Chihuahuan Desert: Arizona, Texas, Mexico

The same forces that have shaped the other North American deserts by creating the geologically stretched Basin and Range Province also forged the 280,000-square-mile (450,616 sq km) Chihuahuan Desert. This great desert plain punctuated with a patterned scattering of northsouth trending mountains starts in the shadow of the massive Sierra Madre in Mexico, runs north into Texas and New Mexico, and finally into the southeastern corner of Arizona.

A rain shadow desert of summer storms and winter droughts, the Chihuahuan Desert harbors remarkably well-adapted creatures, tenacious plants dominated by yuccas, and geological marvels like the limestone Carlsbad Caverns, the blinding gypsum sand dunes of White Sands, and the meanders of the Rio Grande River.

The Chihuahuan neatly rounds out the climatic range of North American deserts. It is the largest and highest on average, with an average elevation of 4,000 feet (1,219 m). It also lies deep in the rain shadow of the massive Sierra Madre range, a jagged wilderness of tormented rock created by the uplift of continental collisions that started 65 million years ago as the supercontinent of Pangea gradually broke up and scattered across the globe, propelled by the constant movement of tectonic plates. Those same forces built the Rocky Mountains farther north and ultimately pasted onto the leading edge of North America the areas that now comprise California, Washington, and Oregon. The towering Sierra Madre cut off most winter rains in the Chihuahuan Desert, so the region's 8–14 inches (203–355 mm) of rainfall come almost entirely in the summer. The long, hot dry season in the Chihuahuan stretches from October to early June. That neatly reverses the rainfall pattern in the cold Great Basin Desert, with its freezing winter rains and snow. As a result, the Chihuahuan has a greater diversity of plants and wildlife than the Great Basin, but far less than the Sonoran, which has alternating winter and summer rains.

The effects of the Sierra Madre on climate largely account for the presence of the Chihuahuan Desert. Wet storms sweeping in from the Gulf of California and the Pacific Ocean break against the western flank of those stone ramparts, which wring out the moisture as clouds rise into the colder, higher altitudes or deflect storms northwest into the Sonoran Desert. On the east side of the 13,000-foot-tall (3,962 m) Sierra Madre, chilled, dry air flows down into the Chihuahuan's desert basins, gaining enough energy from compression as it drops to heat up by about 4 degrees for every 1,000 feet (304 m). The resulting hot, dry winds sustain this unique desert.

Much closer to the equator than the other North American deserts, the clear, dry air of the Chihuahuan offers little resistance to the Sun's rays. The ground heats up quickly in the daytime, since 90 to 95 percent of the Sun's energy reaches the ground. By contrast, clouds and haze in the form of water vapor typically block half the Sun's energy in more humid places. That same lack of moisture in the desert air allows the infrared heat radiating off the ground at night to escape quickly back into the atmosphere. As a result, the Chihuahuan Desert typically has hot days and cold nights, with temperature swings of 45 degrees in a single day. The uneven rainfall combined with the cold winters restrict the plant life of the Chihuahuan Desert, so it lacks the signature Joshua tree of the Mojave or the frost-sensitive saguaro of the Sonoran. On the other hand, it has more variety in plant life than the sagebrush plains of the Great Basin. Varieties of yucca and century plant are the defining plants of the Chihuahuan Desert.