Exploring the World’s Largest Geothermal Plant: The Geysers

The chartered tour bus winds up the mountain, swings around switchbacks, and groans against the steep grade before pulling out on a ridgeline that workers call the North Slope, referring to how cold it gets in the winter when the wind blows. Right now the clouds rest below the tops of the surrounding mountains, dropping a mist that promises to turn into full-blown rain. Tim Conant, Calpine’s Director of Engineering, steps out of the bus first, followed by Danielle Matthews Seperas, Director of Government and Community Affairs. Both hunch their shoulders against the breeze and walk to the edge of the ridgeline. Just below, one of many geothermal power plants hums away, turning treated recycled water into electricity.

“When you flush a toilet in Clearlake Oaks, we pipe it up here and inject it,” Tim Conant explained earlier at the visitor’s center located in Middletown. He pointed at a large, lit model stretching across the wall. “We get about eight million gallons a day from Lake County and twelve and a half million from Santa Rosa.” The diagram shows how the tertiary treated recycled water gets piped into the wells, some of which descend nearly 13,000 feet into the earth. Massive pipes range all over the forty-five square miles of the complex, weaving along mountainsides, through narrow canyons, and stretched in upside-down U’s called streamlines to reach over the roadway. Once Tim explains how they work, it’s easy to see the difference between the smaller water injection pipes and larger steam pipes.

The wind has picked up a bit on the ridgeline, so everyone returns to the bus and settles in the comfortable, high-backed seats, and the tour continues. Tim’s worked at The Geysers since 1980 and carries several textbooks worth of knowledge about the place in his head. One moment he’s quoting detailed statistics about power generation, the next he’s showing the location of Black Bart’s hideout, and a minute later, he’s explaining how he drilled and injected concrete into the roadway to stabilize a section that had slid.

The bus winds around another tight corner, hugging the edge of the mountainside. A neverending maze of pipes runs alongside the road, veering off to head toward another power plant. As the bus swings left, a small gully comes into view. Steam rises from several fumaroles and the smell of sulfur fills the air. Tim and Danielle have known each other for decades and banter over facts, each talking in an easygoing, sarcastic tone. It’s clear that they love the facility—they’ve donated their time to take us on this tour. We pull over at a well, where the pipes poke out of the ground, travel twenty feet upward, and head off around the bend. Just down the hill, the fumaroles bubble; it looks like a visit to Yellowstone. A small one sits near the road. Blup, blup, blup, it sputters, spitting into the air. A sulfur-orange trail of water heads out of the bubbling pool and downhill. It’s mesmerizing.

That heated water is key to The Geysers’ success. When exposed to the high-temperature permeable rock, it transforms to superheated steam, then is piped to run the massive turbines at the power plants. We stop at one of the plants; the rain’s picked up, and the tour bus’s windows have fogged from condensation. Everyone’s required to put on a hard hat and ear protection, and for good cause. As soon as we step outside into the rain, the hum of the plant fills our ears. We move into the building, walking along the metal grating next to the three turbines spinning at 3,600 RPM. Tim stops for a moment at an old turbine sitting to the side of the power plant. It’s easily six feet tall and twenty feet long.  “Be careful touching it,” he says, pointing to the frayed edges, worn to sharp points by the high-pressure steam.

The neverending pipes don’t stop here; they head from the turbines back outdoors and into the scrubber, where the hydrogen sulfide is filtered and converted into sulfur cake. A huge bin of sulfur slowly fills, waiting to be shipped off for agricultural use. Then the pipes wind over to the cooling tower, a large structure lined with slats. Water drips on each slat, working its way down to ground level, where it will be collected and sent back down to the geothermal reservoir to be used once again. Even though it’s raining, the sound of water cascading down the slats is clearly audible, a hiss similar to standing beneath the trees in heavy rain. All these parts come together to generate enough renewable electricity to power the city of San Francisco.

The tour’s nearing the end; just one more stop at The Geysers Admin Center, an eerily empty space since Covid. Instead of a bustling building, it’s quiet, with operators sitting alone in locked rooms, monitoring every detail of the largest geothermal power plant in the world. We peer in through a window; computer screens crammed full of numbers fill the room.

After winding back down the steep mountain roads, the tour ends where it began, at The Geysers’ visitor center in Middletown. Danielle Matthews Seperas thanks everyone for coming, and people turn in their hard hats, then look through the center a bit longer before leaving, having experienced something unique.

The tour lasts three to four hours, but it goes quickly; it’s like stepping into a functional science fiction movie, a place in Lake County that’s unlike anywhere else in the world.

The Geysers will be continuing tours in 2023, but be prepared to wait six months or longer to take the trip up the mountain. For a full list of tour dates, click here. You can also find information here.

Calpine Geothermal Visitor Center

15500 Central Park Rd.

Middletown, CA 95461



Trudy and Jonah Wakefield

Started in 2018 by Trudy Wakefield, The Bloom's dedicated to showcasing all the good parts of life. If it's good news, you'll probably find it here.

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