The desert tortoise is a widespread species of the southwestern United States and Mexico, well adapted to living in the often harsh desert environment. Adult desert tortoises range in size from 9.25 to 14.5 inches while hatchlings are about the size of a silver dollar. The average home range of a tortoise is from approximately 27 to 131 acres. Historically, the desert tortoise was distributed widely throughout the Mojave, Colorado and Sonoran deserts of southeastern California, southern Nevada, southwestern Utah and western Arizona.
Current distribution is considerably more patchy within the historic range.
In 1990, the Fish and Wildlife Service listed the desert tortoise as threatened in the northern and western parts of its geographic range due to declines in its population density as well as the increasing loss of desert habitat from urban development and recreation. The FWS estimates that some local populations in California, Nevada and Arizona may be decreasing by as much as 20 percent per year. The causes of the tortoise's population declines differ somewhat within and between population segments, but are primarily related to human activities such as urban development, illegal collecting, vandalism, shell disease, predation by common ravens, crushing by vehicles both on and off roads and trampling by livestock. While loss and degradation of habitat is a leading threat to the continued existence of the tortoise, of particular concern is the recent appearance of a highly infectious and usually fatal upper respiratory tract disease, which was apparently introduced through the release of captive tortoises. The outbreak of this disease has caused the death of thousands of wild tortoises in the Mojave desert during the last few years.