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Stop
4
Desertification
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Due to erosion,
the roots of this grass are now entirely exposed |
Prior to the introduction of domestic livestock, many piedmont slopes within
the Nature Park would have supported several species of grasses with scattered
shrubs. Grazing and drought reduced the amount of grass and its
capacity to hold soil in place.
Runoff water strips away small soil particles (sand, silt, clay) from the unprotected
soil and leaves behind the larger gravel that already existed in the soil.
Over time, this produces an erosion pavement of gravel that functions
like armor to protect the soil from further erosion. The fertile
topsoil that once supported grasses is now gone and nutrient-poor subsoil
layers are at or near the surface.
The white coating on the rocks is calcite, a mineral composed of calcium carbonate
(CaCO3); some people call this caliche. It is a chemical
material similar to the hard water deposits that are left around faucets
in your house. Calcite plugs the pores between sand and gravel,
making it "nature's concrete". Calcite forms beneath the
soil surface, giving soils of arid regions a whitish or gray color.
It has been accumulating in this soil for more than 250,000 years.
The presence of the white coating at or near the soil surface is evidence
of soil erosion.
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