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Perhaps the most spectacular feature of the Grand Canyon, its Redwall limestone cliff, stands about half way up the chasm and is practically vertical. Its average height is 550 feet-almost exactly that of the Washington Monument. Tough it is actually gray-blue limestone, the surface of the cliff has been stained to a sunset hue by iron salts washing out of the rocks. Above the Redwall come alternating layers of red sandstone and shale 1000 feet thick, then comes the next pale-blue layer. The topmost layers are a yellowish limestone. |
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