The New Almaden Quicksilver Mine in Santa Clara County, California, is the oldest and most productive quicksilver (i.e., mercury) mine in the United States. The site was known to the Ohlone Indians for its cinnabar long before a Mexican settler discovered the ores in 1820. By the time they were identified as mercury, the mine was perfectly timed to supply the California Gold Rush. The mine ran intermittently after 1927 and eventually closed. It was purchased by the county and is now part of Almaden Quicksilver County Park.
The Spanish mine had operated at least since Roman times. The term Almaden, is derived from Arabic (through the medieval islamic occupation of Spain), meaning "the mine".
Arthur De Wint Foote worked at New Almaden in the late 1870s under Randol.
The entrances to the mines are closed off. After being identified as a superfund site and subsequent containment activities, the mining area can now be visited as part of the Santa Clara County Almaden Quicksilver county park.
Historical life at the New Almaden mine was vividly drawn by Mary Hallock Foote, the wife of Arthur DeWint Foote, the Resident Engineer from 1876. Her illustrated correspondence about New Almaden, "A California Mining Camp", appeared in the February 1878 issue of Scribner's Monthly. New Almaden also features prominently in her memoir A Victorian Gentlewoman in the Far West, which was later fictionalized by Wallace Stegner in his novel Angle of Repose.
It was declared a National Historic Landmark in 1961.
The New Almaden Quicksilver Mining Museum is located in the Casa Grande (big house) at 21350 Almaden Road in New Almaden. La Case Grande, an 1854 revival-style mansion designed and built by architect Francis Meyers, was the official residence and office of the mine superintendents, as well as a country retreat for wealthy mine investors. The mansion now serves as the site of the New Almaden Quicksilver Mining Museum, which contains exhibits about the history of mercury mining and the cultural history of the mining communities at New Almaden. The exhibits include a mine diorama of the interior of a mine shaft, mining equipment and techology, a mine manager's office with period displays, and artifacts from Cornish, Mexican and Chinese mining families.