[4] Cinnabar, a bright red mercury ore, was used by the Ohlone people for paint, but the settlers soon saw its potential to produce quicksilver.

On appeal to the Supreme Court of the United States the claim was found invalid in a decision rendered March 10, 1863.

Mindful of the possibility of losing the loyalty of California during the Civil War, the federal government backed off[19] and Barron, Forbes Company was allowed to sell it to American investors for $1.75 million.

[20][21] Arthur De Wint Foote worked at New Almaden in the late 1870s under James Butterworth Randol.

Her illustrated correspondence about New Almaden, "A California Mining Camp", appeared in the February 1878 issue of Scribner's Monthly.

[23] 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.

Mining operations resulted in mercury pollution of the Guadalupe River and South San Francisco Bay, impacting birds and aquatic species.

In 2005 the responsible parties, which include private companies and local government agencies, agreed to a legal settlement of approximately US$6,750,822 for restoration projects.

[28] By the time Santa Clara County bought the mines in 1976 and ended operations, 1,137,727 flasks totaling 83,974,076 pounds (38,090 metric tons) of mercury (worth more than US$70 million) had been extracted.

During the coldest storms of the winter season, it is not uncommon for the high summits to receive a light dusting of snow (which usually melts by noon).