The authors wish to thank those of their colleagues who have assisted at various times in the preparation of this book. John Rold, Colorado State Geologist, and William Weber, of the University of Colorado Museum staff, made many helpful suggestions concerning the manuscript. John Schooland, vice president of the Colorado Historical Society, generously provided several pictures of early mining activities in Colorado. Permission to reproduce drawings and paintings of fossils and reconstructions of past environments was granted by the American Museum of Natural History and the University of Colorado Museum. Drawings, maps, and diagrams are largely the work of Robert Maurer, who also designed the cover and title page. [Illustration: Tilted dark red sedimentary rocks of the Pennsylvanian-Permian Maroon Formation are well exposed in the cliffs of Maroon Bells, southwest of Aspen. (Photo courtesy Hydraulic Unlimited Mfg. Co.)] CONTENTS _Page_ Introduction 1 I Colorado’s Three Provinces 3 The Prairies 8 The Peaks 10 Front Range 11 Wet Mountains 16 Sangre de Cristo Range and Spanish Peaks 17 Park Range and Rabbit Ears Range 19 Gore Range 20 Tenmile and Mosquito Ranges 21 Sawatch Range 22 Elk Mountains and West Elk Mountains 24 San Juan Mountains 25 Uinta Mountains 26 The Plateaus 28 II Geologic History of Colorado 32 Precambrian Era 33 Paleozoic Era 38 Cambrian Period 39 Ordovician Period 40 Silurian Period 42 Devonian Period 42 Mississippian Period 43 Pennsylvanian Period 44 Permian Period 48 Mesozoic Era 51