Colorado's ghost towns are mostly mining camps. Gold and silver strikes from the 1860s through the 1890s put camps high in the Front Range, the Sawatch and Elk ranges and the San Juan Mountains, and many emptied when the mines closed, often after silver lost its value in 1893. Coal camps in Las Animas and Huerfano counties, railroad and stage stops, and farm towns on the eastern plains make up most of the rest. Wikipedia's list puts the state's total above 1,500 ghost towns, with visible remains at only about 640.
In our index, Park, Gunnison and Chaffee counties have the most sites. What survives depends on altitude, ownership and care. Animas Forks at 11,185 feet and Independence at about 10,900 feet still have cabins because the Bureau of Land Management and the Aspen Historical Society stabilized them. Saint Elmo kept its main street and a few residents. Other towns are gone: Kokomo lies under mine waste, and nothing is left of the uranium company town of Uravan. Some townsites are private land even inside a national forest, as part of Independence is.