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Western Deserts
Deserts are found in areas where evaporation exceeds precipitation. High incident solar radiation as well as wind add up to a negative water budget, meaning that deserts are always dry. Far from wastelands, however, deserts are teeming with life.
The type of desert and its aridity depend on the timing and amount of precipitation. The nature of desert soil also affects availability of water for plant growth. More rain can infiltrate sandy and gravelly soils than clay soils. If rain comes as deluges, most of the water will not penetrate the soil but rather will run off the surface, and plants will receive little benefit. Many areas have saline or alkaline soils due to the constant evaporation of water, which brings minerals to the surface.
North America's four desert associations - the Great Basin, Mojave Desert, Sonoran Desert, and Chihuahuan Desert - are situated between two enormous mountain ranges, the Sierras and the Rockies. Due to their position between tall mountain ranges and the influence of the cold waters of the Pacific Ocean, the western deserts are subject to dramatic seasonal shifts in storm tracks. In the cold northern Great Basin, most of the sparse annual precipitation falls as snow. The warmer deserts to the south receive their annual precipitation as rain, either in winter or summer.
Gardeners in these regions must acknowledge the limitations of the climate, especially water. Beautiful, water-conserving, and low-maintenance gardens can be created using the desert flora.
Great Basin
The Great Basin is cold in winter and warm in summer. The elevation varies from high valleys to lofty peaks. The cold and dry landscape is less lush than other deserts, and there are fewer species. Shrubs are common, especially sagebrushes and saltbushes, as well as grasses. Locoweeds (Oxytropis species), lupines, and paintbrushes (Castilleja species) are common forbs. Pinyon pine (Pinus edulis) or Douglas-fir (Pseudotsuga menziesii) occur at higher elevations. Pronghorn antelope, jackrabbits, sage grouse, and hawks are common.
Mojave Desert
To the south of the Great Basin lies the Mojave Desert. This hot, dry desert varies from barren salt flats below sea level to forested peaks. The Mojave receives mainly winter rains. Precipitation is minimal, usually less than 6 inches per year. Yuccas, creosote bush, and beavertail cactus are common. The most conspicuous yucca is the enormous Joshua tree. The soils are generally alkaline or saline. Many of the wildflowers, such as desert marigold (Baileya multiradiata) and phacelias, are annuals. The invasive non-native tamarisks or salt cedars (Tamarix species) have taken over most stream and river banks, to the exclusion of most native species. Common Mojave fauna include bighorn sheep, coyotes, mice, sparrows, roadrunners, and lizards.
Sonoran Desert
The Sonoran desert is the most diverse and spectacular of the western deserts. This is due in large part to its subtropical climate and bi-seasonal rainfall. The wettest desert, the Sonoran receives rain from both winter and summer storms. Winter rains are slow and steady, whereas summer storms dump huge amounts of rain in a short time. There not only is a greater diversity of species, but also a greater structural diversity, with trees, shrubs, herbs, and cacti. The cacti vary from diminutive cushions to the towering saguaro. Annuals are common, and if winter rains are sufficient, the desert is blanketed with wildflowers in March and April. Reptiles abound, including the colorful gila monster, as do birds found nowhere else in North America, such as trogons and several species of hummingbirds.
Chihuahuan Desert
The Chihuahuan desert reaches its northern limits in Texas and New Mexico; most of the desert lies in Mexico. The mighty Rio Grande River cuts through the heart of the desert. The landscape is mountainous, and the valley floors are high. Winters are cold and summers are hot. The Chihuahuan gets most of its precipitation in summer. Precipitation varies between 7 and 12 inches per year. Yuccas, agaves, cacti, and annuals like Zinnia grandiflora are common. The areas where precipitation is comparatively high support grasslands. The soils are high in calcium. Pronghorns, badgers, rodents, songbirds, hawks, and reptiles are plentiful.