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Some of the soils of the Southwest are notably susceptible to erosion, especially under two effects that can be, but are not always or necessarily, related: grazing and climatic change. There is much discussion, and uncertainty, as to just what causes dramatic incision of rivers, like the Rio Puerco, here. Some argue that it is the several hundred year history of livestock grazing, which has depleted the vegetative cover. Others counter that it could as easily be climatic change, for which livestock can hardly be held accountable. No doubt there is a synergy between the two, but so is there controversy.
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