Near the edge of major Basin and Range formation, about six million years ago, a severe sideways ripping action began along the Pacific coastline; this continues in our own time [San Andreas fault].

Earthquakes
...The Sonoran Desert is seismically quiet...

The Pleistocene Climate
The last permanent high-elevation ice masses were rapidly melting about 14,000 years ago, and the regional climate was becoming drier and modern (interglacial) by 12,000 years ago. This last climate change marks the birth of the modern Sonoran Desert ecosystem.

Landforms
Layered volcanic bedrock
crystalline bedrock
alluvial fan - debris flown downhill from mountains by rare, heavy rains that produce torrents of mud, rocks, and vegetation
stream terraces
floodplain
pediment -- buried shoulders of mountain rock
basin and range faults
stream through valley
gravel
sand and mud
schist
insleberg -- isolated small hills of exposed rock masses near mountains
granite bedrock
bajada or piedmont -- coalescence of neighboring alluvial fans
terrace gravels

Since the 1890's, river floods have tended to widen the [valley] channels, so that the floodwaters do not flow out onto the floodplains, except locally.

This post-1890's channel enlargement is part of the regional trend throughout the West called "arroyo cutting," likely caused by a combination of factors, including increased cattle grazing following development of regional railroads in 1882, devegetation of hillsides by the mining industry for mine timbers and coke, and a possible unrecognized, subtle-climate shift.

Haphazard bank stabilization increases channel erosion (bank caving) and floodplain inundation downstream of the protected reaches. This is because cement-lined channel walls prevent infiltration and force more water down the channel.

Desert pavement is a sparsely vegetated desert flatland totally covered with a single layer of desert-varnished rocks. Desert varnish is a black, shiny coating on the exposed surfaces of undisturbed rocks.

Sonoran Desert Region Natural History
Hints of profound relations are everywhere around us: storm tracks funneled by Basin and Range topography, which ultimately define the region's ecological limits; the very different past worlds represented in the fossil record; hard granite rocs torn apart by small lichen colonies; the wide variety of landforms and rock types.  ...the often-neglected third dimension is vital, as miners, soil engineers, and water well drillers know. All these effects of the past are interwoven into a tapestry of cause and effect on a grand and wondrous scale.