Death Valley lies in the Basin and Range region, where the pulling apart of Earth's crust let blocks of land slide along faults, forming alternating valleys and mountain ranges, and it is a long, narrow basin 282 feet, or 86 meters, below sea level, walled in by high, steep mountain ranges. It is dry because it sits in the rain shadow of mountains, and a rain shadow desert forms on the far side of a mountain range, where the air has already lost its moisture. Its salt pan formed as rain dissolved minerals from rocks, flowed downhill to temporary lakes, and then evaporated, leaving the salts behind.

The records from the valley show how extreme a desert can be. As of November 2026, the hottest air temperature ever recorded in Death Valley was 134 degrees Fahrenheit, or 57 degrees Celsius, on July 10, 1913, and the driest stretch on record was only 0.64 inches, or 1.6 centimeters, of rain over a 40-month period in 1931 to 1934. Death Valley is so hot partly because heated air rises, cools, and is recycled back down to the valley floor, where it is compressed and heated even more, and in deserts about 90 percent of the day's accumulated heat radiates back toward the sky after sundown, which makes daily temperature ranges of 50 degrees or more. In the desert heat, people should drink plenty of water and stay in the shade during the hottest part of the day.

Dunes record the wind that built them, because simple dunes show a wind that has not changed in strength or direction since they formed, while compound and complex dunes suggest the wind has changed. Parabolic dunes are U-shaped, with arms that trail behind because vegetation has fixed them in place while the bulk of the sand migrates forward. The most common dune form on Earth and on Mars is the crescentic dune, and linear dunes are sand ridges much longer than they are wide and may be more than 160 kilometers long. Star dunes grow upward rather than sideways; in China's Badain Jaran Desert they reach up to 500 meters and may be the tallest dunes on Earth, although sand dunes cover only about 10 percent of the world's deserts.

Desert animals manage scarce water through physiology as well as behavior. A dromedary camel lets its body temperature swing from 34 to 41.7 degrees Celsius through the day, so it can avoid sweating as the outside temperature rises, and a camel can lose a lot more of its body water than most mammals and still survive. A kangaroo rat does not need to drink, because it gets its water from the seeds it eats and its kidneys and droppings are built to waste almost none, and it lives in deep underground burrows that it seals off to keep out midday heat and to recycle the moisture from its own breath. Some tiny desert animals survive drying out by cryptobiosis: they can lose up to 92 percent of their body water and recover in as little as half an hour once rehydrated. The Gila monster, a venomous lizard that spends more than 90 percent of its life below ground, uses its venom mainly for defense, and prey are rarely envenomated. You may have heard that a camel stores water in its hump; in fact, a camel's hump is made of fat, not water.

Most deserts are not empty and lifeless; they are home to a variety of plants, animals and other organisms. As of November 2026, about one-third of Earth's land surface is desert, and fossil desert sediments as much as 500 million years old have been found in many parts of the world. During the African Humid Period, roughly 11,000 to 5,000 years ago, the Sahara was likely far wetter and greener, with vegetation, wetlands and perhaps even large lakes. After a big rain, flowers can bloom in the desert.

Words to know

• parabolic: U-shaped
• dromedary: one-humped camel
• cryptobiosis: hidden life
• envenomated: injected with venom
• faults: crust cracks