support a variety of wildlife species, including 51 species of native mammals, 307 species of birds, 36 species of reptiles, 3 species of amphibians, and 2 species of native fish. Small mammals are more numerous than large mammals, such as bighorn sheep, coyotes, bobcats, kit foxes, cougars, and mule deer. Mule deer are present in the pinyon/juniper associations of the Grapevine, Cottonwood, and Panamint ranges. Bighorn sheep are a rare species of mountain-dwelling sheep that exist in isolated bands in the Sierra and in Death Valley. These are highly adaptable animals and can eat almost any plant. They have no known predators, but humans and burros compete for habitat. The ancestors of the Death Valley pupfish swam to the area from the Colorado River via a long-since dried-up system of rivers and lakes (see Lake Manly). They now live in two separate populations: one in Salt Creek and another in Cottonball Marsh. Death Valley is one of the hottest and driest places in North America, yet it is home to over 1,000 species of plants; 23 of which, including the very rare rock lady (Holmgrenanthe), are not found anywhere else. Adaptation to the dry environment is key. For example, creosote bush and mesquite have tap-root systems that can extend down in order to take advantage of a year-round supply of ground water. The diversity of Death Valley's plant communities results partly from the region's location in a transition zone between the Mojave Desert, the Great Basin Desert and the Sonoran Desert. This location, combined with the great relief found within the park, supports vegetation typical of three biotic life zones: the lower Sonoran, the Canadian, and the arctic/alpine in portions of the Panamint Range. Based on the Munz and Keck (1968) classifications, seven plant communities can be categorized within these life zones, each characterized by dominant vegetation and representative of three vegetation types: scrub, desert woodland, and coniferous forest. Microhabitats further subdivide some communities into zones, especially on the valley floor. Unlike more typical locations across the Mojave Desert, many of the water-dependent Death Valley habitats possess a diversity of plant and animal species that are not found anywhere else in the world. The existence of these species is due largely to a unique geologic history and the process of evolution that has progressed in habitats that have been isolated from one another since the Pleistocene epoch. Activities Sightseeing is