Sonoran Desert - geography.

Sonoran Desert - geography. Sonoran Desert, large, low, arid region lying primarily in southwestern Arizona, southeastern California, and northwestern Mexico (some definitions also include most of Mexico's Baja California Peninsula). The desert is bounded by the Mojave Desert on the north, the Arizona highlands region on the east, Mexico's Sierra Madre Occidental on the south (see Sierra Madre), and the Gulf of California and the Pacific Ocean on the west. The Sonoran covers about 310,799 sq km (about 120,000 sq mi). The desert probably takes its name from the Tohono O'Odham (Papago) language term Sonota, which means "place of plants." While the Sonoran Desert accounts for only 20 percent of Arizona's land area, more than 80 percent of the state's population lives here, mainly in the rapidly growing areas of Phoenix and Tucson. Other cities within the region include Indio, Blythe, and El Centro in California; Yuma in Arizona; and Hermosillo, Guaymas, and Ciudad Obregón in Mexico. The desert supports numerous Native American reservations and United States military bases and air force and gunnery ranges. Large portions of the desert are preserved as parkland; Joshua Tree National Park, Saguaro National Park, Organ Pipe Cactus National Monument, Cabeza Prieta National Wildlife Refuge, Imperial National Wildlife Refuge, and Kofa National Wildlife Refuge are all located in the Sonoran. Elevations in the Sonoran Desert are generally low when compared with the surrounding regions, averaging only about 300 m (about 1,000 ft). The most prominent mountain ranges within the desert are California's Chocolate and Chuckwalla mountains, Arizona's Kofa and Harquahala mountains, and Mexico's Cerro del Pinacate. Daily summer temperatures in the Sonoran Desert, one of the driest and hottest regions in North America, exceed 38° C (100° F). Winters are predictably warm; mean January temperatures range from 10° to 16° C (50° to 60° F). Most parts of the desert receive less than 250 mm (10 in) of rainfall a year. Thus, most of the region's water is taken from the ground or diverted from several rivers: the Colorado River, the Gila River, the Salt River, the Yaqui River, the Fuerte River, and the Sinaloa River, all of which run into and through the desert from the surrounding highlands. Irrigated agriculture is a crucial part of the Sonoran Desert's economy, and ground water levels have dropped drastically since the 1960s. A huge supplementary water system, the Central Arizona Project, brings millions of liters of water each day from the Colorado River to the east side of the Sonoran Desert, particularly the Phoenix and Tucson areas. The desert possesses unique vegetation with well-developed abilities to grow in infertile soil, to gather and conserve moisture, and to withstand great daytime heat as well as cold nights and abrasive winds. The most conspicuous flora are cacti, including the saguaro, prickly pear, cholla, staghorn, organ-pipe, and barrel cactus varieties. Additional indigenous plants include the creosote bush, burro bush, mesquite, palo verde, Joshua tree, and ironwood. Two introduced plants--buffel grass and the tamarisk, or salt cedar, bush--have seriously disturbed the ecological balance among native species. The region's reptilian wildlife includes the desert tortoise, Gila monster, chuckwalla, banded gecko, Colorado desert fringe-toed lizard, desert horned lizard, and numerous species of rattlesnake. Mammals include pocket gophers, mice, pack rats, kangaroo rats, squirrels, rabbits, foxes, coati, coyotes, bobcats, peccaries, mule deer, mountain lions, and bighorn sheep. Birds include cactus wren, elf owl, Arizona crested flycatcher, Gambel's quail, Gila woodpecker, and white-winged dove. The region possibly was inhabited as early as 10,000 years ago. By AD800 the Hohokam people had created a sophisticated culture in a wide region encompassing present-day Phoenix. They had permanent villages and a complex canal system to irrigate their crops. This civilization was eventually replaced by other Native American groups. When the first Spaniards entered the desert in the middle of the 15th century, they encountered the Yaqui, Yuma, Tohono O'Odham (Papago), Akimel O'Odham (Pima), and other peoples. The Spaniards colonized much of the lower desert. After 1848 gold seekers traveling to California created an important route, the Gila Trail, which ran east to west and along the Gila River across the desert from Tucson to Los Angeles. By 1881 the Southern Pacific Railroad, following the same general course, had been completed; today Interstate 8 mostly follows this route through the desert. In recent years the highly urbanized areas of Tucson and Phoenix have increasingly sprawled across the desert, prompting fears that the natural beauty of the desert is being destroyed. Contributed By: James W. Byrkit Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.