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

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.

Part 2

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.

Continue reading Creation of the Teton Landscape: the Geologic Story of Grand Teton National Park free in the Wunder reader →