Desertification Factors: Elements: Earth, Wind, Fire, Rain, Love, [air, light, rain,soil]

1. Geologic: soil/salt [Ca/Na], ice/glacial ebb [interglacial], time/pleistocene:150mya-holocene;11kya, pressure

2. Topographic: biome, flora, fauna

3. Climatic: weather, climate, water, temperature

4. Hydrologic

Modern desert communities have been present for only about five percent of th 2.4 million years of the Peistocene, while ice age woodlands in the desert lowlands persisted for about 90% of this period.

Great summer rainfall would suggest, tropical oceans were warmer than they are today.

As far as many large animals, the modern distribution may not accurately reflect their physiological range limits because of human predation in the last 11,000 years.

The delta of the Colorado River was historically a very wet area that supported extensive cottonwood gallery forests with abundant beaver.

Paul Martin of the University of Arizona presented the case that big game hunters caused widespread extinctions within a few hundred years after their entry into North America from Siberia via the Bering Strait. However, the paleobotanic recon give no evidence of climatic changes severe enough to have resulted in the extinction of so many large animals over such a broad, diverse area. At the beginning of the Holocene, the last glacial/interglacial climatic shift, there are essentially no records of speciation or extinction in plants or small animals.

The region likely supported tropical deciduous forest from the Eocene to the early Miocene... Geology mocks our notion of permanence.

Mountain chains appear near coastlines for various geologic reasons, setting up orographic (mountain-induced) cooling of rising moist air masses to form coastal fog deserts and rain shadow deserts on the protected sides, such as coastal Baja California and the hyperdry Mohave Desert, respectively. Upland canyons, peidmonts, and mountaintops create new ecological niches, sites of adaptations and evolutionary change.

As climates and habitats change, plant and animal species either adapt, migrate to more favorable ground, or become extinct.

Ancient life affects later geologic and climatic conditions. Biologically produced gases (oxygen, carbon dioxide, methane, nitrous oxide) maintain a chemically reactive atmosphere that in turn influences rates of rock weathering, the nature of sedimentary deposits, and the content of gases in the atmosphere.

Desert soils, highly variable in their water-holding capability, salinity, and alkalinity determine the kinds of plants that will survive on them.

Topography is an important influence upon the unique climate of the Sonoran Desert, since topographic barriers direct, confine, or block moist air masses.

Volcanism and Regional Arching...
Intense heat rising into the crust was hot enough to entirely melt and soften portions of the lower continental crust into viscous fluid...

By about 12 million years ago, the entire substrata of Basin and Range country was involved with the expanded taffy-pull, stretching out some thirty to eighty percent more than its original width, while the brittle crusts above shattered into hundreds of long, thin segments.