San Luis Valley in the context of "Continental Divide"

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.

Rio Grande National Forest is a 1.86 million-acre (7,530 km) U.S. national forest located in southwestern Colorado. The forest encompasses the San Luis Valley, which is the world's largest agricultural alpine valley, as well as one of the world's largest high deserts located around mountains. The Rio Grande rises in the forest, and the Continental Divide runs along most of its western border. The forest lies in parts of nine counties. In descending order of land area within the forest they are Saguache, Mineral, Conejos, Rio Grande, Hinsdale, San Juan, Alamosa, Archuleta, and Custer counties. Forest headquarters are currently located in Del Norte, Colorado. There are local ranger district offices in Del Norte, La Jara, and Saguache.

The Western Slope is a colloquial term generally understood to describe the part of the state of Colorado west of the Continental Divide. Bodies of water west of the Divide flow toward the Pacific Ocean; water that falls and flows east of the Divide heads east toward the Gulf of Mexico. The Western Slope encompasses about 33% of the state, but has just 10% of the state's residents. The eastern part of the state, including the San Luis Valley and the Front Range, is the more populous portion of the state.