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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