New Almaden Quicksilver Mine - inland mercury deposit

The New Almaden Quicksilver Mining District in San Jose was the first and most productive mercury (quicksilver) mining district in the United States, producing cinnabar and elemental mercury from the mid-1800s through the 20th century. The mercury deposits are a geologic anomaly for the Santa Clara Valley, hosted in silica-carbonate veins in the local rock and concentrated enough to support large-scale mining. Historic mining and tailings from the district have contributed to ongoing mercury contamination issues in the Guadalupe River watershed and associated fisheries advisories. The site is now part of Almaden Quicksilver County Park and includes preserved mining-era structures and landscapes.