John Rold, Colorado State Geologist, assisted in coordinating our efforts at the beginning of this study. Lou Campbell, State Cartographer, gave valuable advice and assistance throughout the effort. Wallace Hansen and James Blakey of the USGS Geologic and Water Resources Divisions, respectively, read the final manuscript and helped in many other ways. Joanna Trolinger served as research assistant and manuscript typist. Many others in the USGS, SCS, and other organizations helped in supplying information and advice. Tom Bates, then Chairman of the USGS Central Region Earth Science Applications Task Force, was the originator of the study, leader of the USGS participation effort, and guiding inspiration throughout.