| Toroweap Formation | |
|---|---|
| Stratigraphic range: Early Permian, | |
 Toroweap formation in Grand Canyon National Park | |
| Type | Geological formation |
| Underlies | Kaibab Limestone-(Permian), Grand Canyon, North Rim, (Kaibab Plateau), also South Rim, and elsewhere in Arizona, Utah, Nevada |
| Overlies | Coconino Sandstone |
| Thickness | 200 feet (61 m) approximate maximum |
| Lithology | |
| Primary | gypsum & shale,[1] also sandstone |
| Location | |
| Region | (southwest)-Colorado Plateau Northern Arizona, southeast Utah |
| Extent | Grand Canyon, North & South Rims, northeast Arizona, southeast Utah |
The Middle Permian Toroweap Formation is a thin, darker geologic unit, between the brighter colored units of the Kaibab Limestone above, and Coconino Sandstone below. It is a prominent unit in Grand Canyon, Arizona, USA, found through sections of the South Rim, Grand Canyon, and the North Rim, of the Kaibab Plateau; also the Kaibab's southeast extension to Cape Royal, the Walhalla Plateau. The Colorado River of the Grand Canyon makes its excursion from due-south to due-west around the Walhalla Plateau, as it enters the east end of the Grand Canyon's interior, Granite Gorge. The formation is also found in southeast Utah.
The Toroweap Formation is a darker unit of gypsum and shale;[1] also sandstone. In photos the cliff-forming Kaibab and Coconino units, show the more erodable Toroweap Formation slope-forming accumulations upon the underlying Coconino Sandstone; likewise below the Coconino, the softer Hermit Formation is shown forming slopes, above the slope forming 'redbeds' of the Supai Group. Close-up views of the Toroweap will show the resistant sandstone sub-units as erosion resistant sections.
Cliffs of the Toroweap Formation can be found in Walnut Canyon National Monument, about 70 mi[2] southeast of the Grand Canyon, and east of Flagstaff, Arizona.
Marine transgression, and continental wind-blown sand, laid down the three units of Kaibab, Toroweap, and Coconino. The oceanic sea came from the west, and receded and re-transgressed. The Coconino Sandstone being made of sand dunes, continental, means that near-shore Toroweap deposits, and off-shore Kaibab Limestone, can all have the same actual ages in different regions where they were deposited, (continental, near-shore, open sea). In Arizona, the Toroweap formation is found in two transgressions eastwards,[3] with easternmost 'strand-lines' locating the shoreline, Toroweap west, and Coconino sand dunes or beach deposits, east.
