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Casa Diablo Hot Springs and Geothermal Facility, Long Valley Caldera, California

The Casa Diablo Hot Springs site is located on the southwestern edge of the resurgent dome along a major fault system. The fault forms the east side of the down-dropped block that transects the resurgent dome. This down-dropped block is called the medial graben. Three binary-cycle generators built here in 1985 and 1990 produce about 45 megawatts of electricity. Wells, each about 200 m deep, supply the powerplants with 170o water. Heat exchangers transfer the thermal energy from the water to isobutane, which vaporizes and drives turbine generators.