The Hot Springs Bay Valley (HSBV) geothermal resource area on Akutan Island, Alaska, has been exploredsince 2009. Geological, geochemical, geophysical surveys and the drilling of two thermal gradient wellssuggest a mature neutral-chloride reservoir between 240 and 300◦C, with outflow temperatures ∼180◦C. A network of regional and local structures control near-surface permeability. Alteration, mineralizationand geophysical patterns, including high-temperature hydrothermal minerals at unexpectedly shallowdepths of formation, indicate a poorly to moderately developed clay cap, likely the result of erosion ofthe upper portion of an older, well developed system.