Deserts are rich in minerals but poor in organic material. They do not receive much rainfall. There is little leaching of the soil. Leaching is the process where rainwater moves through the soil and carries minerals deeper in the soil. The lack of rainfall also slows the decay of organic material. Deserts are divided into two main types: cool deserts and hot deserts. Cool and hot deserts result from variations in elevation and latitude that affect their winter and summer climates. Cool deserts are located on the eastern side of the Sierra Nevada and Rocky Mountains. Hot deserts are located southwest, particularly Arizona, New Mexico, and western Texas
Deserts rarely get more than 25 cm. of precipitation. Rain that falls on the desert usually runs off rather than being absorbed. The lack of moisture also affects desert temperatures. Because there is so little moisture in the air, temperatures can rise and fall dramatically, with very hot days followed by very cold nights.
Organisms that live in the desert are adapted to survive two challenges: lack of water and extreme temperatures. Plants must be able to absorb water from ground. They must prevent water loss from tissues. Spines of a cactus are an adaptation for preventing water loss by reducing the surface area from which water can evaporate. Spines also protect the plant from being eaten by predators. Cacti are called succulents, which have thick, water-filled tissues that can store water and survive long dry periods. Some desert plants have shallow roots that grow over a wide area so the plant can maximize the amount of rain it can absorb. For example the mesquite tree has roots that can draw up water as far as 20m.
The desert is home to many types of animals including insects, reptiles, birds and mammals. Desert animals get most of the water they need from their foods. All insects and reptiles have an outer coating that reduces water loss. This protective covering makes insects and reptiles well equipped to survive dryness on land. Most animals have adaptations that enable them to survive the heat. Rodents, such as the kangaroo rat, spend most of their day in underground burrows where they are protected from the heat of the sun. Animals that are active at night and sleep during the day are called nocturnal.