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List of Grand Canyon Rock Layers
What is Grand Canyon Stratigraphy?
Kaibab Formation
Toroweap Formation
Coconino Sandstone
Hermit Formation
Supai Group
Redwall Limestone
Tonto Group
Muav Limestone
Bright Angel Shale
Tapeats Sandstone
Vishnu Complex
Toroweap Formation
Permian Period, 275 Million Years Old, 250 Feet Thick.
A vegetated slope with a low cliff near its base.
Sandwiched between the Kaibab and Coconino cliffs lies an inconspicuous
sloping formation covered with trees. There is a moderate sized limestone
cliff 4/5 of the way down the slope. This slope-cliff-slope is the Toroweap
Formation.
Hikers first notice the formation when they descend to the first
pinkish mudstone layer. From the rim, look for these pink beds just below
the Kaibab cliff. The Toroweap has one of the most diverse rock varieties in
the Canyon: sandstone, mudstone, redbeds, gypsum, limestone, and dolomite.
The Toroweap was deposited near the shore
of a shallow sea whose incursion was interrupted by several temporary
retreats. The retreats left the varied sediments exposed to air in salty tidal
mudflats.
The Toroweap environment may have been analogous to
this scene from the Gulf of California. North and west of the Grand Canyon,
the Toroweap contains gypsum and salt deposits attesting to evaporation in a
shallow sea.
The Toroweap is not as
fossil-rich as the Kaibab Formation. The limestone cliff part way down,
called the Brady Canyon Member, represents the deepest water and contains
various shellfish
fossils. A more open marine fauna to the west,
characterized by brachiopods and crinoids, shows that the sea was deeper
there. In central Grand Canyon, and to the east, the fossils are mostly near-shore forms,
especially snails, scaphopods and clams. You can find these in trailside rocks at the Yavapai Point overlook.
This little story pretends that people were alive when the Kaibab Formation was laid down. But it was long before people. It was 275 million years ago. The purpose is to immerse ourselves in the time period--to imagine being there.
Our Tribe in Toroweap Time
For thousands of years our people have been the salt-gatherers of Pangaea. Our trade routes have broken eastward through the icy passes of Vermontia, the vast mountains that separate us from Europe. There is no Atlantic Ocean. Vermontia will one day erode down to its roots, and joggers will pass by in Central Park, New York. But we don't know that yet, and for now we have a land route to Europe and Asia.