Our studies and those of our colleagues in Idaho indicate that the western Snake River Basin is a major geothermal province, similar in some ways to the Imperial Valley Geothermal Province. Deep drilling should encounter high temperature fluids in permeable rocks below 2 km and at shallower depths where permeability has developed, as along faults and fracture zones. The Cow Hollow area seems to have the necessary conditions for a high-temperature geothermal reservoir: high heat flow, permeable rocks at depth, and a barrier to migration or trap. Prior to drilling a deep exploratory well, more geologic and geophysical work and more detailed structural geologic studies should be done, more heat-flow holes should be drilled, and additional gravity and magnetic surveys should be done. In addition, some geochemical electrical resistivity, and seismic studies should be made to further define the anomaly. After these more definitive investigations are made, the only sure method of determining if geothermal fluids exist in commercial quantities is to drill enough wells to define the base temperature and production capabilities of the reservoir.