Demolition of cement plant begins at historic Cupertino quarry

Construction crews this week begin work to demolish and remove a sprawling cement plant at a historic quarry in the hills west of Cupertino that has provided building materials for dams, highways, bridges and other projects across California since the 1930s, but in recent years encountered growing environmental violations and opposition from neighbors.

Workers will remove roughly 40 structures across 123 acres at the Permanente Quarry, a job that will take two years, according to officials at Heidelberg Materials North America, a German company with U.S. headquarters in Irving, Texas, that owns the site.

Planned for demolition are massive conveyor belts, silos, mills, warehouses, offices and even the huge cement kiln that heated rock to 2,700 degrees.

“It's essentially the entire plant,” said Gregory Ronczka, vice president of environmental projects for Heidelberg Materials North America.

“Some of the reinforced concrete buildings will take a lot more effort to get done since they are going to be hammering away and pulling out rebar,” he said. “The cement silos are reinforced concrete. Other buildings are wood-frame with sheet metal siding. Those will go down pretty quick.”

The company owns 3,510 acres around the quarry, an area three times the size of San Francisco's Golden Gate Park.

Although mining operations on the property date back to 1902, more modern facilities were established by industrialist Henry J. Kaiser in 1939. In recent decades, the quarry produced more than half the cement used in the Bay Area and 70% of the cement used in Santa Clara County.

Its cement built Shasta Dam at California’s largest reservoir, Shasta Lake near Redding, along with Highway 101, Highway 85 and other major Northern California landmarks.

But the facility also became one of the Bay Area's largest polluters, ranking at or near the top of Bay Area industrial sites for emissions of greenhouse gases and airborne mercury.

Neighbors in the Cupertino and Palo Alto foothills opposed Kaiser’s plans to expand operations as far back as the 1930s, fearing that dust and pollution from the open-pit mine and cement plant would pollute farms and orchards. As rural areas became suburbs and the population grew with the rise of Silicon Valley, neighborhood opposition increased. The company also ran afoul of tightening environmental laws.

The facility, which used to be called the Lehigh quarry, closed in 2020 during the COVID pandemic when worldwide demand for building materials dropped. After Santa Clara County officials opposed plans to allow expanded operations until 2050, Heidelberg, which owns 10 cement plants in North America, shut it down.

“The quarry was down to the last few years of reserves anyway,” Ronczka said. “Some of the equipment dates back to 1939. Some parts of the plant were upgraded in 1979. But that's very old. It didn't make financial sense to bring up a plant that old. It was a business decision.”

In 2023, Heidelberg signed an agreement with the Santa Clara County Board of Supervisors to shutter the cement plant for good.

Under state and federal law, the company must fill in the massive quarry. That could take 30 to 40 years, according to a reclamation plan the company filed in 2024 with Santa Clara County officials.

“Part of it was market forces - the old quarry was played out,” said Joe Simitian, a former Santa Clara County supervisor who opposed the quarry’s expansion. “And part of it was an indication by the county that an expansion was not going to happen.”

Simitian, now a visiting fellow at Stanford University, said he would like most of the land to eventually become open space, perhaps run by the Midpeninsula Regional Open Space District, an agency that owns the adjacent Rancho San Antonio Open Space Preserve.

Simitian said the demolition of the cement plant is an important chapter in the history of the site.

“It's been a long time coming,” he said. “It will take not just months or years but decades before the site is fully reclaimed. It's a long goodbye. But the demolitions are proof positive that it is real and the time has finally come. That's heartening.”

Heidelberg will spend millions to demolish the cement plant and gradually fill in the 550-foot-deep open-pit limestone mine. It can charge other companies to accept rock and soil from construction projects. One such project, Ronczka said, could be plans to dig a massive tunnel under downtown San Jose to extend BART service to the area.

The company’s reclamation plan estimates that 43 million cubic yards of material will be needed to fill the quarry. That’s enough to fill about 4.3 million typical-sized dump trucks. The company says it has about a quarter of that material, or 12 million cubic yards, on the site, as waste rock that was never processed. It will need to import 31 million more.

One nearby example: A former quarry in Fremont near the San Francisco Bay shoreline, the Dumbarton Quarry, was converted over 14 years into a new public campground that opened in 2021 as part of the East Bay Regional Park District. That former gravel pit was 320 feet deep and in operation from the 1950s until 2007.

Heidelberg has also left open the possibility of using some of the flatter land closer to existing Cupertino neighborhoods to build new homes.

"We haven't had those discussions with the county or the city yet,” Ronczka said. “There will be some listening sessions.”

Heidelberg has signed a deal with another firm, Vulcan Materials, based in Alabama, to crush and sell aggregate rock from the quarry that was blasted out but not used, to other companies, he said. That work is ongoing and could continue for 10 or 15 years.

left in nearby Permanente Creek

Environmentalists noted the facility had hundreds of violations of local, state and federal air and water rules. One issue is how to fill the quarry pit in the coming decades with the least amount of noise, pollution and disruption to the surrounding neighborhoods.

“We're glad the quarry operations have stopped,” said Alice Kaufman, policy director of Green Foothills, a Palo Alto environmental group. “They were pretty environmentally harmful. We're hoping the property can be restored to open space - the way it should be. But there are still a lot of unanswered questions.”

Company officials say Bay Area residents are still going to use cement. But it may come from other parts of the world, where there are fewer environmental standards.

“A lot of people don't realize it,” Ronczka said. “But that area is going to get cement one way or the other - and that probably means imports on ships traveling from Turkey or Vietnam or other places. That's kind of a sad story, unfortunately.”

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This story was originally published July 10, 2026 at 3:53 PM.