Chihuahuan Desert Nature Park
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Stop 4
Desertification

Due to erosion, the roots of this grass are now entirely exposed
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.

Caliche formed on a rock

Caliche formed on a rock

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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