from the mountains all rock debris
that might otherwise bury the lower slopes.

The rocks making up most of the Teton Range are among the hardest, toughest,
and least porous known. Therefore, they resist mechanical disintegration by
temperature changes, ice, and water. They consist predominantly of minerals that
are subject to very little chemical decay in the cold climate of the Tetons.

Absence of weak layers prevents breaking of the tough rock masses under their
own weight. All these conditions, then, are favorable for preservation of steep
walls and high rock pinnacles. Nevertheless, they do break down. Great piles of
broken rock (talus) that festoon the slopes of all the higher peaks bear witness to
the unrelenting assault by the process of erosion upon the mountain citadels (figs.
4 and 31).

Rock disintegration and gravitational movement

A great variation in both daily and annual temperatures results in minute amounts
of contraction and expansion of rock particles. Repeated changes in volume 25
produce stress and strain. Although the rocks in the Tetons are very dense,
they eventually yield; a crack forms. Water which seeps in along this surface of
weakness freezes, either overnight or during long cold spells, and expands,
thereby prying a slab of rock away from the mountain wall. Repeated frost
wedging, as the process is called, results eventually in tipping the slab so that it
falls.

Figure 4. Talus at the foot of the jagged frost-riven peaks around Ice Floe Lake in the south fork
of Cascade Canyon. Photo by Philip Hyde.

What happens to the rock slab? It may fall and roll several hundred or thousand
feet, depending on the steepness of the mountain surface. Pieces are broken off as
it encounters obstacles. All the fragments find their way to a valley floor or slope,

where they momentarily come to rest. Thus, rock debris is moved 26
significant and easily observed distances by gravity.

None of this debris is stationary. If it is mixed with snow or saturated with water,
the whole mass may slowly flow in the same manner as a glacier. These are
called rock glaciers; some can be seen on the south side of Granite Canyon and
one, nearly a mile long, is in the valley north of Eagles Rest Peak.

The countless snow avalanches that thunder down the mountain flanks after
heavy winter snowfalls play their part, too, in gravitational transport. Loose rocks
and debris are incorporated with the moving snow and borne down the
mountainsides to the talus piles below. Trees, bushes, and soil are swept from the
sites of the slides, leaving conspicuous scars down the slopes and exposing new
rock surfaces to the attack of water and frost. Battered, broken, and uprooted
trees along many of the canyon trails bear silent witness to the awesome power of
snowslides.

These are some of the methods used by Nature in making debris and then, by
means of gravity, clearing it from the mountain slopes. There are other ways, too.
A weak layer of rock (usually one with a lot of clay in it), parallel to and
underlying a mountain slope, may occur between two hard layers. An extended
rainy spell may result in saturation of the weak zone so that it is well lubricated;
then an earthquake or perhaps merely the weight of the overlying rock sends the
now unstable mass cascading down the slope to the valley below. The famous
Lower Gros Ventre Slide (fig. 5) was formed in this way on June 23, 1925.

Running water cuts and carries

Running water is another effective agent that transports rock debris and has
helped dissect the Teton Range. The damage a broken water main can wreak on a
roadbed is well known, as is the havoc of destructive floods. The spring floods of
streams in the Tetons, swollen by melting snow and ice (annual precipitation,
mostly snow, in the high parts would average a layer of water 5 feet thick), move
some rock debris onto the adjoining floor of Jackson Hole.

27

Figure 5. The Lower Gros Ventre slide, air oblique view south. The top of the scar is 2,000 feet
above the river; the slide is more than a mile long and one-half mile wide. It dammed the Gros
Ventre River in the foreground, impounding a lake about 200 feet deep and 5 miles long. Gros
Ventre Mountains are in the distance. Photo by P. E. Millward.

Now and then the range is deluged by summer cloudbursts. Water funnels down
the maze of gullies on the mountainsides, quickly gathering volume and power,
and plunges on to the talus slopes below, as if from gigantic hoses. The sudden
onslaught of these torrents of water on the saturated unstable talus may trigger
enormous rock and mudflows that carry vast quantities of material down into the
canyons. During the summer of 1941 more than 100 of these flows occurred in
the park.

Wherever water moves, it carries rock fragments varying in size from boulders to
sand grains and on down to minute clay particles. Erosion (wearing away) by
streams is conspicuous wherever the water is muddy, as it always is each 28
spring in the Snake, Buffalo Fork, and Gros Ventre Rivers. Clear mountain
streams likewise can erode. Although the volume of material moved and the
amount of downcutting of the stream bottom may not seem great in a single

stream, the cumulative effect of many streams in an area, year after year and
century after century, is enormous. Streams not only transport rocks brought to
them by gravitational movement but also continually widen and deepen their
valleys, thereby increasing the volume of transported debris.

The effectiveness of streams as transporting agents in the Tetons is enhanced by
steep gradients (slopes); these increase water velocity which in turn expands the
capability of the streams to carry larger and larger rock fragments.

Glaciers scour and transport

Mountain landscapes shaped by frost action, gravitational transport, and stream
erosion alone generally have rounded summits, smooth slopes, and V-shaped
valleys. The jagged ridges, sharply pointed peaks, and deep U-shaped valleys of
the Tetons show that glaciers have played an important role in their sculpture.
The small present-day glaciers still cradled in shaded recesses among the higher
peaks (fig. 6) are but miniature replicas of great ice streams that occupied the
region during the Ice Age. Evidence both here and in other parts of the world
confirms that glaciers were once far more extensive than they are today.

Glaciers form wherever more snow accumulates during the winter than is melted
during the summer. Gradually the piles of snow solidify to form ice, which
begins to flow under its own weight. Rocks that have fallen from the surrounding
ridges or have been picked up from the underlying bedrock are incorporated in
the moving ice mass and carried along. The ability of ice to transport huge
volumes of rock is easily observed even in the small present-day glaciers in the
Tetons, all of which carry abundant rock fragments both on and within the ice.

29

Figure 6. The Teton Glacier on the north side of Grand Teton, air oblique view west. Photo by A.
S. Post, August 19, 1963.

Recent measurements show that the ice in the present Teton Glacier (fig. 6) 30
moves nearly 30 feet per year. The ancient glaciers, which were much wider

and deeper, may have moved as much as several hundred feet a year, like some of
the large glaciers in Alaska.

As the glacier moves down a valley, it scours the valley bottom and walls. The
efficiency of ice in this process is greatly increased by the presence of rock
fragments which act as abrasives. The valley bottom is plowed, quarried, and
swept clean of soil and loose rocks. Fragments of many sizes and shapes are
dragged along the bottom of the moving ice and the hard ones scratch long
parallel grooves in the underlying tough bedrock (fig. 7). Such grooves (glacial
striae) record the direction of ice movement.

The effectiveness of glaciers in cutting a U-shaped valley is particularly striking
in Glacier Gulch and Cascade Canyon (figs. 2 and 8).

The rock-walled amphitheater at the head of a glaciated valley is called a cirque
(a good example is at the upper edge of the Teton Glacier, fig. 6). The steep
cirque walls develop by frost action and by quarrying and abrasive action of the
glacier ice where it is near its maximum thickness. Commonly the glacier scoops
out a shallow basin in the floor of the cirque. Amphitheater Lake, Lake Solitude,
Holly Lake, and many of the other small lakes high in the Teton Range are
located in such basins.

The sharp peaks and the jagged knife-edge ridges so characteristic of the Tetons
are divides left between cirques and valleys carved by the ancient glaciers.

Effects on Jackson Hole

Rock debris is carried toward the end of the glacier or along the margins where it
is released as the ice melts. The semicircular ridge of rock fragments that marks
the downhill margin of the glacier is called a terminal moraine; that along the
sides is a lateral moraine (figs. 9 and 10). These are formed by the slow
accumulation of material in the same manner as that at the end of a conveyor belt.
They are not built by material pushed up ahead of the ice as if by a bulldozer.
Large boulders carried by ice are called erratics; many of these are scattered on
the floor of Jackson Hole and on the flanks of the surrounding mountains (fig.
11).

31

Figure 7. Rock surface polished and grooved by ice on the floor of Glacier Gulch.

Great volumes of water pour from melting ice near the lower end of a glacier.
These streams, heavily laden with rock flour produced by the grinding action of
the glacier and with debris liberated from the melting ice, cut channels through
the terminal moraine and spread a broad apron of gravel, sand, and silt down-
valley from the glacier terminus (end). Material deposited by streams issuing
from a glacier is called outwash; the sheet of outwash in front of the glacier is
called an outwash plain. If the terminus is retreating, masses of old stagnant ice
commonly are buried beneath the outwash; when these melt, the space they once
occupied becomes a deep circular or irregular depression called a kettle (fig. 12);
many of these now contain small lakes or swamps.

As a glacier retreats, it may build a series of terminal moraines, marking pauses
in the recession of the ice front. Streams issuing from the ice behind each new
terminal moraine are incised more and more deeply into the older moraines and
their outwash plains. Thus, new and younger layers of bouldery debris are spread
at successively lower and lower levels. These surfaces are called outwash
terraces.

32

Figure 8. East face of the Teton Range showing some of the glacial features, air oblique view.
Cascade Canyon, the U-shaped valley, was cut by ice. The glacier flowed toward the flats,
occupied the area of Jenny Lake (foreground), and left an encircling ring of morainal debris,
now covered with trees. The flat bare outwash plain in foreground was deposited by meltwater
from the glacier. The lake occupies a depression that was left when the ice melted away. National
Park Service photo by Bryan Harry.

33

Figure 9. Cutaway view of a typical valley glacier.

Figure 10. Recently-built terminal moraine of the Schoolroom Glacier, a small ice mass near the
head of the south fork of Cascade Canyon. The present glacier lies to the right just out of the
field of view. The moraine marks a former position of the ice terminus; the lake (frozen over in
this picture) occupies the depression left when the glacier wasted back from the moraine to its
present position. Crest of the moraine stands about 50 feet above the lake level. Many of the
lakes along the foot of the Teton Range occupy similar depressions behind older moraines. Photo
by Philip Hyde.

34

Figure 11. Large ice-transported boulder of coarse-grained pegmatite and granite resting on
Cretaceous shale near Mosquito Creek, on the southwest margin of Jackson Hole. Many
boulders at this locality are composed of pegmatite rock characteristic of the middle part of the
Teton Range. This occurrence demonstrates that boulders 40 feet in diameter were carried
southward 25 miles and left along the west edge of the ice stream, 1,500 feet above the base of
the glacier on the floor of Jackson Hole.

Just as the jagged ridges, U-shaped valleys, and ice-polished rocks of the Teton
Range attest the importance of glaciers in carving the mountain landscape, the
flat gravel outwash plains and hummocky moraines on the floor of Jackson Hole
demonstrate their efficiency in transporting debris from the mountains and
shaping the scenery of the valley.

Glaciers sculptured all sides of Jackson Hole and filled it with ice to an elevation
between 1,000 and 2,000 feet above the present valley floor. The visitor 35
who looks eastward from the south entrance to the park can see clearly
glacial scour lines that superficially resemble a series of terraces on the bare
lower slopes of the Gros Ventre Mountains. Southward-moving ice cut these
features in hard rocks. Elsewhere around the margins of Jackson Hole, especially
where the rocks are soft, evidence that the landscape was shaped by ice has been

partly or completely obliterated by later events. Rising 1,000 feet above the floor
of Jackson Hole are several steepsided buttes (figs. 13 and 55) described
previously, that represent “islands” of hard rock overridden and abraded by the
ice. After the ice melted, these buttes were surrounded and partly buried by
outwash debris.

Figure 12. “The Potholes,” knob and kettle topography caused by melting of stagnant ice partly
buried by outwash gravel. Air oblique view north from over Burned Ridge moraine (see fig. 61
for orientation). Photo by W. B. Hall and J. M. Hill.

The story of the glaciers and their place in the geologic history of the Teton
region is discussed in more detail later in this booklet.

36

Figure 13. Radar image of part of Tetons and Jackson Hole. Distance shown between left and
right margins is 35 miles. Lakes from left to right: Phelps, Taggart, Bradley, Jenny, Leigh,
Jackson. Blacktail Butte is at lower left. Channel of Snake River and outwash terraces are at
lower left. Burned Ridge and Jackson Lake moraines are in center. Lava flows at upper right
engulf north end of Tetons. Striated surfaces at lower right are glacial scour lines made by ice
moving south from Yellowstone National Park. Image courtesy of National Aeronautics and
Space Administration.

MOUNTAIN UPLIFT
Mountains appear ageless, but as with people, they pass through the stages of
birth, youth, maturity, and old age, and eventually disappear. The Tetons are
youthful and steep and are, therefore, extremely vulnerable to destructive
processes that are constantly sculpturing the rugged features and carrying away
the debris. The mountains are being destroyed. Although the processes of
destruction may seem slow to us, we know they have been operating for millions
of years—so why have the mountains not been leveled? How did they form in the
first place?

Kinds of mountains

There are many kinds of mountains. Some are piles of lava and debris erupted
from a volcano. Others are formed by the bowing up of the earth’s crust in the
shape of a giant dome or elongated arch. Still others are remnants of accumulated
sedimentary rocks that once filled a basin between preexisting mountains 37
and which are now partially worn away. An example of this type is the
Absaroka Range 40 miles northeast of the Tetons (figs. 1 and 52).

The Tetons are a still different kind—a fault block mountain range carved from a
segment of the earth’s crust that has been uplifted along a fault. The Teton fault is
approximately at the break in slope where the eastern foot of the range joins the
flats at the west edge of Jackson Hole (see map inside back cover), but in most
places is concealed beneath glacial deposits and debris shed from the adjacent
steep slopes. The shape of the range and its relation to Jackson Hole have already
been described. Clues as to the presence of the fault are: (1) the straight and deep
east face of the Teton Range, (2) absence of foothills, (3) asymmetry of the range
(fig. 14), and (4) small fault scarps (cliffs or steep slopes formed by faulting)
along the mountain front (fig. 15).

38

Figure 14. Air oblique view south showing the width and asymmetry of Teton Range. Grand
Teton is left of center and Mt. Moran is the broad humpy peak still farther left. Photo taken
October 1, 1965.

Recent geophysical surveys of Jackson Hole combined with data from deep wells
drilled in search of oil and gas east of the park also yield valuable clues. By
measuring variations in the earth’s magnetic field and in the pull of gravity and
by studying the speed of shock waves generated by small dynamite explosions,
Dr. John C. Behrendt of the U. S. Geological Survey has determined the depth
and tilt of rock layers buried beneath the veneer of glacial debris and stream-laid
sand and gravel on the valley floor. This information was used in constructing the
geologic cross section in the back of the booklet. The same rock layers that cap
the summit of Mount Moran (fig. 27) are buried at depths of nearly 24,000 feet
beneath the nearby floor of Jackson Hole but are cut off by the Teton fault at the
west edge of the valley. Thus the approximate amount of movement along the
fault here would be about 30,000 feet.

Anatomy of faults

The preceding discussion shows that the Tetons are an upfaulted mountain block.
Why is this significant? The extreme youth of the Teton fault, its large amount of
displacement, and the fact that the newly upfaulted angular mountain block was
subjected to intense glaciation are among the prime factors responsible for the

development of the magnificent alpine scenery of the Teton Range. An
understanding of the anatomy of faults is, therefore, pertinent. 39

Figure 15. Recent fault scarp (arrows indicate base) offsetting alluvial fan at foot of Rockchuck
Peak. View west from Cathedral Group scenic turnout. National Park Service photo by W. E.
Dilley and R. A. Mebane.

A fault is a plane or zone in the earth’s crust along which the rocks on one side
have moved in relation to the rocks on the other. There are various kinds of faults
just as there are various types of mountains. Three principal types of faults are
present in the Teton region: normal faults, reverse faults, and thrust faults. A
normal fault (fig. 16A) is a steeply dipping (steeply inclined) fault along which
rocks above the fault have moved down relative to those beneath it. A reverse
fault (fig. 16B) is a steeply inclined fault along which the rocks above the fault
have moved up relative to those below it. A thrust fault (fig. 16C) is a gently
inclined fault along which the principal movement has been more nearly
horizontal than vertical.

Normal faults may be the result of tension or pulling apart of the earth’s crust or
they may be caused by adjustment of the rigid crust to the flow of semi-fluid
material below. The crust sags or collapses in areas from which the subcrustal
material has flowed and is bowed up and stretched in areas where excess
subcrustal material has accumulated. In both areas the adjustments may result in
normal faults.

Reverse faults are generally caused by compression of a rigid block of the crust,
but some may also be due to lateral flow of subcrustal material.

Thrust faults are commonly associated with tightly bent or folded rocks. 40
Many of them are apparently caused by severe compression of part of the
crust, but some are thought to have formed at the base of slides of large rock
masses that moved from high areas into adjacent low areas under the influence of
gravity.

The Teton fault (see cross section inside back cover) is a normal fault; the Buck
Mountain fault, which lies west of the main peaks of the Teton Range, is a
reverse fault. No thrust faults have been recognized in the Teton Range, but the
mountains south and southwest of the Tetons (fig. 1) display several enormous
thrust faults along which masses of rocks many miles in extent have moved tens
of miles eastward and northeastward.

Time and rate of uplift

When did the Tetons rise?

A study of the youngest sedimentary rocks on the floor of Jackson Hole shows
that the Teton Range began to rise rapidly and take its present shape less than 9
million years ago. The towering peaks themselves are direct evidence that the rate
of uplift far exceeded the rate at which the rising block was worn away by
erosion. The mountains are still rising, and comparatively rapidly, as is indicated
by small faults cutting the youngest deposits (fig. 15).

How rapidly? Can the rate be measured?

We know that in less than 9 million years (and probably in less than 7 million
years) there has been 25,000 to 30,000 feet of displacement on the Teton fault.
This is an average of about 1 foot in 300-400 years. The movement probably was

not continuous but came as a series of jerks accompanied by violent earthquakes.
One fault on the floor of Jackson Hole near the southern boundary of the park
moved 150 feet in the last 15,000 years, an average of 1 foot per 100 years.

In view of this evidence of recent crustal unrest, it is not surprising that small
earthquakes are frequent in the Teton region. More violent ones can probably be
expected from time to time.

41
Figure 16. Types of faults.

A.—Normal fault (tensional)

B.—Reverse fault (compressional)

C.—Thrust fault (compressional)

Why are mountains here?

Why did the Tetons form where they are?

At the beginning of this booklet we discussed briefly the two most common
theories of origin of mountains: continental drift and convection currents. The
question of why mountains are where they are and more specifically why the
Tetons are here remains a continuing scientific challenge regardless of the wealth
of data already accumulated in our storehouse of knowledge.

The mobility of the earth’s crust is an established fact. Despite its apparent
rigidity, laboratory experiments demonstrate that rocks flow when subjected to
extremely high pressures and temperatures. If the stress exceeds the strength at a
given pressure and temperature, the rock breaks. Flowing and fracturing are two
of the ways by which rocks adjust to the changing environments at various levels
in the earth’s crust. These acquired characteristics, some of which can be
duplicated in the laboratory, are guides by which we interpret the geologic history
of rocks that once were deep within the earth.

The site of the Teton block no doubt reflects hidden inequalities at depth. 42
We cannot see these, nor in this area can we drill below the outer layer of
the earth; nevertheless, measurements of gravity and of the earth’s magnetic field
clearly show that they exist.

We know that the Tetons rose at the time Jackson Hole collapsed but the volume
of the uplifted block is considerably less than that of the downdropped block.
This, then, was not just a simple case in which all the subcrustal material
displaced by the sinking block was squeezed under the rising block (the way a
hydraulic jack works). What happened to the rest of the material that once was
under Jackson Hole? It could not be compressed so it had to go somewhere.

As you look northward from the top of the Grand Teton or Mount Moran, or from
the main highway at the north edge of Grand Teton National Park, you see the
great smooth sweep of the volcanic plateau in Yellowstone National Park. Farther
off to the northeast are the strikingly layered volcanic rocks of the Absaroka
Range (fig. 52). For these two areas, an estimate of the volume of volcanic rock
that reached the surface and flowed out, or was blown out and spread far and

wide by wind and water, is considerably in excess of 10,000 cubic miles. On the
other hand, this volume is many times more than that displaced by the sagging
and downfaulting of Jackson Hole.

Where did the rest of the volcanic material come from? Is it pertinent to our
story? Teton Basin, on the west side of the Teton Range, and the broad Snake
River downwarp farther to the northwest (fig. 1) are sufficiently large to have
furnished the remainder of the volcanic debris. As it was blown out of vents in
the Yellowstone-Absaroka area, its place could have been taken deep
underground by material that moved laterally from below all three downdropped
areas. The movement may have been caused by slow convection currents within
the earth, or perhaps by some other, as yet unknown, force. The sagging of the
earth’s crust on both sides of the Teton Range as well as the long-continued
volcanism are certainly directly related to the geologic history of the park.

In summary, we theorize as to how the Tetons rose and Jackson Hole sank 43
but are not sure why the range is located at this particular place, why it
trends north, why it rose so high, or why this one, of all the mountain ranges
surrounding the Yellowstone-Absaroka volcanic area, had such a unique history
of uplift. These are problems to challenge the minds of generations of earth
scientists yet to come.

The restless land

Among the greatest of the park’s many attractions is the solitude one can savor in
the midst of magnificent scenery. Only a short walk separates us from the
highway, torrents of cars, noise, and tension. Away from these, everything seems
restful.

Quiescent it may seem, yet the landscape is not static but dynamic. This is one of
the many exciting ideas that geology has contributed to society. The concept of
the “everlasting hills” is a myth. All the features around us are actually rather
short-lived in terms of geologic time. The discerning eye detects again and again
the restlessness of the land. We have discussed many bits of evidence that show
how the landscape and the earth’s crust beneath it are constantly being carved,
pushed up, dropped down, folded, tilted, and faulted.

The Teton landscape is a battleground, the scene of a continuing unresolved
struggle between the forces that deform the earth’s crust and raise the mountains

and the slow processes of erosion that strive to level the uplands, fill the hollows,
and reduce the landscape to an ultimate featureless plain. The remainder of this
booklet is devoted to tracing the seesaw conflict between these inexorable
antagonists through more than 2.5 billion years as they shaped the present
landscape—and the battle still goes on.

Evidence of the struggle is all around us. Even though to some observers it may
detract from the restfulness of the scene, perhaps it conveys to all of us a new
appreciation of the tremendous dynamic forces responsible for the magnificence
of the Teton Range.

The battle is indicated by the small faults that displace both the land surface and
young deposits at the east base of Mount Teewinot, Rockchuck Peak (fig. 44
15), and other places along the foot of the Tetons.

Jackson Hole continues to drop and tilt. The gravel-covered surfaces that
originally sloped southward are now tilted westward toward the mountains. The
Snake River, although the major stream, is not in the lowest part of Jackson Hole;
Fish Creek, a lesser tributary near the town of Wilson, is 15 feet lower. For 10
miles this creek flows southward parallel to the Snake River but with a gentler
gradient, thus permitting the two streams to join near the south end of Jackson
Hole. As tilting continues, the Snake River west of Jackson tries to move
westward but is prevented from doing so by long flood-control levees built south
of the park.

Recent faults also break the valley floor between the Gros Ventre River and the
town of Jackson.

The ever-changing piles of rock debris that mantle the slopes adjacent to the
higher peaks, the creeping advance of rock glaciers, the devastating snow
avalanches, and the thundering rockfalls are specific reminders that the land
surface is restless. Jackson Hole contains more landslides and rock mudflows
than almost any other part of the Rocky Mountain region. They constantly plague
road builders (fig. 17) and add to the cost of other types of construction.

All of these examples of the relentless battle between constructive and
destructive processes modifying the Teton landscape are but minor skirmishes.
The bending and breaking of rocks at the surface are small reflections of
enormous stresses and strains deep within the earth where the major conflict is
being waged. It is revealed every now and then by a convulsion such as the 1959

earthquake in and west of Yellowstone Park. Events of this type release much
more energy than all the nuclear devices thus far exploded by man.

45

Figure 17. Slide blocking main highway in northern part of Grand Teton National Park.
National Park Service photo by Eliot Davis, May 1952.

ENORMOUS TIME AND DYNAMIC EARTH

Framework of time

One of geology’s greatest philosophical contributions has been the demonstration
of the enormity of geologic time. Astronomers deal with distances so great that
they are almost beyond understanding; nuclear physicists study objects so small
that we can hardly imagine them. Similarly, the geologist is concerned with spans
of time so immense that they are scarcely comprehensible. Geology is a science
of time as well as rocks, and in our geologic story of the Teton region we must
refer frequently to the geologic time scale, the yardstick by which we measure the
vast reaches of time in earth history.

Rocks and relative age

Very early in the science of geology it was recognized that in many places one
can tell the comparative ages of rocks by their relations to one another. For
example, most sedimentary rocks are consolidated accumulations of large or
small rock fragments and were deposited as nearly horizontal layers of 46
gravel, sand, or mud. In an undisturbed sequence of sedimentary rocks, the
layer on the bottom was deposited first and the layer on top was deposited last.
All of these must, of course, be younger than any previously formed rock
fragments incorporated in them.

Igneous rocks are those formed by solidification of molten material, either as lava
flows on the earth’s surface (extrusive igneous rocks) or at depth within the earth
(intrusive igneous rocks). The relative ages of extrusive igneous rocks can often
be determined in much the same way as those of sedimentary strata. A lava flow
is younger than the rocks on which it rests, but older than those that rest on top of
it.

An intrusive igneous rock must be younger than the rocks that enclosed it at the
time it solidified. It may contain pieces of the enclosing rocks that broke off the
walls and fell into the liquid. Pebbles of the igneous rock that are incorporated in
nearby sedimentary layers indicate that the sediments must be somewhat
younger.

All of these criteria tell us only that one rock is older or younger than another.
They tell us little about the absolute age of the rocks or about how much older
one is than the other.

Fossils and geologic time

Fossils provide important clues to the ages of the rocks in which they are found.
The slow evolution of living things through geologic time can be traced by a
systematic study of fossils. The fossils are then used to determine the relative
ages of the rocks that contain them and to establish a geologic time scale that can
be applied to fossil-bearing rocks throughout the world. Figure 18 shows the
major subdivisions of the last 600 million years of geologic time and some forms
of life that dominated the scene during each of these intervals. Strata containing
closely related fossils are grouped into systems; the time interval during which
the strata comprising a particular system were deposited is termed a period. The
periods are subdivisions of larger time units called eras and some are split into
smaller time units called epochs. Strata deposited during an epoch comprise 47
a series. Series are in turn subdivided into rock units called groups and
formations. Expressed in tabular form these divisions are:

Subdivisions of geologic time Time-rock units Rock units
Era
Period System
Epoch Series
Group
Formation

The time scale based on the study of fossil-bearing sedimentary rocks is called
the stratigraphic time scale; it is given in table 1. The subdivisions are arranged in
the same order in which they were deposited, with the oldest at the bottom and
the youngest at the top. All rocks older than Cambrian (the first period in the

Paleozoic Era) are classed as Precambrian. These rocks are so old that fossils are
rare and therefore cannot be conveniently used as a basis for subdivision.

The stratigraphic time scale is extremely useful, but it has serious drawbacks. It
can be applied only to fossil-bearing strata or to rocks whose ages are determined
by their relation to those containing fossils. It cannot be used directly for rocks
that lack fossils, such as igneous rocks, or metamorphic rocks in which fossils
have been destroyed by heat or pressure. It is used to establish the relative ages of
sedimentary strata throughout the world, but it gives no information as to how
long ago a particular layer was deposited or how many years a given period or
era lasted.

Radioactive clocks

The measurement of geologic time in terms of years was not possible until the
discovery of natural radioactivity. It was found that certain atoms of a few
elements spontaneously throw off particles from their nuclei and break down to
form atoms of other elements. These decay processes take place at constant rates,
unaffected by heat, pressure, or chemical conditions. If we know the rate at which
a particular radioactive element decays, the length of time that has passed since a
mineral crystal containing the elements formed can be calculated by comparing
the amount of the radioactive element remaining in the crystal with the amount of
disintegration products present.

48

Figure 18. Major subdivisions of the last 600 million years of geologic time and some of the
dominant forms of life.

MILLIONS OF
YEARS AGO
0 Man
0-60 CENOZOIC QUATERNARY and Mammals
TERTIARY
60-130 MESOZOIC CRETACEOUS
130-180 JURASSIC Dinosaurs
180-220 TRIASSIC
220-260 PALEOZOIC PERMIAN Reptiles
260-350 PENNSYLVANIAN, Amphibians
MISSISSIPPIAN
350-400 DEVONIAN Fishes
400-440 SILURIAN Sea scorpions
440-500 ORDOVICIAN Nautiloids
500-530 CAMBRIAN Trilobites

530- PRECAMBRIAN Soft-bodied
creatures

Three principal radioactive clocks now in use are based on the decay of uranium
to lead, rubidium to strontium, and potassium to argon. They are effective in
dating minerals millions or billions of years old. Another clock, based on the
decay of one type of carbon (Carbon-14) to nitrogen, dates organic material, but
only if it is less than about 40,000 years old.

The uranium, rubidium, and potassium clocks are especially useful in dating
igneous rocks. By determining the absolute ages of igneous rocks whose
stratigraphic relations to fossil-bearing strata are known, it is possible to estimate
the number of years represented by the various subdivisions of the stratigraphic
time scale.

The yardstick of geologic time

Recent estimates suggest that the earth was formed at least 4.5 billion years ago.
To visualize the length of geologic time and the relations between the
stratigraphic and absolute time scales, let us imagine a yardstick as representing
the length of time from the origin of the earth to the present (fig. 19). On one side
of the yardstick we plot time in years; on the other, we plot the divisions of 49
the stratigraphic time scale according to the most reliable absolute age
determinations.

Table 1. The stratigraphic time scale.

Era System or period Series or epoch
Cenozoic Quaternary Recent
Pleistocene
Tertiary Pliocene
Miocene
Oligocene
Eocene
Paleocene
Mesozoic Cretaceous
Jurassic

Triassic
Paleozoic Permian
Pennsylvanian
Mississippian
Devonian
[1]
Silurian
Ordovician
Cambrian
— Precambrian

[1]
The Silurian is the only major subdivision of the stratigraphic time scale not
represented in Grand Teton National Park.

We are immediately struck by the fact that all of the subdivisions of the
stratigraphic time scale since the beginning of the Paleozoic are compressed into
the last 5 inches of our yardstick! All of the other 31 inches represent
Precambrian time. We also see that subdivisions of the stratigraphic time scale do
not represent equal numbers of years. We use smaller and smaller subdivisions as
we approach the present. (Notice the subdivisions of the Tertiary and Quaternary
in table 1 that are too small to show even in the enlarged part of figure 19). This
is because the record of earth history is more vague and incomplete the farther
back in time we go. In effect, we are very nearsighted in our view of time. This
“geological myopia” becomes increasingly evident throughout the remainder of
this booklet.

50

Figure 19. The geologic time scale—our yardstick in time.

ABSOLUTE TIME (Years STRATIGRAPHIC TIME
ago) INCHES SCALE
First man → 0 CENOZOIC
1 MESOZOIC
First dinosaurs → 2 PALEOZOIC
3
500 million 4
First abundant fossils → 5 PRECAMBRIAN
6

7
1 billion 8
9
10
11
12
13
14
Oldest known fossils → 15
2 billion 16
17
18
19
20
21
22
23
3 billion 24
25
26
27
Oldest dated rocks → 28
29
30
31
4 billion 32
33
34
35
Minimum age of the earth → 36
ENLARGEMENT OF THE LAST SIX
INCHES
ABSOLUTE TIME (Years
Ago) INCHES STRATIGRAPHIC TIME SCALE

0 0 CENOZOIC QUATERNARY
TERTIARY
MESOZOIC CRETACEOUS
1 JURASSIC
TRIASSIC
2 PALEOZOIC PERMIAN
PENNSYLVANIAN
MISSISSIPPIAN
3 DEVONIAN
SILURIAN
ORDOVICIAN
500 million 4 CAMBRIAN
5 PRECAMBRIAN
6
51

PRECAMBRIAN ROCKS—THE CORE OF THE
TETONS
The visitor who looks at the high, rugged peaks of the Teton Range is seeing
rocks that record about seven-eighths of all geologic time. These Precambrian
rocks are part of the very foundation of the continent and are therefore commonly
referred to by geologists as basement rocks. In attempting to decipher their origin
and history we peer backward through the dim mists of time, piecing together
scattered clues to events that occurred billions of years ago, perhaps during the
very birth of the North American Continent. To cite an oft-quoted example, it is
as though we were attempting to read the history of an ancient and long-forgotten
civilization from the scattered unnumbered pages of a torn manuscript, written in
a language that we only partially understand.

Ancient gneisses and schists

The oldest Precambrian rocks in the Teton Range are layered gneisses and schists
exposed over wide areas in the northern and southern parts of the range and as
scattered isolated masses in the younger granite that forms the high peaks in the
central parts. The layered gneisses may be seen easily along the trails in the lower
parts of Indian Paintbrush and Death Canyons, and near Static Peak.

The layered gneisses are composed principally of quartz, feldspar, biotite (black
mica), and hornblende (a very dark-green or black mineral commonly forming
rodlike crystals). Distinct layers, a few inches to several feet thick, contain
different proportions of these minerals and account for the banded appearance.
Layers composed almost entirely of quartz and feldspar are light-gray or white,
whereas darker gray layers contain higher proportions of biotite and hornblende.

Some layers are dark-green to black amphibolite, composed principally of
hornblende but with a little feldspar and quartz. In many places the gneisses
include layers of schist, a flaky rock, much of which is mica. At several places on
the east slopes of Mount Moran thin layers of impure gray marble are found

interleaved with the gneisses. West of Static Peak along the Alaska Basin 52
Trail a heavy dark rock with large amounts of magnetite (strongly magnetic
black iron oxide) occurs as layers in the gneiss.

In some places the gneiss contains dark-reddish crystals of garnet as much as an
inch in diameter. Commonly the garnet crystals are surrounded by white “halos”
which lack biotite or hornblende, probably because the constituents necessary to
form these minerals were absorbed by the garnet crystals. In Death Canyon and
on the slopes of Static Peak some layers of gray gneiss contain egg-shaped
masses of magnetite as much as one-half inch in diameter (fig. 20). These masses
are likewise surrounded by elliptical white halos and have the startling
appearance of small eyes peering from the rock. Appropriately, this rock has been
called the “bright-eyed” gneiss by Prof. Charles C. Bradley in his published study
(Wyoming Geological Association, 1956) of this area.

What were the ancient rocks from which the gneisses of the Teton Range were
formed? Most of the evidence has been obliterated but a few remaining clues
enable us to draw some general conclusions. The banded appearance of many of
the gneisses suggests that they were formed from sedimentary and volcanic rocks
that accumulated on the sea floor near a chain of volcanic islands—perhaps
somewhat similar to the modern Aleutians or the islands of Indonesia. When
these deposits were buried deep in the earth’s crust the chemical composition of
some layers may have undergone radical changes. Other layers, however, still
have compositions resembling those of younger rocks elsewhere whose origins
are better known. For example, the layers of impure marble were probably once
beds of sandy limestone, and the lighter colored gneiss may have been muddy
sandstone, possibly containing volcanic ash. Some dark amphibolite layers could
represent altered lava flows or beds of volcanic ash; others may have resulted
from the addition of silica to muddy magnesium-rich limestone during
metamorphism. The magnetite-rich gneiss probably was originally a sedimentary
iron ore.

53

Figure 20. “Bright-eyed” gneiss from Death Canyon. The dark magnetite spots are about ¼ inch
in diameter. The surrounding gneiss is composed of quartz, feldspar, and biotite, but biotite is
missing in the white halos around the magnetite.

Minerals that were most easily altered at depth reacted with one another to form
new minerals more “at home” under the high temperature and pressure in this
environment just as the ingredients in a cake react when heated in an oven. Rocks
formed by such processes are called metamorphic rocks; careful studies of the
minerals that they contain suggest that the layered gneisses developed at
temperatures as high as 1000°F at depths of 5 to 10 miles. Under these conditions
the rocks must have behaved somewhat like soft taffy as is shown by layers that
have been folded nearly double without being broken (fig. 21). Folds such as
these range from fractions of an inch to thousands of feet across and are found in
gneisses throughout the Teton Range. In a few places folds are superimposed in
such a way as to indicate that the rocks were involved in several episodes of
deformation in response to different sets of stress during metamorphism.

When did these gneisses form? Age determinations of minerals containing
radioactive elements show that granite which was intruded into them after they
were metamorphosed and folded is more than 2.5 billion years old. They must,
therefore, be older than that. Thus, they probably are at least a billion years older

than rocks containing the first faint traces of life on earth and 2 billion years older
than the oldest rocks containing abundant fossils. How much older is not known,
but the gneisses are certainly among the oldest rocks in North America and 54
record some of the earliest events in the building of this continent.

Figure 21. Folds in layered gneisses.

A. North face of the ridge west of Eagles Rest Peak. The face is about 700 feet high. Notice the
extreme contortion of the gneiss layers.

B. Closeup view of some of the folds near the bottom of the face in figure A. The light-colored
layers are composed principally of quartz and feldspar. The darker layers are rich in hornblende.

Irregular bodies of granite gneiss are interleaved with the layered gneisses in the
northern part of the Teton Range. The granite gneiss is relatively coarse grained,
streaky gray or pink, and composed principally of quartz, feldspar, biotite, and
hornblende. It differs from enclosing layered gneisses in its coarser texture, lack
of layering, and more uniform appearance. The dark minerals (biotite and 55
hornblende) are concentrated in thin discontinuous wisps that give the rock
its streaky appearance.

The largest body of granite gneiss is exposed in a belt 1 to 2 miles wide and 10
miles long extending northeastward from near the head of Moran Canyon, across
the upper part of Moose Basin, and into the lower reaches of Webb Canyon. This
gneiss may have been formed from granite that invaded the ancient sedimentary
and volcanic rocks before they were metamorphosed, or it may have been formed
during metamorphism from some of the sediments and volcanics themselves.

At several places in Snowshoe, Waterfalls, and Colter Canyons the layered
gneisses contain discontinuous masses a few tens or hundreds of feet in diameter
of heavy dark-green or black serpentine. This rock is frequently called
“soapstone” because the surface feels smooth and soapy to the touch. Indians
carved bowls (fig. 22) from similar material obtained from the west side of the
Tetons and from the Gros Ventre Mountains to the southeast. Pebbles of
serpentine along streams draining the west side of the Tetons have been cut and
polished for jewelry and sold as “Teton jade”; it is much softer and less lustrous
than real jade. The serpentine was formed by metamorphism of dark-colored
igneous rocks lacking quartz and feldspar.

Granite and pegmatite

Contrary to popular belief, granite (crystalline igneous rock composed
principally of quartz and feldspar) forms only a part of the Teton Range. The
Grand Teton (fig. 6) and most surrounding subsidiary peaks are sculptured from
an irregular mass of granite exposed continuously along the backbone of the
range from Buck Mountain northward toward upper Leigh Canyon. The rock is
commonly fine grained, white or light-gray, and is largely composed of crystals
of gray quartz and white feldspar about the size and texture of the grains in very
coarse lump sugar. Flakes of black or dark-brown mica (biotite) and silvery white
mica (muscovite) about the size of grains of pepper are scattered through the
rock.

From the floor of Jackson Hole the granite cliffs and buttresses of the high 56
peaks appear nearly white in contrast to the more somber grays and browns
of surrounding gneisses and schists. These dark rocks are laced by a network of
irregular light-colored granite dikes ranging in thickness from fractions of an inch
to tens of feet (fig. 23).

Figure 22. Indian bowls carved from soapstone, probably from the Teton Range. Mouth of the
unbroken bowl is about 4 inches in diameter.

The largest masses of granite contain abundant unoriented angular blocks and
slabs of the older gneisses. These inclusions range from a few inches in diameter
(fig. 24) to slabs hundreds of feet thick and thousands of feet long.

Dikes or irregular intrusions of pegmatite are found in almost every exposure of
granite. Pegmatite contains the same minerals as granite but the individual
mineral crystals are several inches or even as much as a foot in diameter.

Some pegmatites contain silvery plates or tabular crystals of muscovite mica as
much as 6 inches across that can be split into transparent sheets with a pocket
knife. Others have dark-brown biotite mica in crystals about the size and shape of
the blade of a table knife.

A few pegmatites contain scattered red-brown crystals of garnet ranging in size
from that of a BB shot to a small marble; a few in Garnet Canyon and Glacier
Gulch are larger than baseballs (fig. 25). The garnets are fractured and many are
partly altered to chlorite (a dull-green micaceous mineral) so they are of no value
as gems.

57
Figure 23. Dikes of granite and pegmatite.

A. Network of light-colored granite dikes on the northeast face of the West Horn on Mt. Moran.
The dikes cut through gneiss in which the layers slant steeply downward to the left. The face is
about 700 feet high. Snowfield in the foreground is at the edge of the Falling Ice Glacier.

B. Irregular dike of granite and pegmatite cutting through dark layered gneisses near Wilderness
Falls in Waterfalls Canyon. The cliff face is about 80 feet high. Contacts of the dike are sharp
and angular and cut across the layers in the enclosing gneiss.

Pegmatite dikes (tabular bodies of rock that, while still molten, were forced 58
along fractures in older rocks) commonly cut across granite dikes, but in
many places the reverse is true. Some dikes are composed of layers of pegmatite
alternating with layers of granite (fig. 26), showing that the pegmatite and granite
are nearly contemporaneous. Prof. Bruno Giletti and his coworkers at Brown
University, using the rubidium-strontium radioactive clock, determined that the
granite and pegmatite in the Teton Range are about 2.5 billion years old.

Figure 24. Angular blocks of old streaky granite gneiss in fine-grained granite northwest of
Lake Solitude. The difference in orientation of the streaks in the gneiss blocks indicates that the
blocks have been rotated with respect to one another and that the fine-grained granite must
therefore have been liquid at the time of intrusion. A small light-colored dike in the upper left-
hand block of gneiss ends at the edge of the block; it intruded the gneiss before the block was
broken off and incorporated in the granite. A small dike of pegmatite cuts diagonally through the
granite just to the left of the hammer and extends into the blocks of gneiss at both ends. This
dike was intruded after the granite had solidified. Thus, in this one small exposure we can
recognize four ages of rocks: the streaky granite gneiss, the light-colored dike, the fine-grained
granite, and the small pegmatite dike.

Black dikes

Even the most casual visitor to the Teton Range notices the remarkable black
band that extends down the east face of Mount Moran (figs. 27 and 28) 59
from the summit and disappears into the trees north of Leigh Lake. This is
the outcropping edge of a steeply inclined dike composed of diabase, a nearly
black igneous rock very similar to basalt. Thinner diabase dikes are visible on the
east face of Middle Teton, on the south side of the Grand Teton, and in several
other places in the range (see geologic map inside back cover).

Figure 25. Garnet crystal in pegmatite. The crystal is about 6 inches in diameter. Other minerals
are feldspar (white) and clusters of white mica flakes. The mica crystals appear dark in the
photograph because they are wet.

The diabase is a heavy dark-greenish-gray to black rock that turns rust brown on
faces that have been exposed to the weather. It is studded with small lath-shaped
crystals of feldspar that are greenish gray in the fresh rock and milk white on
weathered surfaces.

The black dikes formed from molten rock that welled up into nearly vertical
fissures in the older Precambrian rocks. Toward the edges of the dikes the 60
feldspar laths in the diabase become smaller and smaller (fig. 29),
indicating that the wall rocks were relatively cool when the magma or melted
rock was intruded. Rapid chilling at the edges prevented growth of large crystals.
In many places hot solutions from the dike permeated the wall rocks, staining
them rosy red.

Figure 26. A small dike of pegmatite and granite cutting through folded layered gneiss in Death
Canyon. Coarse-grained pegmatite forms most of the dike, but fine-grained granite is found near
the center. Small offshoots of the dike penetrate into the wall rocks. The dike cuts straight across
folds in the enclosing gneisses and must therefore have been intruded after development of the
folds. The white ruler is about 6 inches long.

The black dike on Mount Moran is about 150 feet thick near the summit of the
peak. This dike has been traced westward for more than 7 miles. Where it passes
out of the park south of Green Lakes Mountain it is 100 feet thick. The amount of
molten material needed to form the exposed segment of this single dike could fill
Jenny Lake three times over. The other dikes are thinner and not as long: the dike
on Middle Teton is 20 to 40 feet thick, and the dike on Grand Teton is 40 to 60
feet thick.

61

Figure 27. Air oblique view of the east face of Mt. Moran, showing the great black dike. Main
mass of the mountain is layered gneiss and streaky granite gneiss. White lines are dikes of
granite and pegmatite; light-gray mound on the summit is about 50 feet of Cambrian
sedimentary rock (Flathead Sandstone). Notice that the black dike cuts across the dikes of
granite and pegmatite but that its upper edge is covered by the much younger layer of sandstone.
Falling Ice Glacier is in the left center; Skillet Glacier is in the lower right center. Photo by A. S.
Post. University of Washington, August 19, 1963.

62

Figure 28. The great black dike on the east face of Mt. Moran. The dike is about 150 feet thick
and its vertical extent in the picture is about 3,000 feet. The fractures in the dike perpendicular
to its walls are cracks formed as the liquified rock cooled and crystallized. Falling Ice Glacier is
in the center. National Park Service photo by H. D. Pownall.

63

Figure 29. Closeup view of the edge of the Middle Teton black dike exposed on the north wall of
Garnet Canyon near the west end of the trail. Dike rock (diabase) is on the right; wall rock
(gneiss) is on the left. Match shows scale.

The black dikes must be the youngest of the Precambrian units because they cut
across all other Precambrian rocks. The dikes must have been intruded before the
beginning of Cambrian deposition inasmuch as they do not cut the oldest
Cambrian beds. Gneiss adjacent to the dike on Mount Moran contains biotite that
was heated and altered about 1.3 billion years ago according to Professor Giletti.
The alteration is believed to have occurred when the dike was emplaced;
therefore this and similar dikes elsewhere in the range are probably about 1.3
billion years old.

Quartzite

At about the same time as the dikes were being intruded in the Tetons, many
thousands of feet of sedimentary rocks, chiefly sandstone, were deposited in
western Montana, 200 miles northwest of Grand Teton National Park. The
sandstone was later recrystallized and recemented and became a very dense hard
rock called quartzite. Similar quartzite, possibly part of the same deposit, was

laid down west of the north end of the Teton Range, within the area now called
the Snake River downwarp (fig. 1).

The visitor who hikes or camps anywhere on the floor of Jackson Hole becomes
painfully aware of the thousands upon thousands of remarkably rounded hard
quartzite boulders. He wonders where they came from because nowhere in the
adjacent mountains is this rock type exposed. The answer is that the quartzites
were derived from a long-vanished uplift (figs. 42 and 46), carried eastward 64
by powerful rivers past the north end of the Teton Range, and then were
deposited in a vast sheet of gravel that covered much of Jackson Hole 60 to 80
million years ago. Since then, these virtually indestructible boulders have been
re-worked many times by streams and ice, yet still retain the characteristics of the
original ancient sediments.

A backward glance

So far we have seen that the Precambrian basement exposed in the Teton Range
contains a complex array of rocks of diverse origins and various ages. Before
passing on to the younger rocks, reference to our yardstick may help to place the
Precambrian events in their proper perspective.

In all of Precambrian time, which encompasses more than 85 percent of the
history of the earth (31 of the 36 inches of our yardstick), only two events are
dated in the Teton Range: the intrusion of granite and pegmatite about 2.5 billion
years ago, and the emplacement of the black dikes about 1.3 billion years ago.
These dates are indicated by heavy arrows on the time scale (fig. 30). The ancient
gneisses and schists were formed sometime before 2.5 billion years ago, and
probably are no older than 3.5 billion years, the age of the oldest rocks dated
anywhere in the world.

The close of the Precambrian—end of the beginning

More than 700 million years elapsed between intrusion of the black dikes and
deposition of the first Paleozic sedimentary rocks—a longer period of time than
has elapsed since the beginning of the Paleozic Era. During this enormous
interval the Precambrian rocks were uplifted, exposed to erosion, and gradually
worn to a nearly featureless plain, perhaps somewhat resembling the vast flat

areas in which similar Precambrian rocks are now exposed in central and eastern
Canada. At the close of Precambrian time, about 600 million years ago, the plain
slowly floundered and the site of the future Teton Range disappeared beneath
shallow seas that were to wash across it intermittently for the next 500 million
years. It is to the sediments deposited in these seas that we turn to read the next
chapter in the geologic story of the Teton Range.

65

Figure 30. A glance at the yardstick. The geologic time scale shows positions of principal events
recorded in the Precambrian rocks of the Tetons.

ABSOLUTE TIME (Years ago) INCHES

Beginning of the Paleozoic. First abundant fossils → 4
1 billion 8
Maximum age of black dikes → 10
Oldest known fossils 15
2 billion 16
Old granite and pegmatite 20
3 billion 24
Gneisses and schists formed sometime in this interval 20-27
Oldest dated rocks → 28
4 billion → 32
Minimum age of the earth 36
66

THE PALEOZOIC ERA—TIME OF LONG-
VANISHED SEAS AND THE DEVELOPMENT OF
LIFE

The Paleozoic sequence

North, west, and south of the highest Teton peaks the soaring spires and knife-
edge ridges of Precambrian rock give way to rounded spurs and lower flat-topped
summits, whose slopes are palisaded by continuous gray cliffs that resemble the
battlements of some ancient and long-abandoned fortress (fig. 31). As mentioned
previously, the cliffs are the projecting edges of layers of sedimentary rocks of
Paleozoic age that accumulated in or along the margins of shallow seas. At one
time the layers formed a thick unbroken, nearly horizontal blanket across the
Precambrian basement rocks, but subsequent uplift of the eastern edge of the
Teton fault block tilted them westward. They were then stripped from the highest
peaks.

The Paleozoic and younger sedimentary rocks in the Teton region are subdivided
into formations, each of which is named. A formation is composed of rock layers
which, because of their similar physical characteristics, can be distinguished from
overlying and underlying layers. They must be thick enough to be shown on a
geologic map. Table 2 lists the various Paleozoic formations present in and
adjacent to Grand Teton National Park and gives their thicknesses and
characteristics. These sedimentary rocks are of special interest, for they not only
record an important chapter of geologic history but elsewhere in the region they
contain petroleum and other mineral deposits.

The Paleozoic rocks can be viewed close at hand from the top of the Teton
Village tram (fig. 32) on the south boundary of the park. A less accessible but
equally spectacular exposure of Paleozoic rocks is in Alaska Basin, along the
west margin of the park, where they are stacked like even layers in a gigantic
cake (fig. 33).

Alaska Basin—site of an outstanding rock and fossil record

Strata in Alaska Basin record with unusual clarity the opening chapters in the
chronicle of seas that flowed and ebbed across the future site of the Teton 67
Range during most of the Paleozoic Era. In the various rock layers are
inscribed stories of the slow advance and retreat of ancient shorelines, of the
storm waves breaking on long-vanished beaches, and of the slow and intricate
evolution of the myriads of sea creatures that inhabited these restless waters.

Figure 31. Paleozoic rocks on the west flank of the Teton Range, air oblique view west. Ragged
peaks in the foreground (Buck Mountain on the left center, Mt. Wister, with top outlined by snow
patch on the extreme right), are carved in Precambrian rocks. Banded cliffs in the background
are sedimentary rocks. Alaska Basin is at upper right. Teton Basin, a broad, extensively farmed
valley in eastern Idaho, is at top. Photo by A. S. Post, University of Washington, 1963.

Careful study of the fossils allows us to determine the age of each formation
(table 3). Even more revealing, the fossils themselves are tangible evidence of the
orderly parade of life that crossed the Teton landscape during more than 250
million years. Here is a record of Nature’s experiments with life, the triumphs,
failures, the bizarre, the beautiful.

68

Table 2.—Paleozoic sedimentary rocks exposed in the Teton region.

Thickness Where
Age Formation (feet) Description exposed
Permian Phosphoria 150-250 Dolomite, gray, North and west
Formation cherty, sandy, flanks of Teton
black shale and Range, north
phosphate beds; flank of Gros
marine. Ventre
Mountains,
southern
Jackson Hole.
Pennsylvanian Tensleep 600-1,500 Tensleep North and west
and Sandstone, light- flanks of Teton
Amsden gray, hard, Range, north
Formations underlain by flank of Gros
Amsden Ventre
Formation, a Mountains,

domolite and red southern
shale with a Jackson Hole.
basal red
sandstone;
marine.
Mississippian Madison 1,000- Limestone, blue- North and west
Limestone 1,200 gray, hard, flanks of Teton
fossiliferous; thin Range, north
red shale in flank of Gros
places near top; Ventre
marine. Mountains,
southern
Jackson Hole.
Devonian Darby 200-500 Dolomite, dark- North and west
Formation gray to brown, flanks of Teton
fetid, hard, and Range, north
brown, black, and flank of Gros
yellow shale; Ventre
marine. Mountains,
southern
Jackson Hole.
Ordovician Bighorn 300-500 Dolomite, light- North and west
Dolomite gray, siliceous, flanks of Teton
very hard; white Range, north
dense very fine- and west
grained dolomite flanks of Gros
at top; marine. Ventre
Mountains,
southern
Jackson Hole.
Cambrian Gallatin 180-300 Limestone, blue North and west
Limestone gray, hard, thin- flanks of Teton
bedded; marine. Range and
Gros Ventre
Mountains.
Gros Ventre 600-800 Shale, green, North and west
Formation flaky, with Death flanks of Teton
Canyon Range and
Limestone

Member Gros Ventre
composed of Mountains.
about 300 feet of
hard cliff-forming
limestone in
middle; marine.
Flathead 175-200 Sandstone, North and west
Sandstone reddish-brown, flanks of Teton
very hard, brittle; Range and
partly marine. Gros Ventre
Mountains.

The regularity and parallel relations of the layers in well-exposed sections such as
the one in Alaska Basin suggest that all these rocks were deposited in a single
uninterrupted sequence. However, the fossils and regional distribution of the rock
units show that this is not really the case. The incomplete nature of this record
becomes apparent if we plot the ages of the various formations on the absolute
geologic time scale (fig. 34). The length of time from the beginning of the
Cambrian Period to the end of the Mississippian Period is about 285 million
years. The strata in Alaska Basin are a record of approximately 120 million years.
More than half of the pages in the geologic story are missing even though,
compared with most other areas, the book as a whole is remarkably complete!
During these unrecorded intervals of time either no sediments were 69
deposited in the area of the Teton Range or, if deposited, they were removed
by erosion.

Figure 32. Paleozoic marine sedimentary rocks near south boundary of Grand Teton National
Park. View is south from top of Teton Village tram. National Park Service photo by W. E. Dilley
and R. A. Mebane.

Madison Limestone
Darby Formation
Bighorn Dolomite
Gallatin Limestone

Advance and retreat of Cambrian seas: an example

The first invasion and retreat of the Paleozoic sea are sketched on figure 35.
Early in Cambrian time a shallow seaway, called the Cordilleran trough,
extended from southern California northeastward across Nevada into Utah and
Idaho (fig. 35A). The vast gently rolling plain on Precambrian rocks to the east
was drained by sluggish westward-flowing rivers that carried sand and mud into
the sea. Slow subsidence of the land caused the sea to spread gradually eastward.
Sand accumulated along the beaches just as it does today. As the sea moved still
farther east, mud was deposited on the now-submerged beach sand. In the Teton
area, the oldest sand deposit is called the Flathead Sandstone (fig. 36).

The mud laid down on top of the Flathead Sandstone as the shoreline advanced
eastward across the Teton area is now called the Wolsey Shale Member of the
Gros Ventre Formation. Some shale shows patterns of cracks that formed 70
when the accumulating mud was briefly exposed to the air along tidal flats.
Small phosphatic-shelled animals called brachiopods inhabited these lonely tidal
flats (fig. 37A and 37B) but as far as is known, nothing lived on land. Many shale
beds are marked with faint trails and borings of wormlike creatures, and a few
contain the remains of tiny very intricately developed creatures with head, eyes,
segmented body, and tail. These are known as trilobites (fig. 37C and 37D).
Descendants of these lived in various seas that crossed the site of the dormant
Teton Range for the next 250 million years.

Figure 33. View southwest across Alaska Basin, showing tilted layers of Paleozoic sedimentary
rocks on the west flank of the Teton Range. National Park Service photo.

Mount Meek
Madison Limestone
Bighorn Dolomite
Death Canyon Limestone Member
Flathead Sandstone
Precambrian Rock

As the shoreline moved eastward, the Death Canyon Limestone Member of the
Gros Ventre Formation (fig. 33) was deposited in clear water farther from shore.
Following this the sea retreated to the west for a short time. In the shallow muddy
water resulting from this retreat the Park Shale Member of the Gros Ventre
Formation was deposited. In places underwater “meadows” of algae flourished
on the sea bottom and built extensive reefs (fig. 38A). From time to time shoal
areas were hit by violent storm waves that tore loose platy fragments of recently
solidified limestone and swept them into nearby channels where they were buried
and cemented into thin beds of jumbled fragments (fig. 38B) called “edgewise”
conglomerate. These are widespread in the shale and in overlying and underlying
limestones.

71

Table 3. Formations exposed in Alaska Basin.

AGE (Numbers
show age in FORMATION
millions of years) (Thickness) ROCKS AND FOSSILS
(310)
MISSISSIPPIAN MADISON Uniform thin beds of blue-
LIMESTONE (Total gray limestone and sparse
about 1,100 feet, but very thin layers of shale.
only lower 300 feet Brachiopods, corals, and
preserved in this other fossils abundant.
section)
(345)
LATE AND DARBY FORMATION Thin beds of gray and buff
MIDDLE (About 350 feet) dolomite interbedded with
DEVONIAN layers of gray, yellow, and
black shale. A few fossil
brachiopods, corals, and
bryozoans.
(390)
(425)
LATE AND BIGHORN DOLOMITE Thick to very thin beds of
MIDDLE (About 450 feet; Leigh blue-gray or brown dolomite,
ORDOVICIAN Dolomite Member white on weathered surfaces.
about 40 feet thick at A few broken fossil
top) brachiopods, bryozoans, and
horn corals. Thin beds of
white fine-grained dolomite at
top are the Leigh Member.
(440)
(500)
LATE CAMBRIAN GALLATIN Blue-gray limestone mottled
LIMESTONE (180 feet) with irregular rusty or yellow
patches. Trilobites and
brachiopods.
(530)
MIDDLE GROS VENTRE
CAMBRIAN FORMATION

PARK SHALE Gray-green shale containing
MEMBER (220 beds of platy limestone
feet) conglomerate. Trilobites,
brachiopods, and fossil algal
heads.
DEATH CANYON Two thick beds of dark-blue-
LIMESTONE gray limestone separated by
MEMBER (285 15 to 20 feet of shale that
feet) locally contains abundant
fossil brachiopods and
trilobites.
WOLSEY SHALE Soft greenish-gray shale
MEMBER (100 containing beds of purple
feet) and green sandstone near
base. A few fossil
brachiopods.
FLATHEAD Brown, maroon, and white
LIMESTONE (175 feet) sandstone, locally containing
many rounded pebbles of
quartz and feldspar. Some
beds of green shale at top.
(570)
PRECAMBRIAN Granite, gneiss, and
pegmatite.

Figure 34. Absolute ages of the formations in Alaska Basin. Shaded parts of the scale show
intervals for which there is no record.

ENLARGED
PIECE OF
ABSOLUTE YARDSTICK
TIME SHOWN ON
STRATIGRAPHIC SCALE (Years ago) FIGURE 19
2
PALEZOIC PENNSYLVANIAN ?
300 million
MISSISSIPPIAN MADISON
DEVONIAN DARBY
3
400 million
SILURIAN
ORDOVICIAN BIGHORN
500 million 4

CAMBRIAN GALLATIN
GROS
VENTRE
FLATHEAD
600 million
PRECAMBRIAN 5

72
Figure 35. The first invasions of the Paleozoic sea.

A. In Early Cambrian time an arm of the Pacific Ocean occupied a deep trough in Idaho,
Nevada, and part of Utah. The land to the east was a broad gently rolling plain of Precambrian
rocks drained by sluggish westward-flowing streams. The site of the Teton Range was part of this
plain. Slow subsidence of the land caused the sea to move eastward during Middle Cambrian
time flooding the Precambrian plain.

B. By Late Cambrian time the sea had drowned all of Montana and most of Wyoming. The
Flathead Sandstone and Gros Ventre Formation were deposited as the sea advanced. The
Gallatin Limestone was being deposited when the shoreline was in about the position shown in
this drawing.

C. In Early Ordovician time uplift of the land caused the sea to retreat back into the trough,
exposing the Cambrian deposits to erosion. Cambrian deposits were partly stripped off of some
areas. The Bighorn Dolomite was deposited during the next advance of the sea in Middle and
Late Ordovician time.

73

Figure 36. Conglomeratic basal bed of Flathead Sandstone and underlying Precambrian granite
gneiss; contact is indicated by a dark horizontal line about 1 foot below hammer. This contact is
all that is left to mark a 2-billion year gap in the rock record of earth history. The locality is on
the crest of the Teton Range 1 mile northwest of Lake Solitude.

Once again the shoreline crept eastward, the seas cleared, and the Gallatin
Limestone was deposited. The Gallatin, like the Death Canyon Limestone
Member, was laid down for the most part in quiet, clear water, probably at
depths of 100 to 200 feet. However, a few beds of “edgewise” conglomerate
indicate the occurrence of sporadic storms. At this time, the sea covered all
of Idaho and Montana and most of Wyoming (fig. 35B) and extended
eastward across the Dakotas to connect with shallow seas that covered 74
the eastern United States. Soon after this maximum stage was reached
slow uplift caused the sea to retreat gradually westward. The site of the
Teton Range emerged above the waves, where, as far as is now known, it
may have been exposed to erosion for nearly 70 million years (fig. 35C).

The above historical summary of geologic events in Cambrian time is
recorded in the Cambrian formations. This is an example of the
reconstructions, based on the sedimentary rock record, that have been made
of the Paleozoic systems in this area.

Figure 37. Cambrian fossils in Grand Teton National Park.

A-B. Phosphatic-shelled brachiopods, the oldest fossils found in the park. Actual width of
specimens is about ¼ inch.

C-D. Trilobites. Width of C is ¼ inch, D is ½ inch. National Park Service photos by W. E. Dilley
and R. A. Mebane.

A.

B.

C.

D.

Younger Paleozoic formations

Formations of the remaining Paleozoic systems are likewise of interest
because of the ways in which they differ from those already described.

75
Figure 38. Distinctive features of Cambrian rocks.

A. Algal heads in the Park Shale Member of the Gros Ventre Formation. These calcareous
mounds were built by algae growing in a shallow sea in Cambrian time. They are now exposed
on the divide between North and South Leigh Creeks, nearly 2 miles above sea level!

B. Bed of “edgewise” conglomerate in the Gallatin Limestone. Angular plates of solidified lime-
ooze were torn from the sea bottom by storm waves, swept into depressions, and then buried in
lime mud. These fragments, seen in cross section, make the strange design on the rock. Thin
limestone beds below are undisturbed. National Park Service photo by W. E. Dilley.

The Bighorn Dolomite of Ordovician age forms ragged hard massive light-
gray to white cliffs 100 to 200 feet high (figs. 32 and 33). Dolomite is a
calcium-magnesium carbonate, but the original sediment probably was a
calcium carbonate mud that was altered by magnesium-rich sea water 76
shortly after deposition. Corals and other marine animals were
abundant in the clear warm seas at this time.

Dolomite in the Darby Formation of Devonian age differs greatly from the
Bighorn Dolomite; that in the Darby is dark-brown to almost black, has an
oily smell, and contains layers of black, pink, and yellow mudstone and thin
sandstone. The sea bottom during deposition of these rocks was foul and
frequently the water was turbid. Abundant fossil fragments indicate fishes

were common for the first time. Exposures of the Darby Formation are
recognizable by their distinctive dull-yellow thin-layered slopes between the
prominent gray massive cliffs of formations below and above.

The Madison Limestone of Mississippian age is 1,000 feet thick and is
exposed in spectacular vertical cliffs along canyons in the north, west, and
south parts of the Tetons. It is noted for the abundant remains of beautifully
preserved marine organisms (fig. 39). The fossils and the relatively pure
blue-gray limestone in which they are embedded indicate deposition in warm
tranquil seas. The beautiful Ice Cave on the west side of the Tetons and all
other major caves in the region were dissolved out of this rock by
underground water.

The Pennsylvanian System is represented by the Amsden Formation and the
Tensleep Sandstone. Cliffs of the Tensleep Sandstone can be seen along the
Gros Ventre River at the east edge of the park. The Amsden, below the
Tensleep, consists of red and green shale, sandstone, and thin limestone. The
shale is especially weak and slippery when exposed to weathering and
saturated with water. These are the strata that make up the glide plane of the
Lower Gros Ventre Slide (fig. 5) east of the park.

The Phosphoria Formation and its equivalents of Permian age are unlike any
other Paleozoic rocks because of their extraordinary content of uncommon
elements. The formation consists of sandy dolomite, widespread black
phosphate beds and black shale that is unusually rich not only in phosphorus,
but also in vanadium, uranium, chromium, zinc, selenium, molybdenum,
cobalt, and silver. The formation is mined extensively in nearby parts 77
of Idaho and in Wyoming for phosphatic fertilizer, for the chemical
element phosphorus, and for some of the metals that can be derived from the
rocks as byproducts. These elements and compounds are not everywhere
concentrated enough to be of economic interest, but their dollar value is, in a
regional sense, comparable to that of some of the world’s greatest mineral
deposits.

78
Figure 39. A glimpse of the sea floor during deposition of the Madison Limestone 330 million
years ago, showing the remains of brachiopods, corals, and other forms of life that inhabited the
shallow warm water.

A. Slab in which fossils are somewhat broken and scattered. Scale slightly reduced. National
Park Service photo by W. E. Dilley and R. A. Mebane.

B. Slab in which fossils are remarkably complete. Silver dollar gives scale. Specimen is in
University of Wyoming Geological Museum.

79

THE MESOZOIC—ERA OF TRANSITION
The Mesozoic Era in the Teton region was a time of alternating marine,
transitional, and continental environments. Moreover, the highly diversified
forms of life, ranging from marine mollusks to tremendous, land-living
dinosaurs, confirm and reinforce the story of the rocks. Living things, too,
were in transition, for as environment changed, many forms moved from the
sea to land in order to survive. It was the time when some of the most
spectacularly colored rock strata of the region were deposited.

Colorful first Mesozoic strata

Bright-red soft Triassic rocks more than 1,000 feet thick, known as the
Chugwater Formation, comprise most of the basal part of the Mesozoic
sequence (table 4). They form colorful hills east and south of the park. The
red color is caused by a minor amount of iron oxide. Mud cracks and the
presence of fossil reptiles and amphibians indicate deposition in a tidal flat
environment, with the sea lying several miles southwest of Jackson Hole. A
few beds of white gypsum (calcium sulfate) are present; they were
apparently deposited during evaporation of shallow bodies of salt water cut
off from the open sea.

As the Triassic Period gave way to the Jurassic, salmon-red windblown sand
(Nugget Sandstone) spread across the older red beds and in turn was buried
by thin red shale and thick gypsum deposits of the Gypsum Spring
Formation. Then down from Alaska and spreading across most of Wyoming
came the Sundance Sea, a warm, muddy, shallow body of water that teemed
with marine mollusks. In it more than 500 feet of highly fossiliferous soft
gray shale and thin limestones and sandstones were deposited. The sea
withdrew and the Morrison and Cloverly Formations (Jurassic and Lower
Cretaceous) were deposited on low-lying tropical humid flood plains. These

rocks are colorful, consisting of red, pink, purple, and green badland-
forming claystones and mudstones, and yellow to buff sandstones.
Vegetation was abundant and large and small dinosaurs roamed the
countryside or inhabited the swamps.

80

Table 4.—Mesozoic sedimentary rocks exposed in the Teton region.

Thickness
Age Formation (feet) Description Where exposed
CRETACEOUS
Harebell 0-5,000 Sandstone, olive Eastern and
Formation drab, silty, drab northeastern
siltstone, and dark- parts of Jackson
gray shale; thick Hole.
beds of quartzite
pebble
conglomerate in
upper part.
Meeteetse 0-700 Sandstone, gray to Spread Creek
Formation chalky white, blue- area.
green to gray
siltstone, thin coal,
and green to
yellow bentonite.
Mesaverde 0-1,000 Sandstone, white, Eastern Jackson
Formation massive, soft, thin Hole.
gray shale, sparse
coal.
Unnamed 3,500± Sandstone and Eastern Jackson
sequence of shale, gray to Hole and eastern
lenticular brown; abundant margin of the
sandstone, coal in lower 2,000 park.
shale, and feet.
coal.
Bacon Ridge 900-1,200 Sandstone, light Eastern Jackson
Sandstone gray, massive, Hole and eastern
marine, gray shale, margin of the
many coal beds. park.
Cody Shale 1,300- Shale, gray, soft; Eastern and
2,200 thin green northern parts of

sandstone, some Jackson Hole.
bentonite; marine.
Frontier 1,000 Sandstone, gray, Eastern and
Formation and black to gray northern parts
shale, marine; and south-
many persistent western margin
white bentonite of Jackson Hole.
beds in lower part.
Mowry Shale 700 Shale, silvery-gray, Gros Ventre
hard, siliceous, River Valley,
with many fish northern margin
scales; thin of the park, and
bentonite beds; southern part of
marine. Jackson Hole.
Thermopolis 150-200 Shale, black, soft, Gros Ventre
Shale fissile, with River Valley,
persistent northern margin
sandstone at top; of the park, and
marine. southern part of
Jackson Hole.
Cloverly and 650 Sandstone, light North end of
Morrison(?) gray, sparkly, rusty Teton Range and
Formations near top, underlain Gros Ventre
by variegated soft River Valley.
claystone; basal
part is silty dully-
variegated
sandstone and
claystone.
JURASSIC
Sundance 500-700 Sandstone, green, North end of
Formation underlain by soft Teton Range,
gray shale and thin Blacktail Butte,
highly fossiliferous Gros Ventre
limestones; River Valley.
marine.

Gypsum 75-100 Gypsum, white, North end of
Spring interbedded with Teton Range,
Formation red shale and gray Blacktail Butte,
dolomite; partly Gros Ventre
marine. River Valley.
Nugget 0-350 Sandstone, North flank of
Sandstone salmon-red, hard. Gros Ventre
Mountains,
southern
Jackson Hole.
TRIASSIC
Chugwater 1,000- Siltstone and North flank of
Formation 1,500 shale, red, thin- Gros Ventre
bedded; one thin Mountains, north
marine limestone end of Teton
in upper third. Range,
southernmost
Jackson Hole.
Dinwoody 200-400 Siltstone, brown, North flank of
Formation hard, thin-bedded; Gros Ventre
marine. Mountains, north
end of Teton
Range,
southernmost
Jackson Hole.
81

Drab Cretaceous strata

The youngest division of the Mesozoic Era is the Cretaceous Period. Near
the beginning of this period, brightly colored rocks continued to be
deposited. Then, the Teton region, as well as most of Wyoming, was partly,
and at times completely, submerged by shallow muddy seas. As a result, the
brightly variegated strata were covered by 10,000 feet of generally drab-
colored sand, silt, and clay containing some coal beds, volcanic ash layers,
and minor amounts of gravel.

The Cretaceous sea finally retreated eastward from the Teton region about 85
million years ago, following the deposition of the Bacon Ridge Sandstone
(fig. 40). As it withdrew, extensive coal swamps developed along the sea
coast. The record of these swamps is preserved in coal beds 5 to 10 feet thick
in the Upper Cretaceous deposits. The coal beds are now visible in
abandoned mines along the east margin of the park. Coal is formed from
compacted plant debris; about 5 feet of this material is needed to form 1 inch
of coal. Thus, lush vegetation must have flourished for long periods of time,
probably in a hot wet climate similar to that now prevailing in the Florida
Everglades.

Sporadically throughout Cretaceous time fine-grained ash was blown out of
volcanoes to the west and northwest and deposited in quiet shallow water.
Subsequently the ash was altered to a type of clay called bentonite that is
used in the foundry industry and in oil well drilling muds. In Jackson Hole,
the elk and deer lick bentonite exposures to get a bitter salt and, where the
beds are water-saturated, enjoy “stomping” on them. Bentonite swells when
wet and causes many landslides along access roads into Jackson Hole (fig.
17).

The Cretaceous rocks in the Teton region are part of an enormous east-
thinning wedge that here is nearly 2 miles thick. Most of the debris was
derived from slowly rising mountains to the west.

Cretaceous sedimentary rocks are much more than of just scientific interest;
they contain mineral deposits important to the economy of Wyoming and of
the nation. Wyoming leads the States in production of bentonite, all of 82
it from Cretaceous rocks. These strata have yielded far more oil and
gas than any other geologic system in the State and the production is
geographically widespread. They also contain enormous coal reserves, some
in beds between 50 and 100 feet thick. The energy resources alone of the
Cretaceous System in Wyoming make it invaluable to our industrialized
society.

Figure 40. The yardstick and the sea. The shaded part of the yardstick shows the 500-million-
year interval during which Paleozoic and Mesozoic seas swept intermittently across the future
site of the Tetons. When they finally withdrew about 85 million years ago, a little more than 5/8
of an inch of the yardstick remained to be accounted for.

ABSOLUTE TIME (Millions of years ago) INCHES
{submerged} 85-585 ⅝-4⅝
CENOZOIC 0-80 0-½
MESOZOIC 80-180 ½-⅞
PALEOZOIC 180-570 ⅞-4⅞
PRECAMBRIAN 570- 4⅞-

As the end of the Cretaceous Period approached, slightly more than 80
million years ago, the flat monotonous landscape (fig. 41) which had
prevailed during most of Late Cretaceous time gave little hint that the stage
was set for one of the most exciting and important chapters in the geologic
history of North America.

Birth of the Rocky Mountains

The episode of mountain building that resulted in formation of the ancestral
Rocky Mountains has long been known as the Laramide Revolution. West
and southwest of Wyoming, mountains had already formed, the older ones as
far away as Nevada and as far back in time as Jurassic, the younger ones
rising progressively farther east, like giant waves moving toward a 83

coast. The first crustal movement in the Teton area began in latest
Cretaceous time when a broad low northwest-trending arch developed in the
approximate area of the present Teton Range and Gros Ventre Mountains.
However, this uplift bore no resemblance to the Tetons as we know them
today for the present range formed 70 million years later.

Figure 41. Grand Teton National Park region slightly more than 80 million years ago, just
before onset of Laramide Revolution. The last Cretaceous sea still lingered in central Wyoming.

One bit of evidence (there are others) of the first Laramide mountain
building west of the Tetons is a tremendous deposit of quartzite boulder
debris (several hundred cubic miles in volume) derived from the Targhee
uplift (fig. 42). Nowhere is the uplift now exposed, but from the size,
composition, and distribution of rock fragments that came from it, we know

that it was north and west of the northern end of the present-day Teton
Range. Powerful streams carried boulders, sand, and clay eastward and 84
southeastward across the future site of Jackson Hole and deposited
them in the Harebell Formation (table 4). Mingled with this sediment were
tiny flakes of gold and a small amount of mercury. Fine-grained debris was
carried still farther east and southeast into two enormous depositional
troughs in central and southern Wyoming. Most of the large rock fragments
were derived from Precambrian and possibly lower Paleozoic quartzites.
This means that at least 15,000 feet of overlying Paleozoic and Mesozoic
strata must first have been stripped away from the Targhee uplift before the
quartzites were exposed to erosion.

Figure 42. Teton region at the end of Cretaceous time about 65 million years ago. The ancestral
Teton-Gros Ventre uplift had risen and prominent southeastward drainage from the Targhee
uplift was well established. See figure 41 for State lines and location map.

Remains of four-legged horned ceratopsian dinosaurs, possibly 85
Triceratops (fig. 43), reflecting the last population explosion of these
reptiles, have been found in pebbly sandstone of the Harebell Formation in
highway cuts on the Togwotee Pass road 8 miles east of the park.

Figure 43. Triceratops, a horned dinosaur of the type that inhabited Jackson Hole about 65
million years ago. Sketch by S. H. Knight.

Near the end of Cretaceous time, broad gentle uplifts also began to stir at the
sites of future mountain ranges in many parts of Wyoming. The ancestral
Teton-Gros Ventre arch continued to grow. Associated with and parallel to it
was a series of sharp steepsided elongated northwest-trending upfolds
(anticlines). One of these can be seen where it crosses the highway at the
Lava Creek Campground near the eastern margin of Grand Teton National
Park.

During these episodes of mountain building, erosion, and deposition, the
dinosaurs became extinct all over the world. The “Age of Mammals” was
about to begin.

86

TERTIARY—TIME OF MAMMALS,
MOUNTAINS, LAKES, AND VOLCANOES

Figure 44. The last inch of the yardstick, enlarged to show subdivisions of the Cenozoic Era.

STRATIGRAPHIC THE LAST INCH OF ABSOLUTE TIME
SCALE THE YARDSTICK (million years ago)
CENOZOIC
QUATERNARY

Recent and 0 0
Pleistocene
TERTIARY
Pliocene 0 0
Miocene ⅛ 12
Oligocene ¼ 25
Eocene ⅜ 40
Paleocene ⁷/₁₆ 55
MESOZOIC
CRETACEOUS ½ 65

The Cenozoic (table 1), last and shortest of the geologic eras, comprises the
Tertiary and Quaternary Periods. It began about 65 million years ago and is
represented by only the final one-half inch of our imaginary yardstick of
time (fig. 19). Nevertheless, it is the era during which the Tetons rose in their
present form and the landscape was sculptured into the panorama of beauty
that we now see. In order to show the many Tertiary and Quaternary events
in the Teton region, it is necessary to enlarge greatly the last part of the
yardstick (fig. 44). There are two reasons for the extraordinarily clear 87
and complete record. First, the Teton region was a relatively active part
of the earth’s crust, characterized by many downdropped blocks. The
number of events is great and their records are preserved in sediments
trapped in the subsiding basins. Second, the geologically recent past is much
easier to see than the far dimmer, distant past; the rocks that record later
events are fresher, less altered, more complete, and more easily interpreted
than are those that tell us of older events.

Table 5.—Cenozoic sedimentary rocks and unconsolidated deposits in the Teton region.

Thickness
Age Formation (feet) Description Where exposed
QUATERNARY
Recent
Modern stream, 0-200± Sand, gravel, and Floor of Jackson
landslide, silt along present Hole and in
glacial and streams; jumbled canyons and on
talus deposits broken rock in mountainsides
landslides and on throughout the
talus slopes; region.

debris around
existing glaciers.
Pleistocene
Glacial 0-200± Gravel, sand, silt, Floor of Jackson
deposits and and glacial Hole.
loess debris.
Unnamed 0-500 Shale, brown- Gros Ventre
upper lake gray, sandstone, River Valley.
sequence and
conglomerate.
Unnamed lower 0-200 Shale, siltstone, National Elk
lake sequence and sandstone, Refuge.
gray, green, and
red.
? Pleistocene or Pliocene
Bivouac 0-1,000 Conglomerate, Signal Mountain
Formation with purplish-gray and West Gros
welded tuff in Ventre Butte.
upper part.
TERTIARY
Pliocene
Teewinot 0-6,000 Limestone, tuff, National Elk
Formation and claystone, Refuge, Blacktail
white, soft. Butte, and
eastern margin
of Antelope Flat.
Camp Davis 0-5,500 Conglomerate, Southernmost
Formation red and gray, with tip of Jackson
white tuff, Hole.
diatomite, and red
and white
claystone.
Miocene
Colter 0-7,000 Volcanic Pilgrim and
Formation conglomerate, Ditch Creeks,

tuff, and and north end of
sandstone, white Teton Range.
to green-brown,
with locally-
derived basalt
and andesite rock
fragments.
Oligocene
Wiggins 0-3,000 Volcanic Eastern margin
Formation conglomerate, of Jackson Hole.
gray to brown,
with white tuff
layers.
Eocene
Unnamed 0-1,000 Tuff, Eastern margin
upper and conglomerate, of Jackson Hole.
middle Eocene sandstone, and
sequence claystone, green,
underlain by
variegated
claystone and
quartzite pebble
conglomerate.
Wind River and 2,000- Claystone and Eastern margin
Indian 3,000 sandstone, of Jackson Hole.
Meadows variegated, and
Formations locally-derived
conglomerate;
persistent coal
and gray shale
zone in middle.
Paleocene
Unnamed 1,000- Sandstone and Eastern margin
greenish-gray 2,000 claystone, of Jackson Hole.
and brown greenish-gray
sandstone and and brown,

claystone intertonguing at
sequence base with
quartzite pebble
conglomerate.
Pinyon 500-5,000 Conglomerate, Eastern part of
Conglomerate brown, chiefly of Jackson Hole,
rounded Mt. Leidy and
quartzite; coal Pinyon Peak
and claystone Highlands, and
locally at base. north end of
Teton Range.
88

Figure 45. Pinyon Conglomerate of Paleocene age, along the northwest margin of the Teton
Range.

During the early part of the Tertiary Period, mountain building and basin
subsidence were the dominant types of crustal movement. Seas retreated
southward down the Mississippi Valley and never again invaded the Teton

area. Environments on the recently uplifted land were diverse and favorable
for the development of new forms of plants and animals.

Rise and burial of mountains

The enormous section of Tertiary sedimentary rocks in the Jackson Hole area
(table 5) is one of the most impressive in North America. If the maximum
thicknesses of all formations were added, they would total more than 6
miles, but nowhere did this amount of rock accumulate in a single unbroken
sequence. No other region in the United States contains a thicker or more
complete nonmarine Tertiary record; many areas have little or none. The
accumulation in Jackson Hole reflects active uplifts of nearby mountains that
supplied abundant rock debris, concurrent sinking of nearby basins in 89
which the sediments could be preserved, and proximity to the great
Yellowstone-Absaroka volcanic area, one of the most active continental
volcanic fields in the United States. The volume and composition of the
Tertiary strata are, therefore, clear evidence of crustal and subcrustal
instability.

Figure 46. Teton region near end of deposition of Paleocene rocks, slightly less than 60 million
years ago. The ancestral Teton-Gros Ventre uplift formed a partial barrier between the Jackson
Hole and Green River depositional basins; major drainages from the Targhee uplift spread an
enormous sheet of gravel for 100 miles to the east. See figure 41 for State lines and location map.

The many thick layers of conglomerate are evidence of rapid erosion of
nearby highlands. The Pinyon Conglomerate (fig. 45), for example, contains
zones as much as 2,500 feet thick of remarkably well-rounded pebbles,
cobbles, and boulders, chiefly of quartzite identical with that in the
underlying Harebell Formation and derived from the same source, the
Targhee uplift. Like the Harebell the matrix contains small amounts of gold
and mercury. Rock fragments increase in size northwestward toward 90
the source area (fig. 46) and most show percussion scars, evidence of
ferocious pounding that occurred during transport by powerful, swift rivers
and steep gradients.

Figure 47. Teton region at climax of Laramide Revolution, between 50 and 55 million years ago.
See figure 41 for State lines and location map.

Conglomerates such as the Pinyon are not the only clue to the time of
mountain building. Another type of evidence—faults—is demonstrated in
figure 16. The youngest rocks cut by a fault are always older than the fault.
Many faults and the rocks on each side are covered by still younger
unbroken sediments. These must, therefore, have been deposited after fault
movement ceased. By dating both the faulted and the overlying unbroken
sediments, the time of fault movement can be bracketed.

Observations of this type in western Wyoming indicate that the Laramide
Revolution reached a climax during earliest Eocene time, 50 to 55 91
million years ago. Mountain-producing upwarps formed during this
episode were commonly bounded on one side by either reverse or thrust

faults (fig. 16B and 16C) and intervening blocks were downfolded into
large, very deep basins. The amount of movement of the mountain blocks
over the basins ranged from tens of miles in the Snake River, Salt River,
Wyoming, and Hoback Ranges directly south of the Tetons to less than 5
miles on the east margin of Jackson Hole (the west flank of the Washakie
Range shown in figure 1). The ancestral Teton-Gros Ventre uplift continued
to rise but remained one of the less conspicuous mountain ranges in the
region (fig. 47).

The Buck Mountain fault, the great reverse fault which lies just west of the
highest Teton peaks (see geologic map and cross section), was formed either
at this time or during a later episode of movement that also involved the
southwest margin of the Gros Ventre Mountains. The Buck Mountain fault is
of special importance because it raised a segment of Precambrian rocks
several thousand feet. Later, when the entire range as we now know it was
uplifted by movement along the Teton fault, the hard basement rocks in this
previously upfaulted segment continued to stand much higher than those in
adjacent parts of the range. All of the major peaks in the Tetons are carved
from this doubly uplifted block.

The brightly colored sandstone, mudstone, and claystone in the Indian
Meadows and Wind River Formations (lower Eocene) in the eastern part of
Jackson Hole were derived from variegated Triassic, Jurassic, and Lower
Cretaceous rocks exposed on the adjacent mountain flanks. Fossils in these
Eocene Formations show that it took less than 10 million years for the uplifts
to be deeply eroded and partially buried in their own debris.

The Laramide Revolution in the area of Grand Teton National Park ended
during Eocene time between 45 and 50 million years ago, and as the
mountains and basins became stabilized a new element was added.
Volcanoes broke through to the surface in many parts of the Yellowstone-
Absaroka area and the constantly increasing volume of their eruptive 92
debris was a major factor in the speed of filling of basins and burial of
mountains throughout Wyoming. This entire process only took about 20
million years, and along the east margin of Jackson Hole it was largely
completed during Oligocene time (fig. 48). However, east and northeast of
Jackson Lake a Miocene downwarp subsequently formed and in it

accumulated at least 7,000 feet of locally derived sediments of volcanic
origin.

Figure 48. Teton region near the close of Oligocene deposition, between 25 and 30 million years
ago, showing areas of major volcanoes and lava flows. See figure 41 for State lines and location
map.

The First Big Lake

Teewinot Lake (fig. 49), the first big freshwater lake in Jackson Hole, was
formed during Pliocene time, about 10 million years ago, and in it the
Teewinot Formation was deposited. These lake strata consist of more than
5,000 feet of white limestone, thin-bedded claystone, and tuff 93

(solidified ash made up of tiny fragments of volcanic rock and splinters of
volcanic glass). The claystones contain fossil snails, clams, beaver bones and
teeth, aquatic mice, suckers, and other fossils that indicate deposition in a
shallow freshwater lake environment. These beds underlie Jackson Lake
Lodge, the National Elk Refuge, part of Blacktail Butte, and are
conspicuously exposed in white outcrops that look like snowbanks on the
upper slopes along the east margin of the park across the valley from the
Grand Teton.

Figure 49. Teton region near close of middle Pliocene time, about 5 million years ago, showing
areas of major volcanoes and lava flows. See figure 41 for State lines and location map.

Teewinot Lake was formed on a down-faulted block and was dammed
behind (north of) a fault that trends east across the floor of Jackson Hole at

the south boundary of the park. Lakes are among the most short-lived of
earth features because the forces of nature soon conspire to fill them up or
empty them. This lake existed for perhaps 5 million years during middle
Pliocene time; it was shallow, and remained so despite the pouring in of a
mile-thick layer of sediment. This indicates that downdropping of the lake
floor just about kept pace with deposition.

94

Figure 50. Restoration of a middle Eocene landscape showing some of the more abundant types
of mammals. Mural painting by Jay H. Matterness; photo courtesy of the Smithsonian
Institution.

Uintatherium 6-horned, saber-toothed plant eater
Stylinodon gnawing-toothed mammal
Palaeosyops early titanothere
Helaletes primitive tapir
Sciuravus squirrel-like rodent
Smilodectes lemurlike monkey
Trogosus gnawing-toothed mammal
Hyrachyus fleet-footed rhinoceros
Ischyrotomus marmotlike rodent
Homacodon even-toed hoofed animal
Orohippus ancestral horse
Patriofelis large flesh eater
Mesonyx hyenalike mammal
Helohyus even-toed hoofed mammal
Metacheiromys armadillolike edentate
Machaeroides saber-toothed mammal
Hyopsodus clawed, plant-eating mammal
Saniwa monitorlike lizard
Crocodilus crocodile
Echmatemys turtle
95
Other lakes formed in response to similar crustal movements in nearby
places. One such lake, Grand Valley Lake (fig. 49), formed about 25 miles
southwest of Teewinot Lake; both contained sediments with nearly the same
thickness, composition, appearance, age, and fossils. Although these two
lakes are on opposite sides of the Snake River Range, the ancestral Snake
River apparently flowed through a canyon previously cut across the range
and provided a direct connection between them.

Development of mammals

The Cenozoic Era is known as the “Age of Mammals.” Small mammals had
already existed, though quite inconspicuously, in Wyoming for about 90
million years before Paleocene time. Then about 65 million years ago their
proliferation began as a result of the extinction of dinosaurs, obliteration of
seaways that were barriers to distribution, and the development of new and
varied types of environment. These new environments included savannah
plains, low hills and high mountains, freshwater lakes and swamps, and
extensive river systems. The mammals increased in size and, for the first
time, became abundant in numbers of both species and individuals. The
development and widespread distribution of grasses and other forage on
which many of the animals depended were highly significant. Successful
adaptation of herbivores (vegetation-eating animals) led, in turn, to increased
varieties and numbers of predatory carnivores (meat-eating animals).

During early Eocene time, coal swamps formed in eastern Jackson Hole and
persisted for thousands of years, as is shown by 60 feet of coal in a single
bed at one locality. Continuing on into middle Eocene time, the climate was
subtropical and humid, and the terrain was near sea level. Tropical
breadfruits, figs, and magnolias flourished along with a more temperate flora
of redwood, hickory, maple, and oak. Horses the size of a dog and many
other small mammals were abundant. Primates, thriving in an ideal forest
habitat, were numerous. Streams contained gar fish and crocodiles (fig. 50).

96

Figure 51. A typical Oligocene landscape showing some of the more abundant types of
mammals. Mural painting by Jay H. Matterness; photo courtesy of Smithsonian Institution.

Trigonias early rhinoceros
Perchoerus early peccary
Mesohippus 3-toed horse

Aepinacodon remote relative of hippopotamus
Archaeotherium giant piglike mammal
Protoceras bizarre horned ruminant
Hesperocyon ancestral dog
Hyracodon small fleet-footed rhinoceros
Poëbrotherium ancestral camel
Hypisodus very small chevrotainlike ruminant
Ictops small insect-eating mammal
Brontotherium titanothere
Protapirus ancestral tapir
Glyptosaurus extinct lizard
Hoplophoneus saber-toothed cat
Subhyracodon early rhinoceros
Merycoidodon sheeplike grazing mammal
Hyaenodon archaic hyenalike mammal
Hypertragulus chevrotainlike ruminant
97
Early in the Oligocene Epoch, between 30 and 35 million years ago,
the climate in Jackson Hole became cooler and drier, and the subtropical
plants gave way to the warm temperate flora of oak, beech, maple, alder, and
ash. The general land surface rose higher above sea level, perhaps by
accumulation of several thousand feet of Oligocene volcanic rocks (fig. 52)
rather than by continental uplift. Titanotheres (large four-legged mammals
with the general size and shape of a rhinoceros) flourished in great numbers
for a few million years and then abruptly vanished. Horses by now were
about the size of a very small modern colt. Rabbits, rodents, carnivores, tiny
camels, and other mammals were abundant in Jackson Hole, and the fauna,
surprisingly, was essentially the same as that 500 miles to the east, at a much
lower elevation, on the plains of Nebraska and South Dakota (fig. 51).

The Miocene Epoch (15 to 25 million years ago) was the time of such
intense volcanic activity in the Teton region that animals must have found
survival very difficult. A few skeletons and fragmentary parts of camels
about the size of a small horse and other piglike animals called oreodonts
comprise our only record of mammals; nothing is known of the plants.

Farther east the climate fluctuated from subtropical to warm temperate,
gradually becoming cooler toward the end of the epoch.

Fossils in the Pliocene lake deposits (8 to 10 million years old; see
description of Teewinot Formation) include shallow-water types of snails,
clams, diatoms, and ostracodes, as well as beavers, mice, suckers, and frogs.
Pollen in these beds show that adjacent upland areas supported fir, spruce,
pine, juniper, sage, and other trees and shrubs common to the area today.
Therefore, the climate must have been much cooler than in Miocene time.
No large mammals of Pliocene age have been found in Jackson Hole. The
record of life during Quaternary time is discussed later.

98

Figure 52. Layers of volcanic conglomerate separated by thin white tuff beds in Wiggins
Formation. These cliffs, on the north side of Togwotee Pass, are about 1,100 feet high and
represent a cross section of part of the enormous blanket of waterlaid debris that spread south
and east from the Yellowstone-Absaroka volcanic area. These and younger deposits from the
same general source filled the basins and almost completely buried the mountains in this part of
Wyoming.

Volcanoes

Volcanoes are one of the most interesting parts of the geologic story of the
Teton region. Although ash from distant volcanoes had settled in
northwestern Wyoming at least as far back in time as Jurassic, the first
nearby active volcanoes (since the Precambrian) erupted in the Yellowstone-
Absaroka region during the early Eocene, about 50 million years ago. From
then on, the volcanic area grew in size and the violence of eruptions and
volume of debris increased until Pliocene time. This debris had a profound
influence on the color and composition of the sediments and on the
environment and types of plants and animals.

The color of the volcanic rocks and the sediments derived from them varies
significantly from one epoch to another. For example, the middle 99
Eocene rocks are white to light-green, red, and purple, upper Eocene
are dark-green, Oligocene are light-gray, white, and brown, Miocene are
dark-green, brown, and gray, and Pliocene are white to red-brown.

Figure 53. Air oblique view south, showing the north end of the Teton Range disappearing
beneath Pleistocene lava flows. Light-colored bare area at lower left is vertical Paleozoic
limestone surrounded on three sides by nearly horizontal rhyolite lava flows. Bare slope at lower
right is west-dipping Pinyon Conglomerate, also overlapped by lava. Grand Teton is on right
skyline and Mt. Moran is rounded summit on middle skyline.

As mentioned earlier, it is probable that the vast outpouring of volcanic
rocks during late Tertiary time in the Teton region and to the north and
northeast is directly related to the subsidence of Jackson Hole and the rise of
the Tetons.

The spectacular banded cliffs of the Wiggins Formation on both sides of
Togwotee Pass (fig. 52) and farther north in the Absaroka Range are
remnants of Oligocene volcanic conglomerate and tuff that once spread as a
blanket several thousand feet thick across eastern Jackson Hole and 100
partially or completely buried the nearby older folded mountain
ranges.

Figure 54. Obsidian, a volcanic glass less than 10 million years old, especially prized by Indians
who used it for spear and arrow points and for tools.

About 25 million years ago, with the start of the Miocene Epoch, volcanic
vents opened up within, and along the borders of, Grand Teton National
Park. Major centers of eruption were at the north end of the Teton Range,
east of Jackson Lake, and south of Spread Creek. They emitted a prodigious
amount of volcanic ash and fragments of congealed lava. For example,
adjacent to one vent a mile in diameter, about 4 miles north-northeast of
Jackson Lake Lodge, is a continuous section, 7,000 feet thick, of waterlaid
strata derived in large part from this volcanic source. These sedimentary
rocks comprise the Colter Formation which is darker colored and contains
more iron and magnesium than the Wiggins Formation. The site of
deposition at this locality was a north-trending trough that represented an
early stage in the downwarping of Jackson Hole.

Pliocene volcanoes erupted in southern and central Yellowstone Park. The
volcanoes emitted viscous, frothy, pinkish-gray and brown lava called
rhyolite. This is an extrusive igneous rock that has the same composition as
granite, but is much finer grained. In several places, lava apparently 101
flowed into the north end of Teewinot Lake, chilled suddenly, and
solidified into a black volcanic glass called obsidian. Because it chips easily
into thin flakes having a smooth surface, obsidian was prized by the Indians,
who used it for spear and arrow points (fig. 54). Some of this obsidian has a
potassium-argon date of 9 million years.

Figure 55. East face of Signal Mountain showing Bivouac Formation (upper Pliocene or
Pleistocene). Tilted ledge is rhyolitic welded tuff 2.5 million years old, and slopes above and
below it are conglomerate. National Park Service photo by W. E. Dilley.

After Teewinot Lake was filled with sediment, the floor of Jackson Hole
became a flat boulder-covered surface. Nearby vents erupted heavy fiery
clouds of gaseous molten rock that rolled across this plain and then
congealed into hard layers with the general appearance of lava flows. Under
a microscope, however, the rock is seen to be made up of compressed
fragments of glass that matted down and solidified when the clouds stopped
moving. This kind of rock is called a welded tuff. One of these forms the
conspicuous ledge in the Bivouac Formation on the north and east sides of
Signal Mountain (fig. 55), and is especially important because it has a
potassium-argon date of 2.5 million years. More of this welded tuff flowed
southward from Yellowstone National Park, engulfed the north end of the
Teton Range (fig. 53), and continued southward along the west side of the
mountains for 35 miles and along the east side for 25 miles.

102

Figure 56. The final 3 million years on our yardstick of time, enlarged to show approximate
dates of major events.

THE LAST ABSOLUTE IMPORTANT EVENTS
HUNDREDTHS OF AN TIME (Years

INCH OF THE ago)
YARDSTICK
0 0 Last glaciation followed
by faulting
¹/₁₀₀₀ 50000 Second glaciation
²/₁₀₀₀ 100000 ?—First glaciation
⁶/₁₀₀₀ 700000 ?—Second Quaternary
lake
⁸/₁₀₀₀ 1 million ?—Tilting and faulting of
southern part of Jackson
Hole
¹¹/₁₀₀₀ 1.3 million ?—First Quaternary lake
¹²/₁₀₀₀ 1.5 million } Complex series of
volcanic eruptions in
southern Jackson Hole
¹⁵/₁₀₀₀ 1.9 million }
¹⁶/₁₀₀₀ 2 million ?—Development of
Hoback normal fault
²/₁₀₀ 2.5 million Eruption of welded tuff in
Bivouac Formation
²⁴/₁₀₀₀ 3 million

QUATERNARY—TIME OF ICE, MORE LAKES,
AND CONTINUED CRUSTAL DISTURBANCE
The Quaternary Period is represented by less than 15-thousandths of the last
inch on our yardstick of time (fig. 56) and the entire Ice Age takes up less
than 2-thousandths of an inch (less than the thickness of this page).
Nevertheless, the spectacular effects of various forces of nature on the Teton
landscape during this short interval of time are of such significance that they
warrant a separate discussion. The role of glaciers in carving the 103
rugged Teton peaks and shaping the adjacent valleys was mentioned
in the first part of this booklet, but is discussed in more detail here. The
magnitude and complexity of crustal movements increased during the final 2
million years of time—so much so that the beginning of Quaternary time has
not yet been identified with any single event. Figure 56 shows the major
events described below.

Hoback normal fault

The Hoback normal fault, 30 miles long, with a mile or more displacement,
developed in the southernmost part of Jackson Hole about 2 million years
ago. This fault is on the east side of the valley. Thus, the valley block was
downdropped between this fault and the Teton fault that borders the west
side.

Volcanic activity

During or shortly after major movement on the Hoback fault, and perhaps
related to it, there was a complex series of volcanic eruptions west and north
of the town of Jackson, along the south boundary of the park. In rapid

succession, lavas of many types, with a combined thickness of more than
1,000 feet, were extruded and volcanic plugs intruded into the near-surface
sedimentary rocks. These volcanic rocks can be seen on the East and West
Gros Ventre Buttes.

There are no active volcanoes in the Teton region today and no postglacial
lava flows or cinder cones. Five miles north of Grand Teton National Park
are boiling springs (Flagg Ranch hot springs) that are associated with the
youngest (late Quaternary) lavas in southern Yellowstone Park. Elsewhere in
Jackson Hole are a number of lukewarm springs but their relation to volcanic
rocks has not been determined.

What happened to the vast thicknesses of volcanic debris? We know they
existed because sections of them have been measured on the eroded edges of
uptilted folds and fault blocks. Many cubic miles of these rocks are now
buried beneath the floor of Jackson Hole, but a much greater volume was
carried completely out of the region by water, ice, and wind during the 104
final chapter of geologic history.

Preglacial lakes

Remnants of two sets of lake deposits in Jackson Hole record preglacial
events in Quaternary time. Downdropping of southern Jackson Hole along
the Hoback and Teton faults blocked the southwestward drainage of the
Snake River, and a new lake formed overlapping and extending south of the
site of the long-vanished Teewinot Lake. Incorporated in the lake sediments
are fragments of lava like that in nearby Quaternary flows. From this we
know that the lake formed after at least some of the lava was emplaced.
Apparently subsidence was more rapid than filling, for a time, at least,
because this new lake was deep. Fossil snails preserved in olive-drab to gray
fine-grained claystone overlying lava flows at the north end of East Gros
Ventre Butte are the kind now living at depths of 120 to 300 feet in Lake
Tahoe, California-Nevada. Near the margins of the lake, pink and green
claystone and soft sandstone were deposited. The duration of this lake is not
known but it lasted long enough for 200 feet of beds to accumulate.
Subsequent faulting and warping destroyed the lake, left tilted remnants of

the beds perched 1,000 feet up on the east side of Jackson Hole, and
permitted the Snake River to reestablish its course across the mountains to
the southwest.

Later downdropping of Jackson Hole impounded a second preglacial lake.
Little is known about its extent because nearly everywhere the soft brown
and gray shale, claystone, and sandstone deposited in it were scooped out
and washed away during subsequent glaciations. A few remnants of the lake
deposits are preserved in protected places, however; two are within the Gros
Ventre River Valley—one downstream from Lower Slide Lake about a mile
east of the park and the other 4 miles farther east. The latter remnant is
nearly 500 feet thick and the upper half is largely very fine grained shale and
claystone. This fine texture suggests that the lake existed for a good many
thousand years, for such deposits commonly accumulate more slowly than
coarser grained debris.

105

Figure 57. Map showing extent and direction of movement of first and largest ice sheet. See
figure 41 for State lines and location map.

The Ice Age

With the uplift of the Teton Range and the formation of Jackson Hole late in
Cenozoic time the landscape gradually began to assume the general outlines
that we see today. Rain, wind, snow, and frost shaped the first crude
approximations of the present ridges and peaks. Streams cut into the rising
Teton fault block, eroding the ancestral canyons deeper and deeper as the
uplift continued. The most recent great chapter in the story of the Teton
landscape, however, remained to be written by the glaciers of the Ice Age.

The reasons for the climatic changes that caused the Ice Age are still a matter
of much scientific debate. Various theories have been advanced that attribute
them to changes in solar radiation, changes in the earth’s orbit and
inclination to the sun, variations in the amount of carbon dioxide in 106
the atmosphere, shifts in the positions of the continents or the poles,
and to many other factors, but none has met with universal acceptance. No
doubt the explanation lies in some unusual combination of circumstances,
for widespread glaciation occurred only twice before in the earth’s history—
once in the late Precambrian and once during the Permian. It is quite clear,
however, that the glaciers did not form in response to any local cause such as
the uplift of the Teton Range, for concurrent climatic changes and ice
advance took place throughout many parts of the world.

At least three times in the last 250,000 years glaciers from the surrounding
highlands invaded Jackson Hole. The oldest and most widespread glaciation
probably took place about 200,000 years ago; it was called the Buffalo
Glaciation by Prof. Eliot Blackwelder in 1915 (see selected references). The
age estimate is based on measurements of the thickness of the decomposed
layer on the surface of obsidian pebbles in the glacial debris. Major sources
of ice were the Beartooth Mountains (fig. 1), the Absaroka Range, and the
Wind River Range. The Gros Ventre Mountains and Teton Range furnished
lesser amounts of ice.

The ice from the Beartooth and Absaroka centers of ice accumulation
converged in the northeastern part of Grand Teton National Park and flowed
south along the face of the Teton Range in a giant stream that in many places
was 2,000 feet thick (fig. 57). All but the highest parts of the Pinyon Peak
and Mount Leidy Highlands were buried and scoured. Signal Mountain,
Blacktail Butte, and the Gros Ventres Buttes were overridden and shaped by
ice at this time. Another glacier, this one from the Wind River Range, flowed
northwest along the Continental Divide, then down the Gros Ventre River
Valley, and merged with the southward-moving main ice stream west of
Lower Slide Lake. Where Jackson Hole narrows southward, the glacier
became more and more confined, but nevertheless flowed all the way
through the Snake River Canyon and on into Idaho.

107

Figure 58. Glacial deposits, outwash, and loess exposed along Boyle Ditch in Jackson Hole
National Elk Refuge. Indicated are middle Pliocene Teewinot formation (A), oldest till (B), Bull
Lake outwash gravel (C), and post-Bull Lake loess (D), which here contains snail shells dated by
Carbon-14 as 15,000 years old. Height of cliff is about 30 feet.

The volume of this great ice mass was probably considerably more than
1,000 cubic miles. When it melted, nearly all the previously accumulated
soil in Jackson Hole was washed away and a pavement of quartzite boulders
mantled much of the glaciated surface. In areas not subsequently glaciated,
the lack of soil and abundance of quartzite boulders drastically influenced
the topography, later drainage, distribution of all types of vegetation,
especially conifers and grass, and the pattern of human settlement and
industry.

108

Figure 59. View west from the Snake River overlook showing at upper right the Burned Ridge
moraine (with trees) merging southward with the highest (oldest) Pinedale outwash plain. The
next lower surface is composed of outwash from the Jackson Lake moraine which lies to the
right, out of the picture. At the bottom is Deadman’s Bar, a gravel deposit at the present river
level. Photo by H. D. Pownall.

The second glaciation, named Bull Lake, was less than half as extensive as
the first. A large tongue of ice from the Absaroka center of accumulation
flowed down the Buffalo River Valley and joined ice from the Tetons on the
floor of Jackson Hole. An enormous outwash fan of quartzite boulders
extended from near Blacktail Butte southward throughout most of southern
Jackson Hole. Glaciers in the Gros Ventre Mountains did not advance
beyond the east margin of the valley floor. Carbon-14 ages and data from
weathered obsidian pebbles suggest that this glaciation took place between
35,000 and 80,000 years ago.

Bull Lake moraines and outwash deposits are overlain directly in the
southern part of Jackson Hole by fine silt, rather than by deposits of the third
glaciation (fig. 58). This silt, of windblown origin, is called loess and

contains fossil shells dated by Carbon-14 as between 13,000 and 109
19,000 years old. Wherever the loess occurs, it is marked by abundant
modern coyote dens and badger burrows.

Figure 60. Air oblique view west toward the Teton Range, showing effects of Pinedale Glaciation
on the landscape. Mt. Moran is at top left; the mountain front is broken by U-shaped valleys
from which ice emerged into the area now occupied by Jackson Lake. The timbered area
bordering Jackson Lake is the Jackson Lake moraine. One of the braided outlet channels
breaching the Jackson Lake moraine can be seen crossing the outwash plain at the left center.
Lakes at lower right occupy “potholes” near where the 9,000-year-old snail shells occur. Snake
River is in foreground. Photo by R. L. Casebeer.

The third and last glaciation, named the Pinedale, was even less extensive
than the others. Nevertheless it was of great importance for it added the final
touches to the present landscape. The jagged intricately ice-carved peaks
(fig. 4) and the glittering lakes and broad gravelly plains are vivid reminders
of this recent chapter in geologic history.

Pinedale glaciers advanced down Cascade, Garnet, Avalanche, and Death
Canyons and spilled out onto the floor of Jackson Hole, where they built the
outermost loops of the conspicuous terminal moraines that now encircle
Jenny, Bradley, Taggart, and Phelps Lakes (fig. 13). Ice streams from Glacier

Gulch and Open Canyon also left prominent moraines on the valley floor,
but these do not contain lakes. Ice from Leigh Canyon and all of the
eastward-draining valleys to the north combined to form a large glacier in
roughly the present position of Jackson Lake. This ice entirely surrounded
Signal Mountain, leaving only the upper few hundred feet projecting as an
island or nunatak.

110

Figure 61. The Pinedale Glaciers in the central part of Jackson Hole as they might have
appeared at the time the Jackson Lake moraine was built. Solid color areas are lakes; dark
irregular pattern shows areas of moraine deposited during the maximum advance of the
Pinedale Glaciers. Pattern of open circles shows older Pinedale outwash plains; pattern of fine
dots shows outwash plains built at the time the glaciers were in the positions shown in the
drawing. Coarser dots near the margins of the glaciers represent concentrations of rock debris in
the ice.

The southernmost major advance of Pinedale ice from Jackson Lake is 111
marked by a series of densely timbered moraines that cross the Snake
River Valley. This series is collectively named the Burned Ridge moraine
(fig. 61). Extending southward for 10 miles from this moraine is a
remarkably flat surfaced gravelly outwash deposit. It was spread by streams
that poured from the glacier at the time the moraine was being built (fig. 59).
East of the Snake River, the main highway from a point just north of
Blacktail Butte to the Snake River overlook is built on this flat untimbered
surface. We assume that the outwash is younger than 15,000 years because it
apparently overlies loess of that age.

The glacier withdrew rapidly northward from the Burned Ridge moraine,
leaving behind many large irregular masses of stagnant, debris-covered ice.
The sites of these became kettles, locally known as “The Potholes” (fig. 12).
The main glacier retreated to a position marked by the loop of moraines just
south of Jackson Lake (fig. 60). Figure 61 is a sketch map showing how the
glaciers in this part of Jackson Hole might have appeared at the time the
Jackson Lake moraine was built.

Abundant snail shells have been found in lake sediments in the bottoms of
the kettles north of the Burned Ridge moraine (fig. 60) as well as on low
ridges between them. Carbon-14 age determinations indicate that the snails
lived about 9,000 years ago, either in a lake already present before the
Pinedale ice advanced and formed the Burned Ridge moraine or in ponds
that filled kettles left as the ice melted behind this moraine.

In either case, the shells indicate that the Pinedale glaciers probably existed
on the floor of Jackson Hole as recently as 9,000 years ago, at a time 112
when Indians were already living in the area. We can easily imagine
the fascination with which these primitive peoples may have watched as year
after year the glaciers wasted away, slowly retreating back into the canyons,

then withdrawing into the sheltered recesses of the high mountains,
eventually to dwindle and disappear.

Many bits of evidence, both from North America and Europe, indicate that
there was a period called the climatic optimum about 6,000 years ago when
the climate was significantly warmer and drier than at present. We suspect,
though there is as yet no direct proof, that the Pinedale glaciers wasted away
entirely during this interval.

The modern pattern of vegetation in Jackson Hole is strongly influenced by
the distribution of Pinedale glacial moraines and outwash deposits. Almost
without exception the moraines are heavily forested, whereas the nearby
outwash deposits are covered only by a sparse growth of sagebrush. This is
probably because the moraines contain large amounts of clay and silt
produced by the grinding action of the glaciers. Material of this type retains
water much better and, because of the greater variety of chemical elements,
is more fertile than the porous quartzite gravel and sand on the outwash
plains.

Modern glaciers

About a dozen small rapidly dwindling glaciers exist today in shaded
reentrants high in the Teton Range. They are probably vestiges of ice masses
built up since the climatic optimum, during the so-called “Little Ice Age.”
These glaciers, while insignificant compared to those still present in many
other mountain ranges, are fascinating working models of the great ice
streams that shaped the Tetons during Pleistocene time.

The Teton Glacier (fig. 6) is one of the best known. It is an ice body about
3,500 feet long and 1,100 feet wide that lies at the head of Glacier Gulch,
shaded by the encircling ridges of the Grand Teton, Mount Owen, and
Mount Teewinot. Ice in the central part is moving at a rate of more than 30
feet a year.

113

THE PRESENT AND THE FUTURE
The geologic story of the Teton country from the time the earth was new to
the present day has been summarized. What can we learn from it? We
become aware that events recorded in the rocks are not a chaotic jumble of
random accidents but came in an orderly, logical succession. We see the
majestic parade of life evolving from simple to complex types, overcoming
all natural disasters, and adapting to ever-changing environments. We can
only speculate as to the motivating force that launched this fascinating
geologic and biologic venture and what the ultimate goal may be. New facts
and new ideas are added to the story each year, but many unknown chapters
remain to be studied; these offer an irresistible, continuing challenge to
inquisitive minds, strong bodies, and restless, adventurous spirits.

Most geologic processes that developed the Teton landscape have been
beneficial to man; a few have interfered with his activities, cost him money,
time, effort, and on occasion, his life. Postglacial faulting and tilting along
the southern margin of Grand Teton National Park diverted drainage systems
(such as Flat Creek, southwest of the Flat Creek fault on the south edge of
the geologic map), raised hills, dropped valleys, and made steep slopes
unstable. Flood-control engineers wage a never-ending struggle to keep the
Snake River from shifting to the west side of Jackson Hole as the valley tilts
westward in response to movement along the Teton fault. Each highway into
Jackson Hole has been blocked by a landslide at one time or another and
maintenance of roads across slide areas requires much ingenuity. We see one
slide (the Gros Ventre) that blocked a river; larger slides have occurred in the
past, and more can be expected. Abundant fresh fault scarps are a constant
reminder that public buildings, campgrounds, dams, and roads need to be
designed to withstand the effects of earthquakes. Some of these problems
have geologic solutions; others can be avoided or minimized as further study
increases our understanding of this region.

Man appeared during the last one-fiftieth of an inch on our yardstick 114
of time gone by. In this short span he has had more impact on the
earth and its inhabitants than any other form of life. Will he use wisely the
lessons of the past as a guide while he writes his record on the yardstick of
the future?

115

APPENDIX

Acknowledgements

This booklet could not have been prepared without the cooperation and
assistance of many individuals and organizations. We are indebted to the
National Park Service for the use of facilities, equipment, and photographs,
and for the enthusiasm and interest of all of the park staff. We especially
appreciate the cooperation, advice, and assistance rendered by the late Fred
C. Fagergren, former superintendent of Grand Teton National Park; Willard
E. Dilley, former chief park naturalist; and R. Alan Mebane, former assistant
chief park naturalist.

Profs. Charles C. Bradley and John Montagne of Montana State University
and Bruno J. Giletti of Brown University generously provided us with
unpublished data. Cooperators during the years of background research were
the late Dr. H. D. Thomas, State Geologist of Wyoming, and Dr. D. L.
Blackstone, Jr., Chairman, Department of Geology, University of Wyoming.

Helpful suggestions were made by many of our colleagues with the U. S.
Geological Survey; S. S. Oriel, in particular, gave unstintingly of his time
and talents in the review and revision of an early version of the manuscript.
A later version had the further benefit of critical review by three other
people, all experienced in presenting various types of scientific data to
public groups: John M. Good, former chief park naturalist of Yellowstone
National Park; Bryan Harry, former assistant chief park naturalist of Grand
Teton National Park; and Richard Klinck, “1965 National Teacher of the
Year.”

We are indebted to Ann C. Christiansen, Geologic Map Editor, for advice
and guidance on the illustrations and to R. C. Fuhrmann and his staff for

preparation of many of the line drawings. Block diagrams and photo artwork
were prepared by J. R. Stacy and R. A. Reilly. All photographs without
specific credit lines are by the authors. From the beginning of the Teton field
study to editing and proofing of the final manuscript, our wives, Jane M.
Love and Linda H. Reed, have been enthusiastic and indispensable
participants.

116

Selected references—if you wish to read further

Blackwelder, Eliot, 1915, Post-Cretaceous history of the mountains of
central western Wyoming: Jour. Geology, v. 23, p. 97-117, 193-217,
307-340.
Bradley, F. H., 1873, Report on the geology of the Snake River district: U.S.
Geol. Survey Terr. 6th Ann. Rept. (Hayden), p. 190-271.
Edmund, R. W., 1951, Structural geology and physiography of the northern
end of the Teton Range, Wyoming: Augustana Library Pub. 23, 82 p.
Fryxell, F. M., 1930, Glacial features of Jackson Hole, Wyoming: Augustana
Library Pub. 13, 129 p.
——, 1938, The Tetons, interpretations of a mountain landscape: Univ.
California Press, Berkeley, Calif., 77 p.
Hague, Arnold, 1904, Atlas to accompany U.S. Geol. Survey Monograph 32
on the geology of Yellowstone National Park.
——, Iddings, J. P., Weed, W. H., and others, 1899, Geology of the
Yellowstone National Park: U.S. Geol. Survey Monograph 32, Pt. 2,
893 p.
Harry, Bryan, 1963, Teton trails, a guide to the trails of Grand Teton
National Park: Grand Teton Natural History Association, Moose,
Wyo., 56 p.
Horberg, Leland, 1938, The structural geology and physiography of the
Teton Pass area, Wyoming: Augustana Library Pub. 16, 86 p.
Hurley, P. M., 1959, How old is the earth?: Anchor Books, Garden City, N.
Y., 160 p.
Ortenburger, Leigh, 1965, A climber’s guide to the Teton Range: Sierra
Club, San Francisco, 336 p.
St. John, O. H., 1883, Report on the geology of the Wind River district: U.S.
Geol. Geog. Survey Terr. 12th Ann. Rept. (Hayden), Pt. 1, p. 173-

270.
Wyoming Geological Association, 1956, Guidebook, 11th annual field conf.,
Jackson Hole, Wyoming, 1956, Casper, Wyo., 256 p., incl. sketch
maps, diagrams, tables, and illus., also geol. map, sections, and
charts. Composed of a series of individual papers by various authors.

117

About the authors

J. D. Love, a native of Wyoming, received his bachelor and master of arts
degrees from the University of Wyoming and his doctor of philosophy
degree from Yale University. His first field season in the Teton country, in
1933, was financed by the Geological Survey of Wyoming. After 12 years of
geologic work ranging from New England to Utah and Michigan to
Mississippi, he returned to the Teton region. Beginning in 1945, he spent
parts or all of 20 field seasons in and near the Tetons. He compiled the first
geologic map of Teton County. He is the senior author of the geologic map
of Wyoming, and author or co-author of more than 70 other published maps
and papers on the geology of Wyoming. In 1961, the University of Wyoming
awarded him an honorary doctor of laws degree for his work on uranium
deposits that “led to the development of the uranium industry in Wyoming.”
The Wyoming Geological Association made him an honorary life member
and gave him a special award for his geologic studies of the Teton area. He
is a Fellow of the Geological Society of America and is active in various
other geological organizations, as well as having been president of the
Wyoming Chapters of Sigma Xi (scientific honorary) and Phi Beta Kappa
(scholastic honorary) societies.

John C. Reed, Jr., joined the U.S. Geological Survey in 1953 after receiving
his doctor of philosophy degree from the John Hopkins University. His
principal geologic work before coming to the Teton region was in Alaska
and in the southern Appalachians. Beginning in 1961, he spent five field
seasons studying and mapping the Precambrian rocks in Grand Teton
National Park, including all the high peaks in the Teton Range. He is a noted
mountaineer, a Fellow of the Geological Society of America, a member of
the Arctic Institute of North America, and the American Alpine Club. His

numerous publications, in addition to those on the Tetons, describe the
geology of mountainous areas in Alaska, the Appalachians, and Utah.

118

Index of selected terms and features

A B C D E F G H I J K L M N O P Q R S T U V W
X Y Z

Term Defined or described on page

A
amphibolite 51
anticlines 85

B
badlands 14
bentonite 81
biotite 51
brachiopods 70
Buffalo Glaciation 106
Bull Lake Glaciation 108
Burned Ridge moraine 111
buttes 18

C
Carbon-14 48
carnivores 95
chlorite 56
cirque 30
climatic optimum 112
Cordilleran trough 69

D
diabase 59
dikes 56

dipping 39
dolomite 75

E
“edgewise” conglomerate 73
epochs 46
eras 46
erosion 27
erratics 31
extrusive igneous rocks 46

F
fault 9
fault block mountain range 37
fault scarps 37
formations 66
frost wedging 25

G
geologic 10
glacial striae 30
gradients 28
Grand Valley Lake 95
granite 55
granite gneiss 54
groups 47
gypsum 79

H
herbivores 95
Hoback normal fault 103
hole 8
hornblende 51

I
Ice Age 105
igneous rocks 46
intrusive igneous rocks 46

119

J
Jackson Hole 8
jade 55

K
kettle 31

L
Laramide Revolution 82
lateral moraine 30
layered gneisses 51
Little Ice Age 112
loess 108

M
magma 60
magnetite 52
marine sedimentary rocks 21
metamorphic rocks 53
muscovite 55

N
normal fault 39
nunatak 111

O
obsidian 101
oreodonts 97
outwash 31
outwash plain 31
outwash terraces 34

P
pegmatite 56
period 46
Pinedale Glaciation 109

Q
quartzite 63

R
reverse fault 39
rhyolite 100
rock glaciers 26

S
schist 51
sedimentary rocks 45
series 47
serpentine 55
“soapstone” 55
Sundance Sea 79
systems 46

T
talus 24
Targhee uplift 83
Teewinot Lake 92
terminal moraine 30
Tetons 8
Teton fault 37
thrust fault 39
timberline 15
titanothere 97
treeline 15
Triceratops 85
trilobites 70
tuff 92

W
welded tuff 101

120

The GRAND TETON NATURAL HISTORY
ASSOCIATION
The Grand Teton Natural History Association assists the National Park
Service in the development of a broad public understanding of the geology,
plant and animal life, history, and related subjects pertaining to Grand Teton
National Park. It aids in the development of museums and wayside exhibits,
offers for sale publications on natural and human history, and cooperates
with the Government in the interest of Grand Teton National Park.

Mail orders: For a publication list, write the Grand Teton Natural History
Association, Moose, Wyoming 83012.

Creative Director: Century III Advertising. Inc.
Designer: Les Hays Studios, Inc.
Color Separations—Assembly—Plates: Orent Graphic Arts, Inc.
Type: Bodoni and Gothic
Printer: Omaha Printing Co.
Printing: Offset Lithography.
Six Colors on Covers
Two Colors on Body
121

GEOLOGIC MAP OF GRAND TETON NATIONAL PARK
High-resolution Map

EXPLANATION

CENOZOIC
QUATERNARY
Sand, gravel, and talus
Includes glacial outwash and materials deposited by present streams
Landslide deposits

Moraine deposits of Pinedale glaciers
Moraine deposits of Bull Lake and older glaciers
TERTIARY
Volcanic rocks
Lava flows and volcanic ash
Conglomerate, sandstone, shale, claystone, marl, and pumice
Deposited on land or in shallow lakes
MESOZOIC
Conglomerate, sandstone, shale, and coal
Deposited on land
Shale, sandstone, and limestone
Mostly deposited in shallow seas
PALEOZOIC
Limestone, shale, and sandstone
Deposited in shallow seas
PRECAMBRIAN
Diabase dikes
Granite, gneiss, and schist
Fault
Dashed where approximately located; dotted where concealed beneath
unfaulted younger deposits. U is on the side that moved up; D, on
the side that moved down
Geologic contact

View southwest from Lake Solitude toward the Grand Teton (right), Mt. Owen, and Mt.
Teewinot. Wyoming Travel Commission photo by J. R. Simon.

Grand Teton, Mt. Owen, and Mt. Teewinot from Jenny Lake Flat. National Park Service photo
by W. E. Dilley.

Transcriber’s Notes
Retained publication information from the printed edition: this eBook is
public-domain in the country of publication.
Corrected a few palpable typos.
Re-arranged text in captions closer to the corresponding image.
Expanded ambiguous references to illustrations, e.g. “Figure D” to
“Figure 16D”
Added one section heading, “The First Big Lake” to match the table of
contents.
Included a transcription of the text within some images, with estimated
scale readings from charts.
In the text versions only, text in italics is delimited by _underscores_.

*** END OF THE PROJECT GUTENBERG EBOOK CREATION OF
THE TETON LANDSCAPE: THE GEOLOGIC STORY OF GRAND
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