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? [Illustration: Signature] 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_