The natural vegetation of the Study Area is characteristic of the Sonoran Desert Scrub (Arizona Upland Subdivision).
The dominant perennial species in this type include foothills palo verde, creosote bush, and triangle leaf-bursage along with numerous cacti from the prickley-pear. cholla, and barrel cactus groups. Landscape elements receiving additional runoff water also support more mesic species including mesquite and ironwood. Saguaro cacti also are a visually dominant component of the flora and occur principally on bajadas and mountain sides.
The annual component of the vegetation communities is also ecologically very important to wildlife species and varies greatly from year to year depending upon precipitation patterns. A significant part of the annual flora is now non-native, introduced species.
A particularly important component of the vegetation is the riparian type which occurs both near springs and along ephemeral streams. Both riparian woodlands (higher elevations and higher stream flows) and riparian scrub lands (lower elevations and lower stream flows) occur in the Study Area. Species that occur in the riparian woodland include cottonwoods, willow, and desert hackberry. Riparian scrub lands in the Study Area support populations of mesquite and higher densities of species characteristic of the surrounding upland communities.
These riparian communities play critical roles in the feeding, nesting, resting, and travel of wildlife species. While the geographic size of the riparian communities is small, their ecological importance is immense. Riparian communities form ecological corridors through the desert scrub matrix, which are both very important and very susceptible to fragmentation.