Robert H. Webb is a research hydrologist with the U.S. Geological Survey in Tucson. He is the author of Grand Canyon: A Century of Change: Rephotography of the 1889-1890 Stanton Expedition (University of Arizona Press, 1996) and is coeditor or coauthor of a number of other books, including Cataract Canyon: A Human and Environmental History of the Rivers in Canyonlands (University of Utah Press, 2004), which he wrote with Jayne Belnap and John S. Weisheit.