Desert Soils
parent materials
alluvial fans
sediments: sand, silt, clay
mountainous: rock types, slopes, and exposures
soil-forming environments
water
physical reactions
chemical reactions
wind-blown dust
life in the soil
soil layers: clay, colors, caliche
caliche: "nearly impenetrable, cemented layers, or petrocalcic horizons"
calcium carbonate accumulation

Clay-rich layers are called argillic horizons.

The weatering (oxidation) and accumulation of iron-bearing minerals contained in the soil produce this [red] color.

Soil and Desert Life, Joseph R. McAulliffe
Animals can profoundly affect characteristics of desert soils. The animals that dig, wiggle, tunnel, and burrow through desert soils range in size from microscopic mite and nematodes to badgers and coyotes. Their activities move soil around and cycle nutrients among the realms of "animal, vegetable, and mineral."

Soil mites play a variety of ecological roles.

In the warm deserts of the American Southwest, termites are perhaps the greatest earth-movers. Desert termites accomplish the same kind of ecological role as do earthworms in the soils of moister regions.

Subtle changes in [soil] permeability and texture affect how much precipitation is either absorbed by the soil or lost to runoff, and how deeply water infiltrates the soil.

Human Ecology in the Sonoran Desert, Thomas E. Sheridan...1922, Aldo Leopold

"For all we could tell, the Delta had lain forgotten since Hernando de Alarcon landed there in 1540. When we camped on the estuary which is said to have harbored his ships, we had not for weeks seen a man or a cow, an axe-cut or a fence. On the map the Delta was bisected by the river, but in fact the river was nowhere and everywhere, for he could not decide which of a hundred green lagoons offered the most pleasant and least speedy path to the Gulf. So he traveled them all and so did we. He divided and rejoined, he twisted and turned, he meandered in awesome jungles, he all but ran in circles, he dallied with lovely groves, he got lost and was glad of it, and so were we. For the last word in procrastination, go travel with a river reluctant to lose his freedom to the sea." Leopold, 1949, p141.

By the time Leopold wrote those words in the 1940's, he knew he was writing an elegy, not a paean. The river mighty enough to support a jungle in the desert had already lost its freedom, not to the Gulf of California into which it emptied, but to California farmers and the City of Los Angeles. Beginning in the 1890's, Anglo-American promoters and government engineers strove to break the Colorado to the new Western order. Their first attempts nearly triggered a geological catastrophe, when floods in 1905 sent the Colorado roiling down a canal with no headgate and turned the Salton Sink into the Salton Sea.