The canyon's layers
Top to bottom
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KAIBAB FORMATION
AGE: 250 million years
(Permian Period, Paleozoic Era)
THICKNESS: 300 feet
COMPOSITION: Mostly limestone; some sandstone and shale.
NOTES: The Kaibab Formation combines with the two layers immediately below it to form the whitish cliffs at the top of the Grand Canyon. These sedimentary layers are the canyon's youngest, but they are still old enough to predate the dinosaurs.
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TOROWEAP FORMATION
AGE: 255 million years
(Permian Period, Paleozoic Era)
THICKNESS: 250 feet
COMPOSITION: Limestone and sandstone
NOTES: The Toroweap Formation's gentler slope accommodates tree growth, creating a green band between the whitish cliffs of the Kaibab Formation above and the Coconino sandstone below.
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COCONINO SANDSTONE
AGE: 260 million years
(Permian Period, Paleozoic Era)
THICKNESS: 325 feet
COMPOSITION: Quartz sandstone
NOTES: These huge white cliffs were formed by ancient sand dunes.
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HERMIT SHALE
(Permian Period, Paleozoic Era)
AGE: 265 million years
THICKNESS: 300 feet
COMPOSITION: Shale
NOTES: Shale is formed by silt or clay deposits.
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SUPAI GROUP
AGE: 285 million years
(Pennsylvanian Period, Paleozoic Era)
THICKNESS: 600 feet
COMPOSITION: Shale and sandstone
NOTES: The Supai actually is a combination of four separate formations. The top one, a sandstone layer, forms the Esplanade plateau in the western part of the Grand Canyon.
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REDWALL LIMESTONE
AGE: 335 million years
(Mississippian Period, Paleozoic Era)
THICKNESS: 500 feet
COMPOSITION: Limestone and dolomite
NOTES: The cliffs of the Redwall are actually gray rock stained red by runoff from the Supai above.
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TEMPLE BUTTE LIMESTONE
AGE: 350 million years
(Devonian Period, Paleozoic Era)
THICKNESS: 80 feet
COMPOSITION: Limestone
NOTES: This formation appears only intermittently in the eastern part of the canyon, but in the west it forms large and continuous cliffs.
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MUAV LIMESTONE
AGE: 515 million years
(Cambrian Period, Paleozoic Era)
THICKNESS: 400 feet
COMPOSITION: Mostly limestone; some sandstone and shale.
NOTES: A gap of 150 million years exists between the times the Muav Limestone and the canyon's next-youngest layer, the Temple Butte Limestone, were formed.
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BRIGHT ANGEL SHALE
AGE: 530 million years
(Cambrian Period, Paleozoic Era)
THICKNESS: 375 feet
COMPOSITION: Shale; some sandstone and limestone
NOTES: If you hike the canyon, you probably will walk many a mile on Bright Angel shale; it is the rock of the Tonto Plateau.
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TAPEATS SANDSTONE
AGE: 545 million years
(Cambrian Period, Paleozoic Era)
THICKNESS: 100 feet
COMPOSITION: Sandstone
NOTES: This is the last layer before the rocks of the Precambrian Era -- when life was a whole lot simpler.
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GRAND CANYON SUPERGROUP
AGE: 1.2 billion years (Precambrian Era)
THICKNESS: Varies; several hundred feet
COMPOSITION: Primarily sandstone
NOTES: The distinctive tilted strata of the Grand Canyon Supergroup appear only intermittently in the western part of the canyon. The Supergroup is a prominent feature, however, from Red Canyon eastward; in that part of the canyon its thickness is like that of the Vishnu schist in the west.
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VISHNU GROUP
AGE: 2 billion years (Precambrian Era)
THICKNESS: 800 to 1,500 feet
COMPOSITION: Metamorphic gneiss and schist, laced with bands of pink Zoroaster granite.
NOTES: This rock is about half as old as Earth itself.
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