Angular Unconformity, Grand Canyon, Arizona. Angular unconformities are ones in which the
overlying and underlying rocks dip at different angles. We can therefore infer that the underlying rocks
were tilted and eroded before the younger rocks were deposited. In the Grand Canyon, the Cambrian
Tapeats Sandstone is nearly flat-lying, and overlies tilted Proterozoic sedimentary rock. Elsewhere, it
overlies Proterozoic schist and granite as a nonconformity.


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