Gray Thompson is an Emeritus Professor of Geology at the University of Montana where he taught Introductory Geology, Mineralogy, Summer Field Mapping and graduate courses in Clay Mineralogy and Shale Petrology. He has published over 20 research papers in international journals, mostly co-authored with his students. He also has authored many articles published in international climbing magazines and journals and has been the subject of other articles in these publications. Dr. Thompson is a mountaineer and professional guide with first ascents--many with Jon Turk--of peaks and routes in the Rocky Mountains, Alaska, the Yukon, Baffin Island, the Alps, the Karakoram and the Himalayas. He and Dr. Turk took many of the photographs in his texts on their climbing trips and expeditions over the last 18 years. Dr. Thompson earned a bachelor's degree in geology from Bates College, a master's in geology-geochemistry/petrology from Dartmouth College and a Ph.D. in geochemistry/clay mineralogy/petrology from Case Western Reserve University. Marc S. Hendrix is a Professor of Geology at the University of Montana in Missoula, Montana. Growing up in Gettysburg, Pennsylvania, he developed an early love of geology in the 1970s while working as a field assistant for his father, a biology professor at Gettysburg College. He earned a bachelor's degree in geology from Wittenberg University in Springfield Ohio in 1985, a master's degree in geology and geophysics from the University of Wisconsin-Madison in 1987 and a Ph.D. in applied earth sciences in 1992 from Stanford University, where he conducted research on the geologic record of mountain building and ancient climate in western China. As a postdoctoral researcher at Stanford, he analyzed the geologic history of Mongolia. In 1994 Dr. Hendrix joined the faculty at the University of Montana where he has developed a field-based research program focused on the geology of the northern Rocky Mountains. He and his students have published a variety of technical papers on the geology of North America, Asia and Africa, and in 2011 he authored and illustrated GEOLOGY UNDERFOOT IN YELLOWSTONE COUNTRY. Dr. Hendrix has served as an expert witness and consultant in the field of geology, and he continues to travel broadly to conduct geologic research. He lives in Missoula with his wife and two sons.