Gold from the Eureka Mine sustained Pete Aguereberry for 40 years. Historians estimate that Aguereberry extracted about $175,000 worth of gold, then valued at $20 per ounce, from Providence Ridge during his lifetime. On the hillside is the Cashier Mill, built in 1909. Powered by gasoline engines, the mill pulverized the ore, then chemical processes using mercury and cyanide extracted the gold. The mill site and surrounding mines were originally part of Shorty Harris's claim, which he sold to the Cashier Mining Company. Aguereberry later bought the mill site, adding to the seven Death Valley mining claims he already owned. Gold prospectors like Aguereberry looked for veins of quartz or seams of red or yellow iron-stained rock. Miners followed the veins, drilling and blasting to break the ore loose, then sent the ore to mills to extract the gold. A profitable mine would yield about an ounce of gold per ton of ore. In recent years, the Eureka Mine has become a winter home for the endangered Townsend big-eared bat, and activity in the mine during winter months can awaken the bats, causing distress and even death.