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-former, 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 Fo ...

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,

Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...

USA The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...

, 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. 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 it ...

. 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 drywal ...

and shale; 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 ...

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 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 loo ...

, about 70 mi southeast of the Grand Canyon, and east of Flagstaff, Arizona.

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 The Toroweap Fault of northwest Arizona and southwest Utah is part of a fault system of the west Grand Canyon region, Arizona, US; also the west perimeter regions of the Coconino and Colorado Plateaus. The Hurricane Fault originates at the T ...

. Nine miles to the west is the roughly parallel

Hurricane Fault The Hurricane Fault is an intracrustal seismic fault that runs along the boundary between the Colorado Plateau block and the Basin and Range geologic province of western North America. It is a 250-km-long, north-south striking, high-angle, down ...

(of

Hurricane Cliffs The Hurricane Cliffs of southwest Utah and northwest Arizona are a red, limestone geographic feature, sets of cliffs along the western, eroded edge of the Kaibab Limestone; the cliffs are about 135-mi (217 km) long,''Utah Atlas & Gazeteer ...

, 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 Kanab Plateau is a 45-mile (72 km) long plateau located at the north of the Grand Canyon in Arizona, United States. The plateau is adjacent west of the Kaibab Plateau of the North Rim, with a basin containing the Kanab Creek watershed in betw ...

. The

Toroweap Overlook Toroweap Overlook (also known as Tuweep Overlook or Toroweap Point) is a viewpoint within the Grand Canyon National Park in Arizona, United States. It is located in a remote area on the North Rim of the Grand Canyon, west of the North Rim Hea ...

lies above the erosion resistant

Tapeats Sandstone Except where underlain by the Sixtymile Formation, Cambrian Tapeats Sandstone is typically the lowest geologic unit, about thick, at its maximum, of the 5-member Tonto Group. It is famous for being the highly-resistant mostly-horizontal unit ...

, near its west terminus in Grand Canyon. Southeast, across the river The Esplanade-(a regional section) is created, upon the erosion resistant

Esplanade Sandstone The Lower Permian Esplanade Sandstone is a cliff-forming, resistant sandstone, dark red, geologic unit found in the Grand Canyon. The rock unit forms a resistant shelf in the west Grand Canyon, south side of the Colorado River, at the east of t ...

, a resistant member of the Supai Group, (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-

(also considered upper unit of Supai Group, 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 Flagstaff, Arizona
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