The Sonoran Desert

2/12/12

Saguaro cactus

     North America has four deserts:  Great Basin, Mohave, Chihuahuan and Sonoran.  I live in the Sonoran Desert that runs from the state of Sonora, Mexico up through southern Arizona to the Phoenix area, and west to sourtheastern California through Baja California.  The Sonoran Desert covers 100,000 (260,00 sq km).

     The Sonoran Desert differs from the three other North American deserts in that it has mild winters.  Frosts are few or rare in some parts of the Sonoran Desert.  My area had six nights of  below freezing weather last winter, but we have had only two nights below freezing so far this year.  Another defining characteristic of the Sonoran Desert is the bi-seasonal rainfall pattern.  The area gets gentle rains from December to March from storms originating in the North Pacific.  From July to mid-September, the summer monsoon brings violent thunderstorms and localized deluges.

Organ Pipe cactus

         There are six subdivisions of the Sonoran Desert based on distinctive vegetation.  I live in the hottest and driest subdivision called the Lower Colorado River Valley area (although the Colorado River is 180 miles from where I live).  Summer highs can exceed 120 F (49 C), and surface temperatures can near 180 F (82 C) from the intense solar radiation from cloudless skies.  My area of the Sonoran Desert gets the least amount of rain, from three to eight inches a year.  Last year we had four inches of rain.  The terrain consists mostly of broad, flat valleys with widely-scattered, small mountain ranges of almost barren rock.  There are many areas of loose sand.

Velvet Mesquite tree

     I have read that this desert supports a surprising 2,000 species of plants.  Two species distinguish the Sonoran Desert from other North American deserts:  legume tress and columnar cactus.  Examples of columnar cactus include the Organ Pipe cactus and the Saguaro cactus shown above.  The Sonoran Desert is the only place in the world where the Saguaro cactus grows in the wild.  Legume trees that grow here include the mesquite and acacia.  Trees grow only along the larger dry washes, even though the wash may carry water for only a few hours or days a year.





Creosote bush





  











White Bursage bush

     The valleys are dominated by low shrubs, primarily Creosote bush and White Bursage.  These are the two most drought-tolerant plants in North America.

Desert Globemallow

Indian Paintbrush

      We do have some spring wildflowers, such as Desert Globemallow and Indian Paintbrush.  Though desert plants must cope with scarce water, it is a misconception that they struggle to survive.  The native species are adapted to and thrive under desert conditions.