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
Mu Us Sandyland name—for example, a map in Julia Lovell's book "The Great Wall: China Against the World 1000 BC–2000 AD" shows the Ordos Desert only in the portion of Inner Mongolia, which lies south of the Yellow River. Several research papers cited below claim that the Mu Us Sandy Land includes part of Shaanxi and Gansu. A clear delineation of the area is still needed here, based on multiple sources. The Mu Us Sandy Land of north central China lies at 37°30'–39°20'N,107°20'–111°30'E and covers 40,000 km. As part of the Ordos Plateau, the elevation ranges from 1,000m to 1,300m (as low as