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| The western end of Glen Canyon is located near Lees Ferry. The Colorado River canyon cuts through a large structural fold in the rock, called the Echo Cliffs Monocline, exposing shales of the Chinle Formation (stratigraphically beneath the sandstones of the Glen Canyon Group exposed upriver in Glen Canyon). The Chinle Formation consists of shale, mudstone and sandstone formed from muddy sediments deposited by river systems on a broad coastal plain in the late Triassic Period (roughly 220 to 230 million years ago). Fossil logs and stumps preserved in some of the Chinle beds show that humid tropical to subtropical conditions existed in the region when the sediments were deposited. |
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