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Coconino Sandstone
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From Wikipedia
Hermit, Coconino, Toroweap, and Kaibab
Like the Supai Group below it, the Hermit Shale was deposited in a swampy environment (see 6a in figure 1). The alternating thin-bedded iron oxide, mud and silt were deposited via freshwater streams in a semiarid environment an average of 265 million years ago. Fossils of winged insects, cone-bearing plants, and ferns are found in this formation as well as tracks of amphibians and reptiles. It is a soft, deep red shale and mudstone slope-former in the canyon that is 160 to 175 feet (49 to 53 m) thick. Slope development will periodically undermine the formations above and car- to house-sized blocks of that rock will cascade down onto the Tonto Platform. An unconformity marks the top of this formation.

The Coconino Sandstone formed as the area dried out and sand dunes made of pure quartz sand invaded a growing desert some 260 million years ago (see 6b in figure 1). Today, it is a 375 to 650 ft (115 to 200 m) thick golden white to cream-colored cliff-former near the canyon's rim. Eolian (wind-created) cross bedding patterns of the frosted, well-sorted and rounded sand can be seen in its fossilized sand dunes. Also fossilized are arthropod and early reptile tracks along with some burrows. An unconformity marks the top of this formation.

Next in the geologic column is the Toroweap Formation, 200 to 250 feet (60 to 75 m) thick (see 6c in figure 1). It consists of red and yellow sandstone and shaly gray limestone interbedded with gypsum that were deposited in a warm, shallow sea as its shoreline transgressed (invaded) and regressed (retreated) over the land (average age of the rock is about 250 million years). In modern times it is a ledge- and cliff-former that contains fossils of brachiopods, corals, and mollusks along with other animals and various terrestrial plants. The Toroweap is divided into the following three members:

Seligman: Slope-forming yellowish to reddish sandstone and siltstone.
Brady Canyon: Cliff-forming gray limestone with some chert.
Wood Ranch: Slope-forming pale red and gray siltstone and dolomitic sandstone.
An unconformity marks the top of this formation.

One of the highest, and therefore youngest, formations seen in the Grand Canyon area is the massive Kaibab Limestone, 250 to 350 feet (80 to 110 m) thick (see 6d in figure 1). A prominent ledgy cliff-former, the Kaibab Limestone was laid down in middle Permian time an average of about 225 million years ago in the deeper parts of the same advancing warm, shallow sea that deposited the underlying Toroweap Formation. The Kaibab is typically made of sandy limestone sitting on top of a layer of sandstone, but in some places sandstone and shale are near or at the top.[7] This is the cream to grayish-white rock that park visitors stand on while enjoying the spectacular vistas of the canyon from both rims (some call it "Grand Canyon's bathtub ring" due to its appearance). It is also the surface rock covering much of the Kaibab Plateau just north of the canyon and the Coconino Plateau immediately south. Shark teeth have been found in this formation as well abundant fossils of marine invertebrates such as brachiopods, corals, mollusks, sea lilies, and worms. An unconformity marks the top of this formation.

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