The Eastern San Juan Mountains: Their Ecology, Geology, and Human History

1. A Legacy of Mountains Past and Present in the San Juan Region

Preface x not an easy read and may require background study. Because of the use of technical language, a general glossary is included at the end of the book. The purpose of these two volumes is to inform residents, researchers, educators , and visitors about the workings of a complex mountain system. Thus geology, ecology, climate, hydrology, and human activity are addressed. Neither the western volume nor this text is considered an “end-all” reference to this magnificent mountain range. Indeed, it is our objective to challenge the reader toward a greater understanding of complex mountain systems and to stimulate further research. As a consequence of the success of the western volume, the nonprofit Mountain Studies Institute (MSI) was established in 2002, headquartered in Silverton, Colorado. In 2008 the MSI, along with Fort Lewis College and the University of Colorado, joined together to form the San Juan Collaboratory, dedicated to the study of the San Juan Mountains and other mountain systems. The editors and authors of this book volunteered their time and their own expense to assemble this text. As with the western volume, the royalties generated will be donated to the San Juan Mountains Undergraduate Research Fund, which provides economic assistance to students conducting research associated with this mountain range. xi Inadditiontothetwenty-eightcontributorstothistext,numerous other people behind the scenes have contributed to this publication through reviews, edits, time provided, and donated images. If we miss anyone, please accept our apologies. We especially thank these reviewers: Cathy Ager, Olivier Bachmann, Kip Bossong, Peter Brown, Jeff Coe, Cathy Cripps, Skip Cunningham, Emmett Evanoff, Allen Farnsworth, Tony Gurzick, Shaul Hurwitz, David Jamieson, Donald E. Kendall, Bob Kirkham, Joe Lewandowski, Vince Mathews, Robert Mathiasen, John M. Smethurst III, Donna M. Steele, and Jim White. We are particularly indebted to the anonymous reviewers provided by the University Press of Colorado who gave us insight and allowed us to improve the final product. Mark Williams, in association with the San Juan Collaboratory, was instrumental in providing funds for color photo reproductions. The editors are keenly aware that errors might have occurred, and we accept ultimate responsibility for such oversights. But like other publications of a scientific nature, we view this text as a stepping stone to better understanding and treat it as a current “progress” report. Acknowledgments The Eastern San Juan Mountains Part1 PhysicalEnvironmentoftheSanJuanMountains  Throughout time, people have been drawn to mountains for inspiration , recreation, and scientific exploration. Mountains are also vast warehouses of natural resources and libraries of geologic history. Mountains form in response to the dynamic forces of our planet. The life spans of mountain belts, from initial uplifts to erosion to base levels, run from tens of millions to hundreds of millions of years. Ancient and active mountain belts are part of the fabric of continental crust and provide clues to events that build and reshape continents. The concept of plate tectonics (Condie 1989) provides a framework within which to investigate and explain mountain building. (For a summary of plate tectonics, refer to The Western San Juan Mountains, chapter 2.) The San Juan Mountains are part of the extensive Southern Rocky Mountains (figure 1.1) and are dominated by some of the highest and most jagged summits in the continental United States. The San Juans reveal a fascinating geologic story of the creation and demise of many mountain ranges in this region during the past 1.8 billion years, including probable current uplift from active mountain-building processes. The history of any mountain belt is deciphered from its modern landscape and the remaining rock record. An understanding of the geologic evolution of the San Juan Mountains comes from many studies done over the past 125 years. Field ALegacyofMountainsPastandPresent intheSanJuanRegion C h a p t e r o n e DavidA.GonzalesandKarlE.Karlstrom David A. Gonzales and Karl E. Karlstrom  studies of rocks exposed in the region are supported by satellite images, geophysical probes of the deep earth, measurements of rock ages, and analyses of rock compositions . These data give geologists the ability to reconstruct the geologic history in Figure 1.1 Physiographic provinces of the Four Corners region showing the extent of the Colorado Plateau and the Southern Rocky Mountains. From http://www2. nature.nps...