Wheeler Geologic Area is an unusual volcanic landscape in the San Juan Mountains of southern Colorado, where highly eroded ash from eruptions of the La Garita Caldera about 25 million years ago has been worn into pale, jagged spires, gullies, and broken walls near the crest of the range. Named for Captain George M. Wheeler, who surveyed the region for the U.S. Army in 1874, the site became Colorado’s first national monument in 1908 under President Theodore Roosevelt. Because its remoteness limited visitation, the monument was abolished in 1950 under President Harry Truman, and the area was placed within Rio Grande National Forest. It is now part of the La Garita Wilderness.