Southwestern United States

Lore & Background

The geography of the region is mainly made up of four features: the Mojave, Sonoran, and Chihuahuan Deserts, and the Colorado Plateau; although there are other geographical features as well, such as a portion of the Great Basin Desert. Formed approximately 8000 years ago, the Chihuahuan Desert is a relatively dry desert, although it is slightly wetter than the Sonoran Desert to the west. It spreads across the southeastern portion of the region, covering from southeastern Arizona, across southern and central New Mexico, and the portion of western Texas included in the Southwest. While it is the second largest desert in the United States, only a third of the desert is within the United States, with the rest in Mexico. The Chihuahuan is a 'rain shadow' desert, formed between two mountain ranges (the Sierra Madre Occidental on the west and the Sierra Madre Oriental on the east) which block oceanic precipitation from reaching the area. The Chihuahuan Desert is considered the 'most biologically diverse desert in the Western Hemisphere and one of the most diverse in the world,' and includes more species of cacti than any other desert in the world. The Sonoran Desert makes up the southwestern portion of the Southwest; most of the desert lies in Mexico, but its United States component lies on the southeastern border of California, and the western 2/3 of southern Arizona. Its most widely known inhabitant is the saguaro cactus, which is unique to the Sonoran. The Mojave Desert is the smallest, driest and hottest desert within the United States. The Colorado Plateau varies from the large stands of forests in the west, including the largest stand of ponderosa pine trees in the world, to the Mesas to the east. The most dramatic example of its canyons is the Grand Canyon.

Reader's Guide

Distinct elements of the Western lifestyle thrive in the region, such as Western wear and Southwestern cuisines, including Native American, New Mexican, and Tex-Mex, or various genres of Western music like Indigenous, New Mexico, Bluegrass, and Tejano music styles. Likewise with the sought-after Southwestern architectural styles in the region inspired by blending Pueblo and Territorial styles, with Mediterranean Revival, Spanish Colonial architecture, Mission Revival architecture, Pueblo Deco, and Ranch-style houses in the form of the amalgamated Pueblo Revival and Territorial Revival architectures. This is due to the region's caballero heritage of the Native American (especially Apache, Pueblo, and Navajo), Hispano, Mexican American, and frontier cowboy. The elevation in the Chihuahuan Desert varies from about 1,750 to 6,000 feet (500 to 1,800 meters), as well as several larger mountain ranges within or bordering this desert including the Black Range, Organ Mountains, Capitan Mountains, Manzano Mountains, Sacramento Mountains, Sandia Mountains, Magdalena Mountains, and Chiracahua Mountains. The sky islands in the Chihuahuan Desert supply the surrounding desert foothills with flowing water during the spring runoff and after the summer storms of the New Mexican monsoon season. The Sonoran Desert is the most populated area within the region, with six of the top ten major population centers found within its borders: Phoenix, Tucson, Mesa, Chandler, Glendale, and Scottsdale, all in Arizona. The Mojave Desert within the region includes Las Vegas as the most populous city. Human history in the Southwest begins between 19,000 and 21,000 years BCE (21,000 to 23,000 years before present), with a group of likely hunter-gatherers whose presence is recorded in the White Sands footprints. Material culture remains appear with the arrival of the Clovis culture around 9000 BCE, which gave way to the Folsom tradition in New Mexico.

Did You Know?

• The Chihuahuan Desert is considered the 'most biologically diverse desert in the Western Hemisphere and one of the most diverse in the world,' and includes more species of cacti than any other desert in the world.
• The saguaro cactus, unique to the Sonoran Desert, is its most widely known inhabitant.
• The Mojave Desert is the smallest, driest and hottest desert within the United States.
• The Colorado Plateau includes the largest stand of ponderosa pine trees in the world.
• Human history in the Southwest begins between 19,000 and 21,000 years BCE, recorded in the White Sands footprints.

Territorial Formation and the Puzzle of Boundaries

The Southwestern United States carries a layered territorial history that resists a single clean definition. For centuries, much of this land belonged to New Spain and later Mexico, with the historical province of Santa Fe de Nuevo México anchoring settlement in New Mexico's pueblos and scattered Spanish or Mexican municipalities. Outside those small communities, the vast stretches of what is now the Southwest remained largely uninhabited. The modern American claim to the region crystallized in two pivotal moments: the Treaty of Guadalupe Hidalgo in 1848, which transferred the bulk of the territory to the United States, and the smaller Gadsden Purchase of 1854, which added a final strip of land. Even today, no official boundary demarcates the Southwest. Scholars and geographers have proposed various lines—stretching from the Mojave Desert at 117° west longitude to Carlsbad, New Mexico, at 104° west, or from the Mexico–United States border northward to roughly 39° north latitude. Some definitions narrow the core to just Arizona and New Mexico, while others trace the old borders of the Nuevo México Province or the later American New Mexico Territory. This ambiguity means the Southwest remains as much a cultural idea as a fixed map.

Desert Landscapes and Extraordinary Biodiversity

The Southwest's terrain is defined by four major features: the Mojave, Sonoran, and Chihuahuan Deserts, plus the Colorado Plateau. Deserts dominate the southern and western reaches, while the high-desert plateau rises north of the Mogollon Rim. The Colorado River threads through the north and west, and the Rio Grande runs north to south along the eastern side. The Chihuahuan Desert, formed roughly 8,000 years ago, stretches across southeastern Arizona, southern and central New Mexico, and western Texas. It ranks as the second-largest desert in the United States, though only about a third of its expanse lies within American borders. Caught in the rain shadow between the Sierra Madre Occidental and Sierra Madre Oriental, it receives scant oceanic moisture. Yet it is regarded as the most biologically diverse desert in the Western Hemisphere and one of the most diverse on Earth, with more cacti species than any other desert. Above the plains, forested and sometimes snow-capped ranges form sky islands—pockets of radically different life that also deliver spring runoff and monsoon water to the desert below. West of the Chihuahuan, the Sonoran Desert holds the most diverse plant community of any desert worldwide, crowned by the saguaro cactus, which grows nowhere else.

The Caballero Heritage and a Composite Culture

The Southwest's cultural identity is a living mosaic forged from multiple heritages that have interwoven over time. At its heart sits the caballero tradition, a blend of Native American—particularly Apache, Pueblo, and Navajo—Hispano, Mexican American, and frontier cowboy lineages. This layered heritage shows up in everyday life through distinctive Western wear and a rich culinary scene spanning Native American, New Mexican, and Tex-Mex traditions. Music in the region reflects the same multiplicity. Indigenous musical forms sit alongside New Mexican styles, Bluegrass, and Tejano, each carrying its own rhythms and histories. Together they create a soundscape that is neither purely Anglo-American nor a single ethnic expression, but something genuinely composite. Architecture tells a parallel story. The region's most sought-after building styles draw from Pueblo and Territorial roots, then layer in Mediterranean Revival, Spanish Colonial, Mission Revival, and Pueblo Deco influences. Ranch-style homes represent yet another thread. In practice, many of the most beloved structures amalgamate Pueblo Revival and Territorial Revival elements into a single design language, producing a built environment that feels simultaneously ancient and modern, indigenous and imported. The result is a regional aesthetic that resists easy categorization, remaining deeply tied to the land and its peoples.

Urban Growth in an Arid Landscape

Before 1848, human settlement across most of the Southwest was virtually nonexistent outside New Mexico's pueblos and a scattering of Spanish or Mexican municipalities. The region's urban story is therefore relatively young, yet it has produced some of the country's largest metropolitan areas. Today, the five biggest metro centers are Phoenix, Las Vegas, El Paso, Albuquerque, and Tucson. The Sonoran Desert portion of the Southwest is by far the most densely populated area in the region. Six of the top ten major population centers fall within its borders: Phoenix, Tucson, Mesa, Chandler, Glendale, and Scottsdale, all in Arizona. Yuma and Prescott, also in Arizona, complete the list. This concentration makes the Sonoran Desert's U.S. component the demographic engine of the entire Southwest. The Chihuahuan Desert, by contrast, supports a more scattered urban pattern. El Paso and Albuquerque serve as its major American cities, with smaller centers like Las Cruces and Roswell in New Mexico and Willcox in Arizona dotting the landscape. The Mojave Desert occupies the most northwestern corner of the region, bordered to the south by the Sonoran and to the east by the Colorado Plateau.