The Renewable Energy Atlas of the West has overview maps of geothermal resources and facilities in the Western U.S. Look here for a big-picture overall sense of where the best resources are located. More detailed geothermal resource maps have been developed by the INEEL as part of the GeoPowering the West program.
The Geo-Heat Center has identified 271 communities in the Western United States with geothermal resources that could support geothermal direct-use (although not necessarily geothermal electricity). This analysis includes communities within 8 km of a 50 degree C resource. As noted above, electricity generation generally requires 100 degree C resource. This Center also has a nice interactive map showing where geothermal power plants are located.
An excellent database, pulling together much of what has been found by various test and exploratory wells in the Western U.S., has been compiled by Southern Methodist University. This database is very detailed and technical, and thus not for casual perusing. The web site however also has several summary maps, along with instructions on how to use the database.
