Geothermal energy is produced by the heat of the earth and is often associated with volcanic and seismically active regions. California, with its location on the Pacific "Ring of Fire," has 25 known geothermal resource areas, 14 of which have temperatures of 300 degrees Fahrenheit or greater. Forty-six of California's 58 counties have lower temperature resources for direct-use geothermal. In fact, the City of San Bernardino has developed the largest geothermal direct-use projects in North America, heating 37 buildings -- including a 15-story high-rise and government facilities -- with fluids distributed through 15 miles of pipelines. Environmentally benign fluids are discharged to surface water channels after heat is used.

When added together, California's geothermal power plants produce about 40 percent of the world's geothermally generated electricity. The power plants have a dependable installed capacity of about 1,900 megawatts -- producing 4.9 percent of California's total electricity in 1999 (12,786 million kilowatt/hours).

The most developed of the high-temperature resource areas of the state is the Geysers (a photo of a Geysers' power plant's Unit # 18 is shown to the right). Located north of San Francisco, the Geysers was first tapped as a geothermal resource to generate electricity in 1960. It is one of only two locations in the world where a high-temperature, dry steam is found that can be directly used to turn turbines and generate electricity (the other being Larderello, Italy).

Other major geothermal locations in the state include the Imperial Valley area east of San Diego and the Coso Hot Springs area near Bakersfield. It is estimated that the state has a potential of more than 4,000 megawatts of additional power from geothermal energy, using current technologies.

Additionally, two forms of geothermal energy -- Hot Dry Rock and Magma -- have the potential to provide thousands of megawatts in California. Investigations in Hot Dry Rock were focussed in the Clear Lake area of Lake County; Magma research occurred in the Long Valley Caldera of Mono County.