The higher, slightly cooler, and wetter Mojave Desert is the special habitat of the Joshua tree, extensive stands of which occur throughout the western half of the park. Proclaimed a National Monument 10 August 1936 by President Franklin D. Roosevelt and redesignated a National Park 31 October 1994. Designated a Biosphere Reserve 1984. The desert is immense and infinitely variable, yet delicate and fragile. It is a land shaped by sudden torrents of rain and climatic extremes.
Rainfall is sparse and unpredictable.
Streambeds are usually dry and water holes are few. This land may appear lifeless, but within its parched environment are intricate living systems, each fragment performing a slightly different function and each fragment depending upon the whole system for survival. Two deserts, two large ecosystems whose characteristics are determined primarily by elevation, come together at Joshua Tree National Park. Few areas more vividly illustrate the contrast between high and low desert. Below 3,000 feet, the Colorado Desert, occupying the eastern half of the park, is dominated by the abundant creosote bush.