An appraisal investigation of the geothermal resources of a portion of the Lower Colorado River Region of the U.S. Bureau of Reclamation is reported. The study area includes most of Arizona, part of western New Mexico west of the continental divide, and a small part of southwestern Utah. Almost 300 water samples have been collected from the study area and chemically analyzed. These samples include hot wells and springs in addition to nearby nonthermal waters to help establish background chemistry. Further, almost 10,000 chemical analyses of groundwaters were obtained from the U.S. Geological Survey's water quality file. Routine geothermal interpretative techniques were then applied to these chemical data to identify geothermal anomalies which might indicate the presence of exploitable geothermal resources. These geochemical anomalies were then evaluated in terms of available geophysical data such as heat flow, gravity, magnetics, basement linears, earthquake epicentral locations, depth of sedimentary basins, quaternary volcanics, recent fault scarps, etc. to further delineate the size and shape of the prospective geothermal sites and help establish their production potential.