In most modern classifications, the deserts of the United States and northern Mexico are grouped into four distinct categories. These distinctions are made on the basis of floristic composition and distribution — the species of plants growing in a particular desert region. Plant communities, in turn, are determined by the geologic history of a region, the soil and mineral conditions, the elevation and the patterns of precipitation.
Three of these deserts — the Chihuahuan, the Sonoran and the Mojave — are called “hot deserts,” because of their high temperatures during the long summer and because the evolutionary affinities of their plant life are largely with the subtropical plant communities to the south. The Great Basin Desert is called a “cold desert” because it is generally cooler and its dominant plant life is not subtropical in origin.
Chihuahuan Desert: A small area of southeastern New Mexico and extreme western Texas, extending south into a vast area of Mexico.
Great Basin Desert: The northern three-quarters of Nevada, western and southern Utah, to the southern third of Idaho and the southeastern corner of Oregon. According to some, it also includes small portions of western Colorado and southwestern Wyoming. Bordered on the south by the Mojave and Sonoran Deserts.
Mojave Desert: A portion of southern Nevada, extreme southwestern Utah and of eastern California, north of the Sonoran Desert.
Sonoran Desert: An arid region covering approximately 100,000 square miles in southwestern Arizona and southeastern California, as well as most of Baja California and the western half of the state of Sonora, Mexico. Subdivisions of this hot, dry region include the Colorado and Yuma deserts.
This classification of North American deserts is by no means universally accepted by all biologists, geologists and other scientists. For instance, some maintain that the Mojave is not a distinct desert at all, but simply a transition zone between the Great Basin and Sonoran deserts. Even among those who agree upon this classification, there is disagreement over the exact geographic areas circumscribed by each of the four deserts. Some scientists would use animals and other criteria, as well as distribution of plant species, to determine desert different boundaries for these four deserts.
The Colorado Plateau is another major source of disagreement among scientists. This semiarid region of southern Utah and northern Arizona contains many majestic national parks, including Arches and Grand Canyon. Yet, experts cannot agree on the desert classification of this geologically distinct region. Some do not include the Colorado Plateau within any desert at all; others call this area the Painted Desert; still others consider this region the southeastern extent of the Great Basin Desert.