The Chihuahuan Desert is a desert, and an ecoregion designation, that straddles the U.S.-Mexico border in the central and northern portions of the Mexican Plateau, bordered on the west by the extensive Sierra Madre Occidental range, and overlaying northern portions of the east range, the Sierra Madre Oriental. On the U.S. side it occupies the valleys and basins of central and southern New Mexico, Texas west of the Pecos River and southeastern Arizona; south of the border, it covers the northern half of the Mexican state of Chihuahua, most of Coahuila, north-east portion of Durango, extreme northern portion of Zacatecas and small western portions of Nuevo León. With an area of about 362,000 km2 (139,769 sq mi), it is the third largest desert of the Western Hemisphere and the second largest in North America, after the Great Basin Desert.
The terrain mainly consists of basins broken by numerous small mountain ranges.
Several larger mountain ranges include the Sierra Madre, the Sierra del Carmen, the Sacramento Mountains, the Sandia-Manzano Mountains, the Magdalena-San Mateo Mountains, the Chisos Mountains, the Guadalupe Mountains, and the Davis Mountains. These create "sky islands" of cooler, wetter, climates within the desert, and such elevated areas have both coniferous and broadleaf woodlands, and even forests along drainages and favored exposures.
The Chihuahuan Desert is higher in elevation than the Sonoran Desert to the west, mostly varying from 600–1,675 m (1,969–5,495 ft) in altitude. As a result, it tends to have a slightly milder climate in the summer (though usually daytime June temperatures are in the range of 35 to 40 °C / 95 to 104 °F). Winter weather varies from relatively mild to quite cold depending on altitude and the ferocity of northerly winds. Precipitation is somewhat more abundant than most of the southern Great Basin, the Sonoran, and Mojave deserts, however it is still usually less than 254 millimeters (10.0 in) per year, with much of the rain falling during the "monsoon" of late summer. The mean annual precipitation for the Chihuahuan Desert is 235 mm (9.3 in) with a range of approximately 150–400 mm (6–16 in). Nearly two-thirds of the arid zone stations have annual totals between 225 and 275 mm (8.9 and 10.8 in). Snowfall is scant except at the higher elevation edges.