Deserts cover about one fifth of the Earth's surface and occur where rainfall is less than 50 cm/year. Although most deserts, such as the Sahara desert and the deserts of the southwestern U.S., Mexico, and Australia, are locateed at low latitudes, another kind of desert, cold deserts, are located in the basin and range area of Utah and Nevada and in parts of western Asia. Most deserts have a small amount of unique vegetation, as well as specialized animals. Soils often have lots of nutrients because they need only water to become very productive and have little or no organic material. Weather are common in cold weather, and sudden, infrequent, but intense rains that can cause flooding.