Geothermal Power Plant in Imperial County, California. The Leathers geothermal power plant is located in the Salton Sea (geothermal resource area) located in southeastern California (just 60 miles east of San Diego). It is part of the Imperial Valley Partnership Project and is under contract to sell power to Southern California Edison Company under a 30 year power purchase agreement. The combined capacity at Imperial Valley is about 268 net MW (nominal). In 2010, the United States led the world in geothermal electricity production with 3,086 MW of installed capacity from 77 power plants. The largest group of geothermal power plants in the world is located at The Geysers, a geothermal field in California.