Its scenic hills and ridges loom over San Jose. But its legacy looms over all of California. Today, Almaden Quicksilver County Park is an oasis of wildlife and recreation, a 4,200-acre preserve on the southern edges of San Jose’s Almaden Valley neighborhood where thousands of harried urban residents relax every year by hiking, mountain biking or riding horses.

But starting in the 1850s, long before Santa Clara County was known for computers or even orchards, thousands of people from the United States, Mexico, China and England descended on the Almaden Hills here, where the mercury they dug up helped fuel California’s Gold Rush in the Sierra Nevada by allowing gold to be separated from ore.

“They could not have run the Gold Rush without us,” said Terri Sanislo, a park interpreter with the Santa Clara County Parks and Recreation Department. “We were the only place on this side of the world that could produce mercury in the quality and the quantity needed for the Gold Rush.”

At the peak in the 1870s, there were seven mines and up to 3,000 residents, with Cornish tin miners and their families living in “Englishtown,” and Mexican miners living nearby in “Spanishtown.” The area was featured in Wallace Stegner’s 1972 Pulitzer Prize-winning novel “Angle of Repose.”

The New Almaden Mines became the largest mercury mines in North America in the mid-19th century, putting the young city of San Jose on the map and giving its newspaper, just the San Jose Mercury back then, a name. But the mines also left a hazardous legacy that is still being cleaned up.

Visitors to the park – famous for its wildflowers every April and May – can see occasional pieces of rusting mining equipment, sites of old furnaces and a prominent brick chimney, along with interpretive signs. And there is the New Almaden Quicksilver Mining Museum, at 21350 Almaden Road, on the park’s northern edge, a favorite of school tour groups and curious passersby.

Along the area’s creeks and reservoirs are signs warning people not to eat the fish. Because of the mining, and the naturally occurring levels of mercury in the soil, some fish species have built up high levels of the metal – a toxin that, ingested in high levels, can impair physical coordination, decrease brain function, blur vision and damage the kidneys.

Most mercury mining in the area wound down around World War I, but some continued until 1975 when the county purchased the land for a park. Not long after the purchase, state environmental officials put the land on the state Superfund list and ordered expensive cleanups.

After years of studies and legal action to track down the successors of the old mining firms, the county finished cleanup work in the late 1990s. Crews dug out old rocks known as calcines that had been heated in furnaces. They stored them in a remote ravine and filled in the areas with up to 5 feet of clean dirt.

The state Department of Toxic Substances Control removed the park from the Superfund list in 2000 and still conducts annual tests of the site.

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