Photo by Pete Gregoire
Wrapping around the northern end of the Gulf of California (from northwestern Baja California, Mexico through southeastern California and southwestern Arizona to western Sonora, Mexico) the Sonoran Desert covers approximately 100,000 square miles.
Considered the wettest desert in the world, the Sonoran is the only place on the planet where the saguaro cactus grows in the wild.
The amount and seasonality of rainfall are considered to be the defining characteristics of the Sonoran Desert. Much of the region has a biseasonal rainfall pattern, although even during the rainy seasons most days are sunny. From December to March, frontal storms from the northern Pacific Ocean occasionally bring widespread, gentle rain to the northwestern portion of the Sonoran Desert -- including Tucson and Saguaro National Park. From July to mid-September, the summer monsoon brings surges of wet tropical air and frequent, but localized, violent thunderstorms.
The other three North American deserts -- the Mojave, Chihuahuan, and Great Basin -- also occur in Arizona . . . the only state in the U.S. to have all four. The Sonoran Desert differs from the other three deserts in that it has mild winters; most of the region rarely experiences frost. About half of the biota is tropical in origin, with life cycles attuned to the brief summer rainy season. The winter rains, when ample, produce large populations of annuals (which comprise about half of the species in the Sonoran Desert's flora). Altogether, the Sonoran Desert includes approximately 60 mammal species, 350 bird species, 20 amphibian species, more than 100 reptile species, 30 native fish species, and more than 2,000 native plant species.
From arid desert to lush coniferous forest, the incredible diversity of plant and animal life in the Sonoran Desert is exemplified withinSaguaro National Park.
The establishing legislation for the Park identifies "prime Sonoran Desert habitat, including exceptionally rich areas of saguaro cactus and palo verde uplands" as essential resources of Saguaro National Park. The NPS interprets this in an ecological context to mean not individual cacti, but rather the interrelated plants and animals that make up the Sonoran Desert ecological community.
