The desert is a dry, hot, and sometimes waterless place that is very vast. Deserts take up 8.6 million square miles (22 million square kilometers) of the earth's surface. Deserts receive less than 10 inches (25 centimeters) of rain annually. One of the driest deserts in the world is the Atacama Desert. This desert acquires below one inch (2.5 centimeters) a year. Some of the worlds largest deserts, the Sahara, Australian, and the Arabian, lie between latitude 30° south and latitude 30° north. This latitude belt has constant high pressure, which keeps low-pressure air that forms rain clouds, out of the area.

Most deserts are very hot. In Death Valley, a part of the Mojave Desert, temperatures are known to reach 190° F (88° C). The Great Basin desert, however, is at a higher elevation and can get very cold in the winter. Even hot deserts can get cold during the night, because hot air dissipates very quickly once the sun goes down.

The Mojave and the Great Basin in the southwestern United States are sheltered by mountain ranges, which stop rain clouds from advancing into the deserts.