The

Middle Permian The Guadalupian is the second and middle series/ epoch of the Permian. The Guadalupian was preceded by the Cisuralian and followed by the Lopingian. It is named after the Guadalupe Mountains of New Mexico and Texas, and dates between 272.95 ...

Toroweap Formation is a thin, darker

geologic unit A stratigraphic unit is a volume of rock of identifiable origin and relative age range that is defined by the distinctive and dominant, easily mapped and recognizable petrographic, lithologic or paleontologic features (facies) that characterize ...

, between the brighter colored units of the

Kaibab Limestone The Kaibab Limestone is a resistant cliff-forming, Permian geologic formation that crops out across the U.S. states of northern Arizona, southern Utah, east central Nevada and southeast California. It is also known as the Kaibab Formation in Ar ...

above, and

Coconino Sandstone Coconino Sandstone is a geologic formation named after its exposure in Coconino County, Arizona. This formation spreads across the Colorado Plateau province of the United States, including northern Arizona, northwest Colorado, Nevada, and Utah. ...

below. It is a prominent unit in

Grand Canyon The Grand Canyon (, yuf-x-yav, Wi:kaʼi:la, , Southern Paiute language: Paxa’uipi, ) is a steep-sided canyon carved by the Colorado River in Arizona, United States. The Grand Canyon is long, up to wide and attains a depth of over a ...

Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a U.S. state, state in the Southwestern United States. It is the list of U.S. states and territories by area, 6th largest and the list of U.S. states and territories by population, 14 ...

, USA, found through sections of the South Rim, Grand Canyon, and the North Rim, of the

Kaibab Plateau The Kaibab Plateau is a plateau almost entirely in Coconino County, Arizona (but extending slightly north into Kane County, Utah) in the Southwestern United States. The high plain is also known as the Buckskin Mountain, Buckskin Plateau, and ...

; also the Kaibab's southeast extension to Cape Royal, the

Walhalla Plateau Walhalla is the German form of Old Norse ''Valhöll'', which is commonly anglicised as Valhalla. It may refer to: * Walhalla (memorial), a hall of fame in Donaustauf, Bavaria, Germany. Places Australia * Walhalla, Victoria, Australia * Elec ...

. The

Colorado River The Colorado River ( es, Río Colorado) is one of the principal rivers (along with the Rio Grande) in the Southwestern United States and northern Mexico. The river drains an expansive, arid watershed that encompasses parts of seven U.S. s ...

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 Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to its ...

. The Toroweap Formation is a darker unit of

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and dr ...

and

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especia ...

; also

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

. 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 The Permian Hermit Formation, also known as the Hermit Shale, is a nonresistant unit that is composed of slope-forming reddish brown siltstone, mudstone, and very fine-grained sandstone. Within the Grand Canyon region, the upper part of the H ...

is shown forming slopes, above the slope forming 'redbeds' of the

Supai Group The Supai Group is a slope-forming section of red bed deposits found in the Colorado Plateau. The group was laid down during the Pennsylvanian to Lower Permian. Cliff-forming interbeds of sandstone are noticeable throughout the group. The Supai ...

. 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 Walnut Canyon National Monument (Hopi: Wupatupqa) is a United States National Monument located about southeast of downtown Flagstaff, Arizona, near Interstate 40. The canyon rim elevation is ; the canyon's floor is 350 ft lower. A long lo ...

, about 70 mi southeast of the Grand Canyon, and east of

Flagstaff, Arizona Flagstaff ( ) is a city in, and the county seat of, Coconino County in northern Arizona, in the southwestern United States. In 2019, the city's estimated population was 75,038. Flagstaff's combined metropolitan area has an estimated population ...

Marine transgression A marine transgression is a geologic event during which sea level rises relative to the land and the shoreline moves toward higher ground, which results in flooding. Transgressions can be caused by the land sinking or by the ocean basins filling ...

, 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, with easternmost 'strand-lines' locating the shoreline, Toroweap west, and Coconino sand dunes or beach deposits, east.

Toroweap Overlook

Halfway through the Grand Canyon (north side of Colorado River), at Toroweap Valley, with Toroweap Lake (a playa lake), an outcrop, or point overlooks the West Grand Canyon section. It is the site of the Toroweap Fault. Nine miles to the west is the roughly parallel Hurricane Fault (of Hurricane Cliffs, of Arizona/Utah), the west fault, of the Uinkaret Mountains (

Mount Trumbull Wilderness The Mount Trumbull Wilderness is a 7,880 acre (31 km2) wilderness area located on the Uinkaret Plateau in the Arizona Strip. It is managed by the Bureau of Land Management. The Mount Trumbull Wilderness is north of Grand Canyon National ...

). An eastern fault section separates here, and goes north into Utah, passing the west side of the Kanab Plateau. The Toroweap Overlook lies above the erosion resistant Tapeats Sandstone, near its west terminus in

. Southeast, across the river The Esplanade-(a regional section) is created, upon the erosion resistant Esplanade Sandstone, a resistant member of the

, (a unit above the Tapeats, but occurs on both the downside block, and upside block in the south side of the canyon, Colorado River); (The Esplanade is just upstream, with the Toroweap Fault forming its west flank). The Toroweap Overlook was visited in the 1800s by original photographers of the Grand Canyon.

Geologic sequence

The Permian geologic sequence common in the Grand Canyon:Chronic, 1983. ''Roadside Geology of Arizona'', graphic: ''Stratigraphic section of Paleozoic formations of the Colorado Plateau'', p. 179. * 4-

* 3-Toroweap Formation * 2-

* 1B-

* 1A- Esplanade Sandstone (also considered upper unit of

, Pennsylvanian-Permian boundary) File:Grand Canyon National Park-Arizona1575.JPG, North Rim, Grand Canyon:
4-Permian formations:
-4-

-3-Toroweap Formation
-2-

-1-

-X-(upon Supai Group "redbeds") File:WalnutCanyonNorthWall.jpg, Toroweap Formation in Walnut Canyon, east of

Darker middle section is Toroweap: above: (3):

; below: (1):

(showing fossil dunes)-(note erosion of dunes compared to horizontal bedding of Kaibab Limestone)

References

Citations

General sources

* ''Arizona DeLorme Atlas & Gazetteer'', 5th Edition, c. 2002, 76 pages, pp. 23, 24, 31, 32. * ''Arizona Road & Recreation Atlas'', Benchmark Maps, 2nd Edition, c. 1998, pp. 28–29, 62–63. * Chronic, Halka. ''Roadside Geology of Arizona'', c. 1983, 23rd printing, Mountain Press Publishing Co. 322 pages. pp. 229–232. (''US 89A Marble Canyon – Fredonia''), pp. 179–180. (softcover, ) * Lucchitta, 2001. ''Hiking Arizona's Geology'', Ivo Lucchitta, c 2001, Mountaineers's Books. (softcover, )

External links