Wehausen (1988 and 1998) listed additional areas that were probably used. These areas constituted approximately 13 populations that currently lack reproducing populations (i.e., use by females). Although there is no way to know precisely what the historic population size was in the Sierra Nevada, the leading expert on these animals has estimated that there were probably at least 1,000 bighorn in the Sierra Nevada prior to 1850 (Wehausen, pers. comm.).

Shortly after the immigration of Europeans to the Sierra Nevada in the mid-1800s, bighorn population began to decline. Wehausen et al. (1987) investigated patterns of population losses for bighorn sheep populations in California and found that these losses were not a phenomenon of just the distant past, but have continued through the twentieth century. This pattern also holds for the Sierra Nevada. Including the extreme southern populations, there is evidence suggesting that 10 populations made it to the twentieth century. At mid-century, Jones (1950) documented the existence of three populations and postulated two more based on signs and reported sightings, while a quarter century later only two populations remained (Wehausen 1980).

Recent causes of population declines are understood, but specific causes of population losses prior to 1970 are unknown, with one possible exception. In the 1870s, a large die-off of bighorn sheep was documented west of the Kern River and attributed to loss of fur due to scabies, presumably contracted from domestic sheep (Jones 1950). Market hunting for mining towns may have played a role in some locations, but die-offs from pneumonia contracted from domestic sheep were probably the most significant cause of losses (SNBSIAG 1997).Large numbers of domestic sheep were grazed seasonally over much of the Sierra Nevada prior to the turn of the century, and this practice continued well into this century along the eastern scarp (Wehausen 1988). It is now well documented that, as part of their normal respiratory tract, domestic sheep carry flora, bacterial strains that are fatal to bighorn sheep (Onderka and Wishart 1988; Foreyt 1989; Callan et al. 1991).

Almost all the habitat of existing and extinct bighorn sheep populations in the Sierra Nevada is currently in public ownership and the majority of it is administered by the U.S. Forest Service. Currently, Sierra bighorn exist in five populations: the Mount Williamson and Mount Baxter populations, which are composed of native sheep, and the Lee Vining Canyon, Wheeler Ridge, and Mount Langley populations, which are descended from sheep taken from the Mount Baxter population and reintroduced to historic habitat. All these populations live substantially within Inyo National Forest and the Forest Service has acknowledged the public "demand" for these sheep for recreational and scientific purposes, as well as opined that, "[i]f all identified suitable habitat on the Forest were occupied, it could support as many as one thousand animals." (Inyo National Forest1988 at 63).

The National Park Service manages the alpine ranges west of the crest of the Sierra Nevada of four of the five populations (excepting Wheeler Ridge), involving Sequoia Kings Canyon, and Yosemite National Parks. A small amount of escarpment base winter range falls on land administered by the U.S. Bureau of Land Management (Bleich et al. 1991). Finally, a small amount of private land in the form of patented mining claims exists within existing historic bighorn habitat (USDA 1983).