Part 1

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._

_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

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

_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. Go and look behind the Ranges— Something lost behind the Ranges. Lost and waiting for you. Go._” KIPLING—_THE EXPLORER_

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 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 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.

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 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 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.

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.

Figure 3. _The Teton landscape as seen from Signal Mountain._

Three steepsided hills called _buttes_ rise out of the flat floor of Jackson Hole. 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 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._—