A hundred and seventy years after the gold rush, California is in the grip of “white gold” fever as the race heats up to develop new, environmentally friendly sources of lithium to meet surging demand for electric-car batteries.

Deep below the Salton Sea, a polluted, shrinking lake in Southern California, waters superheated by the rocks beneath the earth’s surface contain large amounts of dissolved lithium that, if they can be commercially extracted, could help power the electric-vehicle (EV) revolution.

The California Energy Commission estimates the area could produce 600,000 tons of lithium carbonate annually, worth $7.2 billion. That would comfortably meet current global demand for the metal, which is used in batteries for cell phones and laptops, and to store grid electricity, as well as for cars.

“It’s the single largest lithium brine resource in the United States, if not on the planet…It will be a critical hub,” said Rod Colwell, CEO of Australian firm Controlled Thermal Resources, one of several companies planning to extract lithium from the thermal waters below the Salton Sea.

The plan is to harvest lithium as a by-product of geothermal power generation, which uses the earth’s natural heat to make electricity. At geothermal plants, wells are drilled into reservoirs deep underground to tap very hot water or steam that is used to drive turbines and generate power.

The geothermal fluids, called brines, can reach temperatures as high as 572°F (300°C) underground, dissolving lithium and other metals from rocks. As well as using the heat from the fluids to generate power, Controlled Thermal Resources aims to extract lithium from the fluid before re-injecting it into the ground.

The company says the technique, called direct lithium extraction, produces negligible carbon dioxide emissions and eliminates the need for traditional carbon-intensive open-pit mining or evaporation ponds, which use vast quantities of water.

Imperial Valley, adjoining the Salton Sea, has already been dubbed “Lithium Valley,” as hopes rise that the area could develop into an integrated battery manufacturing hub, lifting the economically depressed region.

And it’s not only in California. In the U.K., Germany, and elsewhere, countries are hunting for new environmentally friendly sources of lithium, to lessen their dependence on imports of the critical metal known as “white gold.” The search is being driven by the growing focus on investment in companies with good environmental, social responsibility, and corporate governance records (ESG).

“We are going to need a lot more lithium—and quite soon actually—to achieve even modest electrification goals of say 10% EV penetration per year,” said Chris Berry, president of House Mountain Partners, a Washington, D.C., strategic metals consultancy.

In Cornwall, the picturesque southwest corner of Britain where U.S. President Joe Biden and other leaders of the Group of Seven economies gathered Friday to discuss a green recovery from the COVID pandemic and strengthening global supply chains, there are also plans afoot to revive the region’s ancient mining industry by producing lithium.

“Europe currently produces no battery-grade lithium at all from domestic raw materials. If Europe and the U.K. do not secure domestic supplies of lithium, then they will be held hostage to getting that from somewhere else. Complacency is no longer appropriate,” Jeremy Wrathall, CEO of Cornish Lithium, told Fortune.

In a similar way to the Salton Sea project, Cornish Lithium aims to exploit the “significant potential” for lithium-enriched geothermal waters under Cornwall, pumping the waters to the surface and using geothermal energy to extract lithium compounds. Cornish Lithium is also looking into the potential to extract lithium from mica minerals in granite in Cornwall.

In Germany, home to Europe’s biggest auto industry, Vulcan Energy Resources wants to produce lithium in another geothermal project in the Upper Rhine Valley. The first phase, scheduled to start in 2024, would require investment of 700 million euros ($850 million) for geothermal wells and lithium extraction plants.

Berry said geothermal projects involved some technology risk that needed to be “worked through before we know for sure that this is a viable, commercial-scale source.”

“I’m pretty optimistic…I think it’s a good route to pursue,” he said.

After several years of decline, lithium prices have rebounded sharply this year, to around $13.75 per kilogram of lithium hydroxide. Berry points out that lithium is not rare—in fact it could be extracted from sea water if it was economically viable—but he predicts the market will be “very, very tight” to 2025.

Lithium demand, currently about 370,000 tons of lithium carbonate a year, is set to nearly triple to about a million tons by 2025 and then to double again to 2 million tons annually by 2030, he says.

Worldwide production of electric vehicles is set to grow from 3.4 million in 2020 to 12.7 million in 2024, according to analytics company GlobalData. Research firm Rystad Energy predicts a “global frenzy” to beef up the world’s lithium-ion battery manufacturing capacity, with $560 billion of investment needed by 2030 to meet surging demand.

For now, the only lithium production in the United States is from a brine operation in Nevada. Plans for new open-pit lithium mines in Nevada have run into legal challenges and opposition from environmentalists, but Energy Secretary Jennifer Granholm praised the proposals to extract lithium from geothermal brine at the Salton Sea June 11 as “utterly sustainable” and “very exciting,” the Associated Press reported.

Australia is the world’s biggest producer of lithium, mining the metal from hard rock in an energy-intensive process. Add in the impact of shipping the concentrate to China for refining, and nine tons of carbon dioxide are emitted for every ton of lithium carbonate produced, according to commodity research firm Roskill, which forecast last year that CO2 emissions from lithium production would triple by 2025.

Another important source of the metal is the “lithium triangle” of Argentina, Bolivia, and Chile, where underground brine is pumped into ponds and left for months, or even years, to evaporate in the sun, leaving behind lithium. The process uses huge amounts of groundwater in one of the world’s driest regions. In Chile’s Salar de Atacama salt flat, lithium and other mining activities consumed 65% of the water, causing groundwater depletion and soil contamination and forcing local communities to abandon ancestral settlements, the UN said last year.

At the Salton Sea, Controlled Thermal Resources plans to open a 50-megawatt geothermal power station in September 2023 and a 20,000 ton per year lithium hydroxide facility in the first quarter of 2024, Colwell told Fortune. The company is working with Oakland-based startup Lilac Solutions, which has developed a new, more efficient ion exchange technology to extract lithium. Breakthrough Energy Ventures, whose investors include Microsoft cofounder Bill Gates, Amazon’s Jeff Bezos, and media magnate Michael Bloomberg, led a $20 million funding round for Lilac Solutions last year.

BHE Renewables, a subsidiary of Warren Buffett’s Berkshire Hathaway, which owns 10 geothermal power plants in the Salton Sea area, is also working on a project to recover lithium from geothermal brine.

Controlled Thermal Resources’ Colwell said that after eight years of working on his project, “the stars are finally aligning.”

“The compound growth rate for EV sales every month is just exceeding every previous forecast, so we seem to have some momentum now finally that hopefully will break through,” he said.