The Ohlone used the red ore cinnabar from these hills for paint. In 1845 a Mexican cavalry captain, Andrés Castillero, recognized it as a source of mercury, or quicksilver, and mining began in 1847, just in time for the Gold Rush, when mercury was used to separate gold from ore. The mines were named after Almadén in Spain, a mercury mine since Roman times; the name comes from the Arabic for “the mine.” In 1863 federal agents sent to seize the mine were turned back at the gates by armed miners.
By the time Santa Clara County bought the mines in 1976, about 84 million pounds of mercury had been taken out. The land is now Almaden Quicksilver County Park, about 4,163 acres of trails past old mine buildings such as English Camp, built by Cornish miners in the 1860s. The Casa Grande in the historic village holds a mining museum. The local paper’s name, the Mercury News, is traced to the mines.