The Arizona Upland has been described as "aridified thornscrub" in reference to its origins in Sinaloan thornscrub and tropical deciduous forest, its ecological progenitors to the south.
The Sonoran Desert boasts a remarkable variety of reptiles. Derived from both temperate and tropical origins, the natural history of these resilient animals reveal the complex history of the Sonoran Desert itself.
Actually, few reptiles are endemic to the Sonoran Desert. Most have broad geographic ranges and are not restricted to specific biogeographic subdivisions.
The Arizona Upland is the richest of these subdivisions in terms of reptile diversity with 3 turtle, 17 lizard, and 21 snake species recorded in the vicinity of Tucson, Arizona alone.
Some of the reptiles reflect miocene links with neotropical dry forests.
Driven by bi-seasonal rainfall, this particularly rich desert community, visually characterized by the familiar saguaro and foothills paloverde, occurs primarily on rocky slopes and bajadas from about 1,800 to over 4,000 feet in elevation.
The gradual transition at the elevational edges of the Arizona Upland produces an interesting blend of flora and fauna.
The gently sweeping alluvial bajadas provide avenues of upward dispersal for a few more mobile Lower Colorado Valley species.
Biotic elements from semi-desert grassland, oak woodland, and upland riparian canyons descend to about 3,000 feet.
As demonstrated by its lizard and snake diversity, The Arizona Upland is clearly the richest biotic subdivision of the Sonoran Desert.
It remains the classic image of the Sonoran Desert in the minds of most people...
...even though its biotic character often reflects a closer relationship with tropical dry forest communities than with other faces of the Sonoran Desert itself.