The Animas Mountains lie near the Chihuahuan Desert, the Sonoran Desert, the Sierra Madre Occidental of Mexico, and the mountains surrounding the headwaters of the Gila River. Biotic influences from these regions, as well as the more distant Rocky Mountains, give the southern portion of the range a great diversity of species, including approximately 130 species of birds, 60 species of mammals, and 40 species of reptiles.