North of San Francisco in the Mayacamas Mountains, Sonoma County has been harnessing geothermal power for decades at Calpine Corporation's Geysers facility. The largest of its kind in the world, this facility is an operation of 15 power plants that generate 725 megawatts (MW) of baseload power for California’s power grid - enough to power a city the size of San Francisco. The Geysers provide 24 percent of California’s renewable energy, 40 percent of America’s geothermal power. Furthermore, eight millions of recycled wastewater are currently used to recharge naturally-occurring steam reservoirs beneath the earth’s surface.
In 2009, California produced 13,023 gigawatt-hours (GWh) of energy using geothermal resources, more than any other renewable resource except hydropower.