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
Western Desert (Egypt) Nile valley. To the south, beyond the Bahariya oasis lies the Black Desert, an area of black volcanic hills and dolerite deposits. Beyond this, north of Farafra, lies the White Desert, an area of wind-sculpted chalk rock formations, which give the area its name. To the south of Kharga the plateau rises towards the Gilf Kebir, an upland region lying astride the Egypt-Sudan border and home to pre-historic sites such as the Cave of Swimmers. In the south-west, near the point where the borders of Libya, Sudan and Egypt meet, is an area of desert glass, thought to have been