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South Rim October 20, 2008 |
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| The fast flowing Colorado cut through the sedimentary rock quickly, sometimes more so, sometimes less, depending on the hardness of the rock layer. But within maybe a million and a half years, the river had eroded through all but the much harder Vishnu layer at the bottom. Since the Vishnu layer is much harder, progress became much slower, and so the riverbed flattened out, slowing the river and its cutting force further. It has slowly been grinding away at the Vishnu layer ever since. |
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