Silverton, Colorado in the context of "National Historic Landmark District"

The San Juan Mountains is a high and rugged mountain range in the Rocky Mountains in southwestern Colorado and northwestern New Mexico. The area is highly mineralized (the Colorado Mineral Belt) and figured in the gold and silver mining industry of early Colorado. Major towns, all old mining camps, include Creede, Lake City, Silverton, Ouray, and Telluride. Large scale mining has ended in the region, although independent prospectors still work claims throughout the range. The last large-scale mines were the Sunnyside Mine near Silverton, which operated until late in the 20th century, and the Idarado Mine on Red Mountain Pass, which closed in the 1970s. Famous old San Juan mines include the Camp Bird and Smuggler Union mines, both located between Telluride and Ouray.

The Summitville mine was the scene of a major environmental disaster in the 1990s when the liner of a cyanide-laced tailing pond began leaking heavily. Summitville is in the Summitville caldera, one of many extinct volcanoes making up the San Juan volcanic field. One, La Garita Caldera, is 35 miles (56 km) in diameter. Large beds of lava, some extending under the floor of the San Luis Valley, are characteristic of the eastern slope of the San Juans. The eruption of the La Garita Caldera shaped the San Juan Mountains by completely obliterating the volcanoes that once stood in the area.

37°54′54.40″N 107°42′1.1″W / 37.9151111°N 107.700306°W / 37.9151111; -107.700306

The Idarado Mine was a mining operation in the San Juan Mountains of Ouray County, Colorado near the now-ghost town of Guston, producing primarily lead, zinc and silver along with small amounts of gold and copper. The mine is within the Sneffels-Red Mountain-Telluride mining district. The remains of the operation are visible from the Million Dollar Highway, north of Red Mountain Pass, between Ouray and Silverton, Colorado. The tunnels of the Idarado extend some 5 miles (8 km) west under 13,000 foot (4,000 m) mountains to the Pandora Mill near Telluride, a trip of more than 60 miles (100 km) by highway.