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|
|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.
|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.