To the naked eye the only sign of geothermal activity are the 17 geothermal plants that dot the rugged landscape and the steady hum of cooling towers.
The most developed geothermal area in the state, which has 25 known geothermal areas, is The Geysers. The Geysers is a unique resource that allows power plants to use steam to run turbines and generate electricity.
�Geothermal has been around for some time now, but unlike wind and solar, it is a 24/7 resource,� said California Energy Commissioner David Hochschild.
Tapping the energy at The Geysers means wells are drilled � some as deep as two miles - to bring steam to the surface and transport it to the power plants. Water is injected to replenish the steam. The steam is later piped from wells to power plants.
Calpine Corporation operates 14 of the 17 plants at The Geysers. The California Energy Commission, which certifies thermal power plants that are 50 megawatts (MW) and larger, has jurisdiction over six of them.
The plants can produce roughly 725 MW of electricity � enough to power a city the size of San Francisco.
Four of the six Calpine facilities under the jurisdiction of the Energy Commission were among the hardest hit by last year�s Valley Fire. The fire, which killed four people and burned a total of 76,000 acres, tested the resiliency of the operations at The Geysers.
Commissioner Hochschild and other Energy Commission staff toured The Geysers recently for a firsthand look at the status of operations in the wake of the fire.
The fire caused $100 million in damages. Cooling towers were destroyed and power transmission wires, pump stations and piping were damaged.
The Geysers is almost back to full capacity. Fire-resistant cooling towers made of fiberglass replaced the burnt ones. The Geysers� power output on June 28 was 653 MW, just shy of the 685 MW produced on September 12, 2015 - the day the fire started.
Calpine officials say The Geysers is expected to be at full capacity by the end of the year.
