The desert rosy boa is found in the Aridoamerica ecoregion, in the southwestern United States in the states of California and Arizona, and northwestern Mexico in the states of Baja California and Sonora. In California, the species inhabits extreme southern San Diego County, California within the Tijuana River and Otay watersheds. In Arizona, the desert rosy boa occupies the western areas of the Sonoran Desert. In Sonora, the desert rosy boa ranges from the border with the United States south throughout the Sonoran Desert to at least as far south as Ortiz. In Baja California, the desert rosy boa is almost ubiquitous ranging throughout the entire peninsula except in areas of extremely dry or rockless desert. Behavior The desert rosy boa spends most of its life concealed beneath rocks and in crevices to escape the elements and natural predators. Granite outcroppings are the most common geologic association inhabited by the desert rosy boa. Less often, it is found in association with volcanic or other rock types. Only in rare places does the desert rosy boa inhabit rockless environments. In areas with few rocks, the desert rosy boa uses rodent burrows for concealment. The desert rosy boa's activity season follows local weather patterns; however, it is generally dormant during the winter, and active during the spring, summer, and fall. Like all snakes, it is dependent on external temperatures to promote such normal bodily functions as digestion and gestation. Throughout most of its range, the winter is too cold for these functions and the desert rosy boa goes into a dormant state called brumation. The spring is breeding season, resulting in its highest rate of activity. Most specimens of the desert rosy boa are encountered in spring as they leave the security of their rock piles and crevices to seek mates. Another reason why the desert rosy boa may be active on the surface of the ground is to find prey or new territory. The surface activity of the desert rosy boa can take place during any hour of the day, but during hot weather, it is primarily nocturnal. In the spring, it is often out in the afternoon and early evening. In the late spring and summer, this activity period switches from dusk to late into the night. Because most populations of the desert rosy boa live in exceedingly dry habitats, activity is often highly moisture-dependent. During dry periods it remains