Geology and Soils in Deserts of the Southwestern United States - Design with the Desert: Conservation and Sustainable Development - page 47

FIGURE 2.8
Dunes and dune fields, such as the Kelso Dunes of California, pictured here, can develop wherever there
is constant wind and a source of sediments movable by the wind. Vegetation is in the process of stabilizing
this dune, but sand ripples in the foreground indicate that motion of particles by saltation is still occurring.
(Courtesy of W.L. Stefanov.)
beds (playas). If enough sediment is available and steady winds are present, mobile dunes
can migrate (in some cases quite rapidly) over the landscape. Dunes can lose mobility or
become “anchored” if vegetation or soil forms following climate change, the dune becomes
cemented by carbonate or clay-rich sediments, or if sediment is no longer available to feed
continued dune formation.
2.8 Desert Soils
The unconsolidated products of weathering can be considered simply as sediment on its
way to eventual consolidation as rock, but this would be a narrow view that diminishes
the role of biological processes in the formation of a material that serves as the interface
between rocks, minerals, and living things—soil. Soil is a necessary component of agri-
culture and, by extension, urban civilization as we know it today. Soil is defined in vari-
ous ways by different user groups, but we will define it as the collection of natural bodies
occupying parts of the earth's surface that support plants and that have properties due to
the integrated effect of climate and living matter action upon parent material, as condi-
tioned by relief, over periods of time. This statement incorporates elements common to
many definitions of soil, such as unconsolidated mineral matter at the surface of the earth,
and the natural medium for plant growth. Soils are considered to be a product of the five
soil-forming factors of climate, parent material, organisms, relief, and time. 16 Young soils
in deserts tend to be “immature” in that they contain many primary rock minerals that
have not chemically weathered into mineral types that are more stable at surface condi-
tions. These soils also tend to have low content of organic carbon due primarily to the low
above- and below-ground biomass of plants. Eolian (or wind-driven) processes are impor-
tant in desert soil formation (see Chapter 1), but in-place formation of soil from weathering
of bedrock is also important.