Layers at Monument Valley

At Monument Valley, the upper cliff is sandstone, which once formed a continuous layer that has been almost totally eroded away, except in these two buttes and in adjacent areas not visible in this photograph. This sandstone was formed by ancient sand dunes. The red slopes below the cliff consist of more easily eroded mudrocks, which formed a continuous layer that is beneath and older than the sandstone. The mudrocks were deposited by rivers and in mud flats. Small layers are visible in the slope, and each of these represents an event, like a flood, or a change in the environment. The broad plateau surrounding the slopes is composed of another layer of sandstone, but one that is beneath the mudrocks.

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