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Bright Angel Shale

Cambrian Period, 510 Million Years Old, 325 Feet Thick
Forms the broad greenish slope below the Muav and Redwall

The Bright Angel Shale consists mostly of shaly green mudstones with lesser amounts of fine-grained dark sandstones. Most of the formation is a sediment-covered slope or platform (called the Tonto Platform) broken by low sandstone ledges. Fossils of the Bright Angel include 47 species of trilobites, inarticulate brachiopods, and primitive mollusks. These may be found in the green shales and the thin fine-grained sandstones. Tracks, trails, and burrows are also common.

Here is a close view of the upper Bright Angel Shale as seen along the Kaibab Trail. In the right foreground you can see the thin-bedded nature of the shale and its greenish color from the mineral glauconite. Glauconite is known only from ocean sediments, another indicator of a marine environment for the Bright Angel Shale.