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
Rangipo Desert factors lowering the temperature below zero for days on end. Much of the desert lies at an altitude of over , and a considerable proportion of it is over above sea level. Due to the unproductive nature of the land and the extreme winter climate, the region is largely uninhabited. The town of Waiouru, with its army camp, lies to the south and much of the southern part of the desert is used for training purposes. To the north of the desert lies the Rangipo prison farm. Many of the North Island's largest rivers have their headwaters in the area,