The sky islands also supply the surrounding desert foothills with flowing water during the spring runoff and after the summer storms of the New Mexican monsoon season.

Six of the top ten major population centers of the region are found within its borders: Phoenix, Tucson, Mesa, Chandler, Glendale, and Scottsdale, all in Arizona.

[36] Maize began to be cultivated in the region sometime during the early first millennium BC, but it took several hundred years for the native cultures to be dependent on it as a food source.

The area once occupied by the ancestral Puebloans became inhabited by several American Indian tribes, the most populous of which were the Navajo, Ute, Southern Paiute, and Hopi.

Their village of Oraibi, settled in approximately AD 1100, is, along with Acoma Sky City in New Mexico, one of the oldest continuously occupied settlements in the United States.

[71][72] In 1776, two Franciscan priests, Francisco Atanasio Domínguez and Silvestre Vélez de Escalante, led an expedition from Santa Fe heading to California.

In 1821 Mexico achieved its independence from Spain and shortly after, in 1824, developed its constitution, which established the Alta California territory, which was the same geographic area as the earlier Spanish province.

[80] Initially, its borders included parts of what would become several other states: almost half of New Mexico, a third of Colorado, and small portions of Kansas, Oklahoma, and Wyoming.

[85] The New Mexico Territory was expanded along its southern extent, to its current border, with the signing of the Gadsden Purchase Treaty on December 30, 1853,[71][86] which was ratified by the U.S. Congress, with some slight alterations, in April 1854.

Initially, only the western 2/3 of what is currently the State of Nevada was included in the territory, with its boundary to the east being the 39th meridian west from Washington, and to the south the 37th parallel.

Colonel John Robert Baylor forced the surrender of the small Union garrison stationed at Fort Fillmore, near Mesilla, New Mexico.

[108] In 1901, the Santa Fe Railroad reached the South Rim of the Grand Canyon, opening the way for a tourism boom,[109] a trend led by restaurant and hotel entrepreneur Fred Harvey.

These military installations form a kind of hinterland around the El Paso-Tucson region, and are served by scientific and residential communities such as Sierra Vista, Las Cruces, and Alamogordo.

[120] The fourth subregion Meinig calls the "Northern Corridor and Navajolands," a major highway and railway trunk which connects Albuquerque and Flagstaff.

In the early years of the United States, newly colonized lands lying immediately west of the Appalachian Mountains were detached from North Carolina and given the name Southwest Territory.

However, as territories and eventual states to the west were added after the Mexican–American War, the geographical "Southwest" expanded, and the relationship of these new acquisitions to the South itself became "increasingly unclear.

This is an area containing the basic elements of Southern history, culture, politics, religion, and linguistic and settlement patterns, yet blended with traits of the frontier West.

One of these distinguishing characteristics in Texas—in addition to having been a Confederate state during the Civil War—is that Indigenous and Spanish American culture never played a central role in the development of this area in relative comparison to the others, as the vast majority of settlers were Anglo and blacks from the South.

[127] The fact that a majority of residents of Texas and Oklahoma—unlike those in other "southwestern" states—self-identify as living in the South and consider themselves southerners rather than the West and westerners—also lends to treating these two states as a somewhat distinct and separate entity in terms of regional classification.

[131] Birds of prey include the red-tailed hawk (Buteo jamaicensis), Cooper's hawk (Accipiter cooperii), the osprey (Pandion haliaetus), golden eagles (Aquila chrysaetos), Harris's hawk (Parabuteo unicinctus),[132] American kestrel (Falco sparverius), peregrine falcon (Falco peregrinus),[133] the gray hawk (Buteo plagiatus),[134] the American barn owl (Tyto furcata), the western screech owl (Megascops kennicottii), the great horned owl (Bubo virginianus), the elf owl (Micrathene whitneyi), and the burrowing owl (Athene cunicularia)[135] Other bird species include the turkey vulture (Cathartes aura), the black vulture (Coragyps atratus),[136] the northern cardinal (Cardinalis cardinalis), the blue grosbeak (Passerina caerulea),[137] the house finch (Haemorhous mexicanus), the lesser goldfinch (Spinus psaltria),[138] the broad-billed hummingbird (Cynanthus latirostris), the black-chinned hummingbird (Archilochus alexandri), Costa's hummingbird (Calypte costae),[139] Gambel's quail (Callipepla gambelii),[140] the common raven (Corvus corax),[141] the Gila woodpecker (Melanerpes uropygialis), the gilded flicker (Colaptes chrysoides),[142] the cactus wren (Campylorhynchus brunneicapillus), the rock wren (Salpinctes obsoletus),[143] and the federally endangered Southwest willow flycatcher (Empidonax traillii extimus).

[145] Mammal species include the bobcat, coyote, black bear, black-tailed jackrabbit, desert cottontail, desert bighorn sheep, mule deer, white-tailed deer, gray fox, mountain lion, river otter, long-tailed weasel, western spotted skunk, pronghorn, raccoon, cactus mouse, and Ord's kangaroo rat, all of which can be found in parts of every southwestern state.

Fish and Wildlife Service study reported a minimum population of 241 Mexican wolves in southwest New Mexico and southeast Arizona at the beginning of 2023.

Lizards are highly represented in the region, the most distinctive denizen being the Gila monster, native only to the American Southwest and the state of Sonora in Mexico.

[153][154] Desert pupfishes are several closely related species of fish in the genus Cyprinodon, many of which are found in isolated spring-fed ponds hundreds of miles from each other, ranging from far West Texas to Death Valley in California.

The metropolitan areas of Phoenix, Tucson, Las Vegas, and El Paso hardly ever receive any snow at all, as they are strictly desert lands with mountains.

The High Desert also receives a decent amount of snowfall in the winter (with the exception of California, southern Nevada and southwestern Utah) but melts very quickly.

[157] The Southwest also experiences multi-year and multi-decade episodes of severe drought, including the ongoing southwestern North American megadrought which emerged starting year 2000.

Hispanic Americans can be found in large numbers in every major city in the Southwest such as El Paso (80%), San Antonio (63%), Los Angeles (48%), Albuquerque (47%), Phoenix (43%), Tucson (41%), Las Vegas (32%), and Mesa (27%).

[161] Very large Hispanic American populations can also be found in the smaller cities such as Eagle Pass (96%), Las Cruces (56%), Yuma (55%), Blythe (53%), Pueblo (48%), Santa Fe (48%), and Glendale (36%).

[177][178] NASCAR has two venues within the region: The Phoenix International Raceway, was built in 1964 with a one-mile oval, with a one-of-a-kind design, as well as a 2.5-mile road course,[179] and the Las Vegas Motor Speedway, a 1,200-acre (490 ha) complex of multiple tracks for motorsports racing.