Geography, Climate, Life Zones

The Sonoran Desert reaches from central Arizona down into Mexico and Baja, California.   It is called the Sonoran Desert because much of it is located in the state of Sonora, Mexico.

The Sonoran Desert, a subtropical desert located in the Southwestern climatic zone, is the world's only desert with two "rainy seasons".

                       Summer, July-September

Brief, intense, compact, "monsoon" storms originate in the Gulf of  Mexico andarrive from the south.   Clouds like those pictured lower left build along the Mongolen Rim to the northeast.  Tropical storm cells sweep across the desert. Often these storms are followed by a rainbow as shown in these photographs donated by volunteer Howard Meyers.Click on the pictures to enlarge them.

Monsoon Storms
[monsoon clouds] [lightening bolt] [rainbow]

 

                         Winter, December-March

Storms last longer, cover more area, have gentle rain, originate in the Pacific      Ocean and arrive from the north. These cloudy days are unusual here in the       Valley of the Sun.

                         Annual Rainfall: 7" to 16.4"

                        Average Temperatures:

                         January:     51.8 degrees F.

                         April:          65        "

                         October:     70.6   "

                         July:            85.9           "

Life Zones

Arizona's plant life spans six main life zones from a low point of 70 feet near Yuma to a high point of 12,670 feet in the San Francisco Peaks near Flagstaff.  The Desert Foothills Scenic Drive is located in the Lower Sonoran Life Zone.

The Lower Sonoran Zone is situated below 4,500 feet where creosote, jojoba, paloverde, mesquite, bursage and cacti abound. The plants in this zone can endure high temperature and low precipitation.

Willing to Wait

Spring annuals survive as seeds, some for decades.  When temperatures are right and rainfall in the fall and winter (January and February) is sufficient, the seed germinate. These types of plants are referred to as ephemerals (of very short duration).   They develop quickly, blossom and soon go to seed.

Many Survival Techniques

Paloverde, mesquite, ironwood, and bursage survive desert conditions because of their reduced leaf area.  Others, such as the jojoba and creosote, have specialized leaves for desert survival, while the ocotillo shed all their leaves during periods of drought. Still others, such as the cacti (saguaro, barrel; etc.) and certain bushes, have vestigial leaves or have modified their leaves to spines over evolutionary time.  

Arizona's Unmatched Diversity

The other five Arizona life zones support different types of plants.   Visitors from New England and the Northwest will feel more at home in these area.  

Arizona's Life Zones
Upper Sonoran Zone Ranges from 4,500 to 6,500 feet. Increased levels of rainfall support grasslands, sagebrush and woodlands of pine, oak and juniper.   Here, too, lie large areas of chaparral with thickets of manzanita.
Transition Zone Between 6,500 and 8,000 feet. Characterized by large stands of ponderosa pines. Scattered between the pines you will find junipers, Gambel oaks, and Douglas firs.
Canadian Zone Ranges from 8,000 to 9,500 feet.  Cooler temperatures and increased moister support forests of fir trees.  The Douglas fir dominates this zone, with a mixture of blue and Engelmann spruce, quaking aspen, and white fir.
Hudsonian Zone Between 9,500 to 11,500 feet. The trees that grow here, spruce, fir and bristlecone pines, are stunted as the result of a short growing season. Wind at these higher elevations often causes the trees to be twisted.
Alpine Zone Above 11,500.  This zone, which is above the timberline,  is found in the San Francisco Peaks and is characterized by lichens, sedges, grasses and alpine wildflowers.