"Indians living near the old Santa Clara Mission, about fifty miles from the present city of San Francisco... used to apply red and yellow pigments from the "Cave of the Red Earth" near there for personal adornment. In 1845 Captain Andres Castillero of the [, who had studied chemistry and metallurgy at the College of Mines in Mexico City, discovered near the Santa Clara Mission an in which he easily detected metallic mercury. When Don Manuel Herrera of that College of Mines analyzed specimens of this ore he found an average mercury content of 35.5 per cent and reported that some pieces were practically pure ."