Keystone-Union Mine (Calaveras Copper), Copperopolis
Keystone-Union Mine (Calaveras Copper), Copperopolis Mines (Copperopolis group), Copperopolis, Foothill Copper Belt, Calaveras Co., California, USA : A former Cu-Ag-Au-Pb mine located in the NE¼SW¼ sec. 34, T2N, R12E, MDM, in the town of Copperopolis, on private (patented) land. Operated during the period 1861 to 1946. MRDS database stated