The first house was built in August 1877 after two prospectors working in the area of the future Opportunity Mine, collected loose pieces of rock (float is the geologic term) assayed at $160 per ton in gold and silver. Soon, ore was discovered at the nearby Rattlesnake vein (geology) and a placer deposit of gold was found in November at the Rattlesnake and Wicks gulches. Ore was pulverized with arrastres located in Hillsboro, including a 10-stamp mill built in 1878. Total production prior to 1904 was about $6,750,000. Between 1911 and 1931, total production of gold, silver and copper was about $150,000. In his report, Harley wrote, "The ore deposits of the Hillsboro or Las Animas mining district are of four general types as follows: (1) fissure veins in andesite flows, (2) disseminated deposits in monzoniteporphyry, (3) replacement deposits in limestone, and (4) placer gold deposits."