The mountainous areas of the triangle from New Mexico to California to South Dakota contained hundreds of hard rock mining sites, where prospectors discovered gold, silver, copper and other minerals (as well as some soft-rock coal). Temporary mining camps sprang up overnight; most became ghost towns when the ores were depleted. Prospectors spread out and hunted for gold and silver along the Rockies and in the southwest. Soon gold was discovered in Colorado, Utah, Arizona, New Mexico, Idaho, Montana, and South Dakota (by 1864).