• Southwestern deserts belong to four distinct groupings.desert image by Carol Tomalty from Fotolia.com
  
  Southwestern United States deserts belong to four categories developing from factors of altitude, rainfall and mineral composition of the soil that influence types of plants each produces. High temperatures during lengthy summers make the Chihuahuan, Sonoran and Mojave Deserts bear subtropical plants while the cooler Great Basin Desert produces dominant non-subtropical flora. Two of the deserts reach across an international border while warm winters in another of the four provide tourist destinations in two southwestern states.
  
  

Chihuahuan Desert

• Covering more than 200,000 square miles, areas of the Chihuahuan Desert border U.S. Route 191 of western Arizona, run along interstate 40 in the north, edge east into New Mexico and farther to Texas' U.S. Route 385 while extending south across the international border into Mexico. It is the largest desert in North America. The yearly rainfall reaches less than 10 inches during the summer.
  
  

Great Basin Desert

• Expanding to nearly 190,000 square miles, the Great Basin Desert is America's largest. Bound by the Sierra (saw toothed) Nevada Mountain Range on its western edge, the Great Basin Desert edges inside the Rocky Mountains to the east, while the Columbian Plateau rims the northern edges of this vast arid region. To the south, the Mojave and Sonoran Deserts make this higher elevated northern desert cooler, with altitudes from 4,000 to 6,500 feet. The Great Basin annual rainfall averages between 7 and 12 inches, with winter providing snowfall.
  
  

Sonoran Desert

• Including southwestern Arizona, southeastern California into international territory of most of Baja California and the western half of the Mexican state of Sonora, the Sonoran Desert covers120,000 square miles and is the hottest in North America. Winter storms from the Pacific and yearly summer monsoons create diverse plant life, including the famous and protected Saguaro cactus. Warm winters in this arid region attract tourists to resorts in Palm Springs, California and Tucson and Phoenix, Arizona.
  
  

Mojave Desert

• Known as a rain shadow desert created by upwind high-elevated mountains preventing moisture from reaching its boundaries, the 25,000 square mile Mojave Desert covers parts of southern Nevada, southwestern Utah, eastern California and portions of western Arizona. Located between 34 and 38 degree north latitudes, with elevations typically ranging from 3,000 to 6,000 feet, the Mojave Desert also includes the lowest point in North America. California's Death Valley National Park is 282 feet below sea level.