Desert bighorn sheep establish two desert areas in southwestern Arizona to help preserve the desert bighorn sheep: Cabeza Prieta National Wildlife Refuge and the Kofa National Wildlife Refuge. In 1941, the San Andres National Wildlife Refuge in New Mexico was added. Desert bighorn sheep populations have trended upward since the 1960s when their population was estimated at 6,700-8,100. The upward trend was caused by conservation measures, including habitat preservation. In 1980, desert bighorn sheep populations were estimated at 8,415-9,040. A state-by-state survey was conducted a few years later and estimated the overall US desert bighorn sheep population at 15,980. The 1993 estimate of
Painted Desert (Arizona) desert is composed of stratified layers of easily erodible siltstone, mudstone, and shale of the Triassic Chinle Formation. These fine grained rock layers contain abundant iron and manganese compounds which provide the pigments for the various colors of the region. Thin resistant lacustrine limestone layers and volcanic flows cap the mesas. Numerous layers of silicic volcanic ash occur in the Chinle and provide the silica for the petrified logs of the area. The erosion of these layers has resulted in the formation of the badlands topography of the region. In the southern portions of the desert the remains of a