Unkar Delta at Mile 73The layers of brick red sandstone, siltstone, and mudstone of the Dox formation deposited a billion years ago, erode easily, giving the landscape an open, rolling character very different that the narrow, limestone walled canyon upstream, both in lithology and color, fully fitting Van Dyke’s description of “raspberry-red color, tempered with a what-not of mauve, heliotrope, and violet.” Sediments flowing in from the west formed deltas, floodplains, and tidal flats, which indurated into these fine-grained sedimentary rocks thinly laid deposits of a restful sea, lined with shadows as precise as the staves of a musical score, ribboned layers, an elegant alteration of quiet siltings and delicious lappings, crinkled water compressed, solidified, lithified.
Ann Zwinger, Downcanyon: A Naturalist Explores the Colorado River through the Grand Canyon
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