Salton Sea Power Station

This cluster of seven geothermal plants is the largest of three major geothermal energy production sites in the Imperial Valley. A network of deep wells drilled in the geothermal field allow water, heated by the earth's mantle, to come to the surface and to power electrical generators. Owned by the CalEnergy Company, the electricity is sold to the local power utility and put on the grid. The seven plants in this field produce enough electricity to power over 100,000 homes.

See also: http://en.wikipedia.org/wiki/Salton_Sea_Power_Station