Rio Grande National Forest is a 1.86 million-acre (7,530 km²) ^[1] 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.^[1] 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 Monte Vista, Colorado, but plan to move to Del Norte.^[2] There are local ranger district offices in Del Norte, La Jara, and Saguache.^[3]

There are four officially designated wilderness areas lying within Rio Grande National Forest that are part of the National Wilderness Preservation System. All of them extend partially into neighboring National Forests, and one of these also onto National Park Service land (as indicated).

• La Garita Wilderness (mostly in Gunnison NF)
• Sangre de Cristo Wilderness (the largest part in San Isabel NF; also partly in Great Sand Dunes National Park and Preserve)
• South San Juan Wilderness (partly in San Juan NF)
• Weminuche Wilderness (mostly in San Juan NF)

According to the Köppen Climate Classification system, Rio Grande Reservoir has a warm-summer humid continental climate, abbreviated "Dfb" on climate maps. The hottest temperature recorded at Rio Grande Reservoir was 89 °F (31.7 °C) on July 6, 1989 and July 14, 2003, while the coldest temperature recorded was −46 °F (−43.3 °C) on December 8, 1978.^[4]

• List of largest National Forests
• List of U.S. National Forests