The Geology and Earth Resources Division (the Washington Geological Survey) provides geologic information to government, industry, and individuals to encourage and aid in the prudent development of the state's geothermal energy resources, inventories, and documents.
With few exceptions, the higher-temperature geothermal areas in Washington occur in the Cascade Range. A large “low”-temperature zone also occurs in the Columbia Basin in Eastern Washington.
Washington’s geothermal potential for generating power has not had a lot of study. However, the Geology and Earth Resources Division has published Geologic Map GM-25 (Korosec and others, 1981) which is a 1:500,000-scale map showing the distribution of thermal (at or above 20°C or 68°F) springs and wells in the state and a tabulation of basic information about them. GM-25 reported on 31 thermal springs, 29 mineral springs, and 338 thermal wells. The thermal and mineral springs are, for the most part, located in the Cascade Range, and many are associated with stratovolcanoes. Most of the thermal wells are located in the Columbia Basin. In 1994, three thermal springs and 603 thermal wells were added to the inventory.
Interactive Map: The Washington State Geologic Information Portal has a geothermal resources layer that will allow you to make your own map of the area you are interested in.
Christie, Rebecca A., compiler; rev. by Walkling, Lee, 2009, Bibliography and index of geothermal resources and development in Washington State, with selected general works: Washington Division of Geology and Earth Resources Open File Report 2009-2, 90 p. [http://www.dnr.wa.gov/Publications/ger_ofr2009-2_geothermal_bib.pdf]
Korosec, Michael A.; Kaler, Keith L.; Schuster, J. E.; Bloomquist, R. G.; Simpson, S.; Blackwell, D. D., compilers, 1981, Geothermal resources of Washington: Washington Division of Geology and Earth Resources Geologic Map GM-25, 1 sheet, scale 1:500,000. [http://www.dnr.wa.gov/Publications/ger_gm25_geothermal_res_wa_500k.pdf]
Sjoding, Dave; Hamemyik, Erin; Norman, D. K., 2009, Washington geothermal energy status and roadmap; Second working draft: Washington State University Extension Energy Program, 1 v. [http://www.energy.wsu.edu/Documents/WashingtonGeothermalEnergyStatusAndRoadmap.pdf]