North America's Deserts

Sonoran, Mojave and the Great Basin deserts are included in what geomorphologists call the Basin and Range Province.

• Consists of a series of many basins interrupted with mountain ranges.
• These basins, or playas have no drainage.
• During the wet cycles they become shallow playa lakes which may last from a few months, years or longer.
  Great Basin flooded and produced Lake Lahotan-evaporated over 12,000 years leaving a few salty lakes behind.
• The areas between the desert ranges have been filled with water washed alluvium. This alluvium, or fine soil, produces the flat spaces usually associated with deserts.
• The water table may be high in the flatlands and drainage is slow. These poorly drained patches and larger playas become alkaline through accumulation of soluble chemicals
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1. Sonoran-Hottest NA desert

• Bimodal rainfall patterns cause high biodiversity.
• Spectacular spring flowers.

The Sonoran Desert is an arid region covering 120,000 square miles in southwestern Arizona and southeastern California, as well as most of Baja California and the western half the state of Sonora Mexico.

This is the hottest of our North American deserts, but a distinctly bimodal rainfall pattern produces a high biological diversity. Winter storms from the Pacific nourish many West Coast annuals such as poppies and lupines, while well-developed summer monsoons host both annuals and woody plants originating from the south. Freezing conditions can be expected for a few nights in winter.

Trees are usually well developed on the desert ranges and their bajadas. Often abundant on these well-drained soils are Little-leaf Paloverdes, Desert Ironwoods, Catclaw and Saguaro.

Extreme variation in daily temp

The transition from the hot Sonoran Desert to the cooler and higher Great Basin is called the Mojave Desert. This arid region of southeastern California and portions of Nevada, Arizona and Utah, occupies more than 25,000 square miles.

On the northwestern boundary it extends from the Sierra Nevada range to the Colorado Plateau in the east; it abuts the San Gabriel-San Bernardino mountains in the southwest. Near the Great Basin-Mojave border lies Death Valley, the lowest point in North America and a national park.

The Mojave's desert climate is characterized by extreme variation in daily temperature and an average annual precipitation of less than 5 inches. Almost all the precipitation arrives in winter. Freezing temperatures occur in winter, while summers are hot, dry and windy.

The Mojave has a typical mountain-and-basin topography with sparse vegetation. Sand and gravel basins drain to central salt flats from which borax, potash and salt are extracted. Silver, tungsten, gold and iron deposits are worked.

While some do not consider the Maojave a desert in its own right, the Mojave Desert hosts about 200 endemic plant species found in neither of the adjacent deserts.Cactus are usually restricted to the coarse soils of bajadas. Mojave Yucca and, at higher elevations Desert Spanish Bayonet, a narrow-leafed yucca, are prominent. Creosote Bush, Shadscale, Big Sagebrush, Bladder-sage, bursages and Blackbush are common shrubs of the Mojave Desert.

Occasional Catclaws grow along arroyos. But, unlike the Sonoran Desert, trees are few, both in numbers and diversity. The exception is the Joshua-tree. While this unusual treelike yucca is usually considered the prime indicator of Mojave Desert vegetation, it occurs only at higher elevations in this desert and only in this desert.

3. Chihuahuan-Plateau 1,000-5,000 ft: from: http://www.desertusa.com/du_chihuan.html

Most of the Chihuahuan Desert -- the largest desert in North America -- lies south of the international border, but it extends into parts of New Mexico, Texas and even sections of southeastern Arizona. Its minimum elevation is above 1,000 feet, but the vast majority of this desert lies at elevations between 3,500 and 5,000 feet. Winter temperatures are cool, and summer temperatures are extremely hot. While some winter rain falls, most precipitation occurs during the summer months. Limestone and calcareous soils are characteristic.

The biological diversity of perennial plant life is relatively low. Like the Great Basin Desert, this is a shrub desert. Yuccas and agaves, growing with grasses and often Creosote Bushes, give this desert its characteristic appearance. Prickly-pears and Mormon Tea also contribute. Tarbush is sometimes a dominant shrub. Honey Mesquite grows along washes and playas. White-thorn Acacia, Allthorn and Ocotillo are other large, conspicuous plants here.

4. Great Basin-Largest US. desert

• Cold desert 3,000-6,500 ft
• Vegetation low and homogeneous, single dominant bush for miles

The Great Basin Desert, the largest U. S. desert, covers an arid expanse of about 190,000 square miles and is bordered by the Sierra Nevada Range on the west and the Rocky Mountains on the east, the Columbia Platea to the north and the Mojave and Sonoran deserts to the south.

• This is a cool or "cold desert" due to its more northern latitude, as well as higher elevations (at least 3,000 feet, but more commonly from 4,000 to 6,500 feet). Precipitation, generally 7-12 inches annually, is more evenly distributed throughout the year than in the other three North American deserts. Winter precipitation often falls as snow.

  Playas are a conspicuous part of this desert, due to its recent geological activity. In notable contrast to the other three deserts, Great Basin vegetation is low and homogeneous, often with a single dominant species of bush for miles. Typical shrubs are Big Sagebrush, Blackbrush, Shadscale, Mormon-tea and greasewood. There are only occasional yuccas and very few cactus.

  The Colorado Plateau, centered in northeastern Arizona, and including the adjacent Four Corners region of Utah, Colorado and New Mexico, is sometimes included in the Great Basin Desert, sometimes considered a separate desert -- the Navajoan -- and sometimes not considered a true desert. The Plateau includes large barren areas, spectacular geological formations, more juniper and pinyon trees and generally higher elevations..

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