Founded in 1853 from a consolidation of two or more small claims. It reached a depth of 2,680 feet and produced about $24 million in gold.

Keystone’s early years were plagued with production and ownership problems; luckily, a rich new vein was discovered in 1866, enabling the mine to yield a monthly gold production average of $40,000, making the Keystone one of the most lucrative California mines. The Keystone mine was closed in 1942 when the government closed all operations that did not pertain to the war effort.