Chihuahuan Desert

This desert has wide valleys with mountains around them.

Long ago it was wetter here. Forests grew on the mountains.

The Park Service describes the desert's shape as basin and range: wide desert valleys, called basins, with mountains, called ranges, around them. Rain that falls in a closed basin cannot flow out, so salt lakes called playas can form. Dunes of quartz or gypsum sand are common too.

About 9,000 years ago, the NPS says, this area was wetter, and forests covered the mountain slopes. As it dried out, plants and animals were cut off from one another, and over time this led to the special plants and animals of the desert today.

NPS: basin-and-range topography of broad desert basins bordered by terraces, mesas and mountain ranges; rainwater drains internally in closed basins, so salt lakes (playas) can form; quartz and gypsum dune fields are common.

About 9,000 years ago the region was wetter, with forest-dominated slopes; as it dried, species experienced isolation, differentiation and sometimes extinction, which led to today's distinctive Chihuahuan flora and fauna. The NPS adds that the eastern boundary is one of the oldest and richest centers of plant evolution in North America.

Thousands of kinds of plants grow here, with lots of cacti.

Pronghorn, javelinas, prairie dogs and golden eagles live in this desert.

The NPS says the desert has as many as 3,500 kinds of plants, including nearly a quarter of all the world's cactus species, and about 1,000 plant species grow nowhere else. There are yucca woodlands, wide desert grasslands and many yuccas and agaves.

More than 130 kinds of mammals live here, such as mule deer, pronghorn, javelina and gray fox, along with more than 170 kinds of amphibians and reptiles and around 400 kinds of birds.

NPS: up to 3,500 plant species, nearly a quarter of the world's cacti, about 1,000 endemic plants; desert shrublands at low elevations to conifer woodlands at the highest; yucca woodlands, playas, gypsum dunes and freshwater habitats. Over 170 amphibians and reptiles (at least 18 endemic); nearly half of 110 fish species endemic or of limited range, mostly relics in isolated springs of closed basins.

Over 130 mammals (mule deer, pronghorn, jaguar, javelina, gray fox), North America's largest remaining black-tailed prairie dog complex and the only populations of the endemic Mexican prairie dog; about 400 bird species; grasslands are wintering grounds for many Great Plains birds.

Summers here are hot. Winters can be cold.

Much of the rain falls in summer storms.

The Chihuahuan Desert gets more summer rain from monsoon thunderstorms than the Sonoran and Mojave deserts, and it has colder winters, the NPS explains. Each year it gets about 150 to 500 millimeters of rain.

Much of the desert is high: the White Sands National Park page says a large part lies above 4,000 feet (about 1,200 meters), and that in its northern parts nights fall below freezing about 100 times a year on average.

NPS network page: hot summers and cool to cold, dry winters; 150-500 mm of precipitation a year, much of it as summer monsoon rain; more summer rain and colder winters than the Sonoran and Mojave deserts.

NPS White Sands page: elevations from near 1,000 ft along the Rio Grande in Texas to 10,000 ft in Mexico's mountains, with a large portion above 4,000 ft; nighttime freezes average about 100 a year in the northern latitudes, and temperatures can reach 122 °F (50 °C) in some regions.

Deserts can be hot, and they can be cold too. Bring a jacket and a hat.

Rest in the shade when it is hot.

The CDC says deserts can bring both heat and cold problems, because the temperature swings widely. In heat, it suggests light, loose, light-colored clothing, a wide-brimmed hat and drinking during exercise, and avoiding hard activity in the hottest part of the day.

The NPS lists threats to the desert's plants and animals, including overgrazing, using up water, cities spreading and people collecting native plants and animals.

CDC Yellow Book: environments with wide temperature swings, such as deserts, carry risk of both heat and cold illness; wear lightweight, loose, light-colored clothing and a wide-brimmed hat (which markedly reduces radiant heat); drink during exertion (thirst alone does not prevent mild dehydration, but forced drinking risks hyponatremia); avoid strenuous activity in the hottest part of the day.

NPS: threats include overgrazing, water depletion and diversion, changed fire regimes, urbanization, agricultural and resource-extraction growth, invasive species and overcollecting of native plants and animals; it calls the ecoregion one of the most endangered in the world.