Tonto Group

Tonto Group
Tonto Group
Stratigraphic range: ; Cambrian,; 507–497 Ma PreꞒ Ꞓ O S D C P T J K Pg N
	Muav Limestone-(broader-based gray cliff supporting tall-reddish Redwall Limestone cliff) and Bright Angel Shale-(greenish & extensive slope-former), resting on Tapeats Sandstone-(short, dark vertical cliff on gorge rim) and the Tonto Platform, inner canyon, Granite Gorge (the two units are easily seen below the red-stained Redwall Limestone (~550 ft thick))
Type	Geologic group
Unit of	Sauk sequence
Sub-units	Frenchman Mountain Dolostone, Muav Limestone, Bright Angel Shale, Tapeats Sandstone, and Sixtymile Formation
Underlies	Redwall Limestone. ; (Locally underlies Temple Butte Formation that fills paleovalleys cut into unconformity separating Redwall Limestone from either Frenchman Mountain Dolostone or Muav Limestone.
Overlies	Vishnu Basement Rocks and Grand Canyon Supergroup
Thickness	1,250 feet (380 m)
Lithology
Primary	sandstone, conglomerate, siltstone, shale, limestone, and dolomite
Other	calcareous mudstone and glauconitic sandstone
Location
Region	Arizona-(northern) and, ; Nevada-(southern)
Country	United States-(Southwestern United States)
Type section
Named for	Tonto Creek or Tonto Basin,
Named by	G. K. Gilbert
Location	Backtail Canyon

Last updated June 17, 2023

The Tonto Group is a name for an assemblage of related sedimentary strata, collectively known by geologists as a Group , that comprises the basal sequence Paleozoic strata exposed in the sides of the Grand Canyon. As currently defined, the Tonto groups consists of the Sixtymile Formation, Tapeats Sandstone, Bright Angel Shale (or Formation), Muav Limestone (or Formation), and Frenchman Mountain Dolostone. Historically, it included only the Tapeats Sandstone, Bright Angel Shale, and Muav Limestone.^[1]^[2] Because these units are defined by lithology and three of them interfinger and intergrade laterally, they lack the simple layer cake geology as they are typically portrayed as having and geological mapping of them is complicated.^[5]^[6]

Nomenclature

In 1874 and 1875, G. K. Gilbert named the Tonto Group.^[7]^[3] Although it was mentioned that it outcropped in the Tonto Basin and the headwaters of Tonto Creek of south-central Arizona, he did not indicate which of these landforms, for which this group is named. Although the word tonto is translated as silly or foolish in Spanish, this place name for either Tonto Basin or Tonto Creek is derived from the Apache word, Koun’nde. This word means wild, rough people and refers to the indigenous Dilzhe’e Tonto Apache.^[8]^[9]

G. K. Gilbert also recognized that rocks similar to those found in the Tonto Basin are exposed near the bottom of the Grand Canyon and designated them also as the Tonto Group. From youngest to oldest, Gilbert subdivided the Tonto Group found in the Grand Canyon into the Marbled limestone (now subdivided into the Muav Limestone and Frenchman Dolostone); the Tonto shale (now the Bright Angel Shale); the Tonto sandstone (now the Tapeats Sandstone). However, he did not specify a specific type locality.^[3] Decades later, R. C. Rose proposed an exposure in Backtail Canyon for a type locality.^[4]

In 1914, L F. Noble^[10] officially redefined and renamed the formations comprising the Tonto Group. The Tonto sandstone was officially renamed the Tapeats Sandstone and the Tonto shale was officially renamed the Bright Angel Shale. The Marbled limestone was later officially renamed the Muav Limestone, which by Noble's definition consisted of an upper set of dolomite beds and a lower set of limestone beds.^[11]

Later in 1945, E. D. McKee and C. E. Resser^[12] subdivided the formations into a number of members in their recognition of the laterally gradation, time transgressive, and interfingering nature of the formations comprising the Tonto Group. In addition, they subdivided the Muav Limestone of Noble into undifferentiated dolomites, overlying an Muav Limestone composed entirely of the lower limestone strata. Furthermore, they removed the undifferentiated dolomites from the Tonto Group.^[12] Recently, the undifferentiated dolomites, now known as the Frenchman Mountain Dolostone, have been restore as a formation within the Tonto Group. In addition, along with the Frenchman Mountain Dolostone, the Sixtymile Formation is regarded to be part of the Tonto Group.^[1]^[2]

Throughout the majority of it extent, the Tonto Group lies unconformably on underlying Precambrian rocks forming the Great Unconformity. This contact is either an angular unconformity truncating tilted strata of the Grand Canyon Supergroup or either a nonconformity cut into the crystalline Vishnu Basement Rocks. The base of the Tonto Group consists of discontinuous beds of the Sixtymile Formation at Nankoweap Butte and within Awatubi and Sixtymile Canyons in the eastern Grand Canyon.^[1]^[2]

Description

As currently defined Tonto Group consists of the Sixtymile Formation, Tapeats Sandstone, Bright Angel Shale, Muav Limestone, and Frenchman Mountain Dolostone.^[1]^[2]

The Sixtymile Formation is a very thin accumulation of sandstone, siltstone, and breccia underlying the Tapeats Sandstone. It is exposed only atop Nankoweap Butte and within Awatubi and Sixtymile Canyons in the eastern Grand Canyon, Arizona. Sixtymile Formation is preserved only in a broad asymmetric fold, called the Chuar syncline. The maximum thickness of the Sixtymile Formation is about 60 meters (200 ft). The actual depositional thickness of the Sixtymile Formation is unknown owing to erosion prior to deposition of the Tapeats Sandstone. The Sixtymile Formation unconformably overlies the Chur Group. No fossils have been reported from the Sixtymile Formation.^[13]

In the Grand Canyon, the Tapeats Sandstone is a medium- to coarse-grained, thin-bedded, cliff-forming conglomeratic sandstone that weathers to a tan or reddish-brown. Its thickness varies from very thin or absent where deposited over prominent paleotopographic highs, as much as to 90 meters (300 ft) high. Typically, fine sandstone becomes common towards the top in its upper 12 to 15 meters (39 to 49 ft), which is part of a transition zone between it and the overlying Bright Angel Shale. The basal part of the Tapeats Sandstone is locally conglomeratic with beds of mudstone.^[14] Except where it overlies the Sixtymile Formation, the base of the Tapeats Sandstone is an unconformity underlying Precambrian rocks and is known as the Great Unconformity. In the eastern Grand Canyon, the Tapeats Sandstone uncomfortably overlies a hilly and weathered paleosurface underlain by the Grand Canyon Group and, in one structural basin, the Cambrian Sixtymile Formation. In the western Grand Canyon, the Tapeats Sandstone uncomfortably overlies a hilly and weathered paleosurface underlain by the Vishnu Basement Rocks^[1] The Tapeats Sandstone contains abundant invertebrate burrows and trails. But, body fossils, such as the fossils of brachiopods and trilobites are absent, except where it interfingers with the overlying Bright Angel Shale.^[2]^[14]

The Bright Angel Shale consists of green and red-brown, micaceous, thin-bedded shale, siltstone, and sandstone that weathers to a slope of the same colors. It is mostly composed of fissile shale (mudstone) and siltstone with some thicker beds of brown to tan sandstones and dolostones all of which are sometimes divided into numerous members. The Bright Angel Shale is about 57 to 150 meters (187 to 492 ft) thick. The thin-bedded shales and sandstones are often interbedded in cm-scale cycles. Sedimentary structures are abundant in the Bright Angel Shale and include current, oscillation, and interference ripples. The Bright Angel Shale has a complex gradational and interfingering relationship with the overlying Muav Limestone and underlying Tapeats Sandstone.^[2]^[14] The Bright Angel Shale is the most fossiliferous of the formations of the Tonto Group. It has yielded majority of the body fossils known from the Tonto Group and is particularly rich in ichnofossils. As a whole, trilobite and other body fossils are fragmentary and rare in Bright Angel Shale. However, individual fossil quarries in the Bright Angel Shale, when excavated, are just as productive as many other Cambrian formations in the Great Basin and Rocky Mountain regions. Finally, possible bryophyte-grade cryptospores have been recovered from the Bright Angel Shale.^[15]

The Muav Limestone consists of thin-bedded, gray, medium to fine-grained, mottled dolomite; coarse- to medium-grained, grayish-white, sandy dolomite; and fine-grained limestone. It also contains thin beds of shale and siltstone, and conglomerate. The Muav Limestone weathers to a dark gray or rusty-orange color and forms cliffs or small ledges. This formation varies between 45 and 254 meters (148 and 833 ft) in thickness. Its upper contact is a disconformity with the overlying Frenchman Mountain Dolostone.^[2]^[14] In the Muav Limestone, body fossils are infrequent and often poorly preseved. They include sponges, brachiopods, hyoliths, helcionelloids, trilobites, eocrinoids, and enigmatic invertebrates (Chancelloria, Scenella). Trilobites found in the Muav Limestone are of the same age as trilobites found in the Bright Angel Shale of eastern Grand canyon region, so it is likely not substantially younger. The trace fossils are common in the Muav Limestone and less abundant than the underlyingright Angel Shale. These trace fossils consist of invertebrate burrows and trails and Girvanella-like structures (oncolites).^[2]

The Frenchman Mountain Dolostone consists of white to dark gray, thin- to medium-bedded dolomite, which is separated by the underlying Muav Limestone by a disconformity throughout the Grand Canyon region. Its lower part contains shale partings that separate individual dolomite beds. The Frenchman Mountain Dolostone forms a series of ledges, cliffs, and slopes. Its thickness varies from 60 to 140 meters (200 to 460 ft). The only known fossils reported from the Frenchman Mountain Dolostone are invertebrate burrows and trails.^[1]^[2]

Tonto Platform

The Tonto Platform is a very prominent, wide bench that occurs near the bottom of the eastern Grand Canyon. The gentle slopes of the Tonto Platform were created by rapid backwearing^{[ clarification needed ]} of the Bright Angle Shale. Along its lower edge, the erosion resistant Tapeats Sandstone forms a cliff that marks the outer boundary of the Inner Gorge and the lower boundary of the Outer Canyon. Forming the upper edge of the Tonto Platform are alternating cliffs and steep slopes formed by Cambrian limestones and dolomites. The Tonto Trail is a mostly horizontal trail on the south side of Granite Gorge that lies upon the Tonto Platform.^[16]^[17]

View of Tower of Set peak and sub-unit cliff section from Tonto Trail, Granite Gorge, north of Mohave Point, Grand Canyon Village, South Rim.
The peak is behind and separated from a cliff unit (with small prominence), in front-(photo center, right, Tower of Set (peak) to its left).
Vertical erosion in cliff of Redwall Limestone, upon horizontal Muav Limestone cliff.^[18] The Tapeats Sandstone sits in foreground on Granite Gorge, and is seen as thinly-bedded. The slope-former above is the (dull-greenish)-Bright Angel Shale with thin, inter-bedding, as well as one resistant cliff unit. The Redwall Limestone cliff section in Grand Canyon is about 450 feet (137 m) thick.^[19]
close-up and far views of the Tonto Group formations.
Note in far view the cliff-run of the Tapeats Sandstone cliff below the (whitish)-greenish Bright Angel Shale-(often dull-greenish, but even yellowish in northeast Grand Canyon).

Related Research Articles

The geology of the Grand Canyon area includes one of the most complete and studied sequences of rock on Earth. The nearly 40 major sedimentary rock layers exposed in the Grand Canyon and in the Grand Canyon National Park area range in age from about 200 million to nearly 2 billion years old. Most were deposited in warm, shallow seas and near ancient, long-gone sea shores in western North America. Both marine and terrestrial sediments are represented, including lithified sand dunes from an extinct desert. There are at least 14 known unconformities in the geologic record found in the Grand Canyon.

Of the many unconformities (gaps) observed in geological strata, the term Great Unconformity is frequently applied to either the unconformity observed by James Hutton in 1787 at Siccar Point in Scotland, or that observed by John Wesley Powell in the Grand Canyon in 1869. Both instances are exceptional examples of where the contacts between sedimentary strata and either sedimentary or crystalline strata of greatly different ages, origins, and structure represent periods of geologic time sufficiently long to raise great mountains and then erode them away.

The Muav Limestone is a Cambrian geologic formation within the 5-member Tonto Group. It is a thin-bedded, gray, medium to fine-grained, mottled dolomite; coarse- to medium-grained, grayish-white, sandy dolomite and grayish-white, mottled, fine-grained limestone. It also contains beds of shale and intraformational conglomerate. The beds of the Muav Limestone are either structureless or exhibit horizontally laminations and cross-stratification. The Muav Limestone forms cliffs or small ledges that weather a dark gray or rusty-orange color. These cliffs or small ledges directly overlie the sloping surfaces of the Bright Angel Shale. The thickness of this formation decreases eastward from 250 feet (76 m) in the western Grand Canyon to 45 feet (14 m) in the eastern Grand Canyon. To the west in southern Nevada, its thickness increases to 830 feet (250 m) in the Frenchman Mountain region.

Except where underlain by the Sixtymile Formation, the Tapeats Sandstone is a Cambrian geologic formation that is the basal geologic unit of the Tonto Group. Typically, it is also the basal geologic formation of the Phanerozoic strata exposed in the Grand Canyon, Arizona, and parts of northern Arizona, central Arizona, southeast California, southern Nevada, and southeast Utah. The Tapeats Sandstone is about 230 feet (70 m) thick, at its maximum. The lower and middle sandstone beds of the Tapeats Sandstone are well-cemented, resistant to erosion, and form brownish, vertical cliffs that rise above the underlying Precambrian strata outcropping within Granite Gorge. They form the edge of the Tonto Platform. The upper beds of the Tapeats Sandstone form the surface of the Tonto Platform. The overlying soft shales and siltstones of the Bright Angel Shale underlie drab-greenish slopes that rise from the Tonto Platform to cliffs formed by limestones of the Muav Limestone and dolomites of the Frenchman Mountain Dolostone.

The Cardenas Basalt, also known as either the Cardenas Lava or Cardenas Lavas, is a rock formation that outcrops over an area of about 310 km² (120 mi²) in the eastern Grand Canyon, Coconino County, Arizona. The lower part of the Cardenas Basalt forms granular talus slopes. Its upper part forms nearly continuous low cliffs that are parallel to the general course of the Colorado River. The most complete, readily accessible, and easily studied exposure of the Cardenas Basalt lies in Basalt Canyon. This is also its type locality.

The Unkar Group is a sequence of strata of Proterozoic age that are subdivided into five geologic formations and exposed within the Grand Canyon, Arizona, Southwestern United States. The 5-unit Unkar Group is the basal member of the 8-member Grand Canyon Supergroup. The Unkar is about 1,600 to 2,200 m thick and composed, in ascending order, of the Bass Formation, Hakatai Shale, Shinumo Quartzite, Dox Formation, and Cardenas Basalt. Units 4 & 5 are found mostly in the eastern region of Grand Canyon. Units 1 through 3 are found in central Grand Canyon. The Unkar Group accumulated approximately between 1250 and 1104 Ma. In ascending order, the Unkar Group is overlain by the Nankoweap Formation, about 113 to 150 m thick; the Chuar Group, about 1,900 m (6,200 ft) thick; and the Sixtymile Formation, about 60 m (200 ft) thick. These are all of the units of the Grand Canyon Supergroup. The Unkar Group makes up approximately half of the thickness of the 8-unit Supergroup.

The Neoproterozoic Nankoweap Formation, is a thin sequence of distinctive red beds that consist of reddish brown and tan sandstones and subordinate siltstones and mudrocks that unconformably overlie basaltic lava flows of the Cardenas Basalt of the Unkar Group and underlie the sedimentary strata of the Galeros Formation of the Chuar Group. The Nankoweap Formation is slightly more than 100 m in thickness. It is informally subdivided into informal lower and upper members that are separated and enclosed by unconformities. Its lower (ferruginous) member is 0 to 15 m thick. The Grand Canyon Supergroup, of which the Nankoweap Formation is part, unconformably overlies deeply eroded granites, gneisses, pegmatites, and schists that comprise Vishnu Basement Rocks.

Temple Butte, in the Grand Canyon, Arizona, US is a prominence below the East Rim. The butte lies on the west bank of the south-flowing Colorado River. The outfall from the Little Colorado River, draining from the Painted Desert to the east and southeast, is about two miles upstream.

Isis Temple is a prominence in the Grand Canyon, Arizona, Southwestern United States. It is located below the North Rim and adjacent to the Granite Gorge along the Colorado River. The Trinity Creek and canyon flow due south at its west border; its north, and northeast border/flank is formed by Phantom Creek and canyon, a west tributary of Bright Angel Creek; the creeks intersect about 3 mi (4.8 km) southeast, and 1.0 mi (1.6 km) north of Granite Gorge. The Isis Temple prominence, is only about 202 ft (62 m) lower than Grand Canyon Village, the main public center on Grand Canyon’s South Rim.

The Grand Canyon Supergroup is a Mesoproterozoic to a Neoproterozoic sequence of sedimentary strata, partially exposed in the eastern Grand Canyon of Arizona. This group comprises the Unkar Group, Nankoweap Formation, Chuar Group and the Sixtymile Formation, which overlie Vishnu Basement Rocks. Several notable landmarks of the Grand Canyon, such as the Isis Temple and Cheops Pyramid, and the Apollo Temple, are surface manifestations of the Grand Canyon Supergroup.

The Hakatai Shale is a Mesoproterozoic rock formation with important exposures in the Grand Canyon, Coconino County, Arizona. It consists of colorful strata that exhibit colors varying from purple to red to brilliant orange. These colors are the result of the oxidation of iron-bearing minerals in the Hakatai Shale. It consists of lower and middle members that consist of bright-red, slope-forming, highly fractured, argillaceous mudstones and shale and an upper member composed of purple and red, cliff-forming, medium-grained sandstone. Its thickness, which apparently increases eastwards, varies from 137 to 300 m. In general, the Hakatai Shale and associated strata of the Unkar Group rocks dip northeast (10–30°) toward normal faults that dip 60° or more toward the southwest. This can be seen at the Palisades fault in the eastern part of the main Unkar Group outcrop area. In addition, thick, prominent, and dark-colored basaltic sills and dikes cut across the purple to red to brilliant orange strata of the Hakatai Shale.

The Bass Formation, also known as the Bass Limestone, is a Mesoproterozoic rock formation that outcrops in the eastern Grand Canyon, Coconino County, Arizona. The Bass Formation erodes as either cliffs or stair-stepped cliffs. In the case of the stair-stepped topography, resistant dolomite layers form risers and argillite layers form steep treads. In general, the Bass Formation in the Grand Canyon region and associated strata of the Unkar Group-rocks dip northeast (10°–30°) toward normal faults that dip 60+° toward the southwest. This can be seen at the Palisades fault in the eastern part of the main Unkar Group outcrop area. In addition, thick, prominent, and dark-colored basaltic sills intrude across the Bass Formation.

The Shinumo Quartzite also known as the Shinumo Sandstone, is a Mesoproterozoic rock formation, which outcrops in the eastern Grand Canyon, Coconino County, Arizona,. It is the 3rd member of the 5-unit Unkar Group. The Shinumo Quartzite consists of a series of massive, cliff-forming sandstones and sedimentary quartzites. Its cliffs contrast sharply with the stair-stepped topography of typically brightly-colored strata of the underlying slope-forming Hakatai Shale. Overlying the Shinumo, dark green to black, fissile, slope-forming shales of the Dox Formation create a well-defined notch. It and other formations of the Unkar Group occur as isolated fault-bound remnants along the main stem of the Colorado River and its tributaries in Grand Canyon.

Typically, the Shinumo Quartzite and associated strata of the Unkar Group dip northeast (10°–30°) toward normal faults that dip 60+° toward the southwest. This can be seen at the Palisades fault in the eastern part of the main Unkar Group outcrop area.

The Dox Formation, also known as the Dox Sandstone, is a Mesoproterozoic rock formation that outcrops in the eastern Grand Canyon, Coconino County, Arizona. The strata of the Dox Formation, except for some more resistant sandstone beds, are relatively susceptible to erosion and weathering. The lower member of the Dox Formation consists of silty-sandstone and sandstone, and some interbedded argillaceous beds, that form stair-stepped, cliff-slope topography. The bulk of the Dox Formation typically forms rounded and sloping hill topography that occupies an unusually broad section of the canyon.

The Bright Angel Shale is one of five geological formations that comprise the Cambrian Tonto Group. It and the other formations of the Tonto Group outcrop in the Grand Canyon, Arizona, and parts of northern Arizona, central Arizona, southeast California, southern Nevada, and southeast Utah. The Bright Angel Shale consists of locally fossiliferous, green and red-brown, micaceous, fissile shale (mudstone) and siltstone with local, thicker beds of brown to tan sandstone and limestone. It ranges in thickness from 57 to 450 feet. Typically, its thin-bedded shales and sandstones are interbedded in cm-scale cycles. They also exhibit abundant sedimentary structures that include current, oscillation, and interference ripples. The Bright Angel Shale also gradually grades downward into the underlying Tapeats Sandstone. It also complexly interfingers with the overlying Muav Limestone. These chracters make defining the upper and lower contacts of the Bright Angel Shale often difficult to define. Typically, its thin-bedded shales and sandstones erode into green and red-brown slopes that rise from the Tonto Platform up to cliffs formed by limestones of the overlying Muav Limestone and dolomites of the Frenchman Mountain Dolostone.

The Redwall Limestone is a resistant cliff-forming unit of Mississippian age that forms prominent, red-stained cliffs in the Grand Canyon, ranging in height from 500 feet (150 m) to 800 feet (240 m).

The Sixtymile Formation is a very thin accumulation of sandstone, siltstone, and breccia underlying the Tapeats Sandstone that is exposed in only four places in the Chuar Valley. These exposures occur atop Nankoweap Butte and within Awatubi and Sixtymile Canyons in the eastern Grand Canyon, Arizona. The maximum preserved thickness of the Sixtymile Formation is about 60 meters (200 ft). The actual depositional thickness of the Sixtymile Formation is unknown owing to erosion prior to deposition of the Tapeats Sandstone.

The Devonian Temple Butte Formation, also called Temple Butte Limestone, outcrops through most of the Grand Canyon of Arizona, USA; it also occurs in southeast Nevada. Within the eastern Grand Canyon, it consists of thin, discontinuous and relatively inconspicuous lenses that fill paleovalleys cut into the underlying Muav Limestone. Within these paleovalleys, it at most, is only about 100 feet (30 m) thick at its maximum. Within the central and western Grand Canyon, the exposures are continuous. However, they tend to merge with cliffs of the much thicker and overlying Redwall Limestone.

Zoroaster Temple is a 7,123-foot-elevation (2,171-meter) summit located in the Grand Canyon, in Coconino County of Arizona, USA. It is situated 5.5 miles (8.9 km) northeast of the Yavapai Point overlook on the canyon's South Rim, from which it can be seen towering over 4,600 feet above the Colorado River and Granite Gorge. Its nearest higher neighbor is Brahma Temple, less than one mile to the north-northeast. Zoroaster Temple is named for Zoroaster, an ancient Iranian prophet. This name was used by George Wharton James and Clarence Dutton. Dutton began the tradition of naming geographical features in the Grand Canyon after mythological deities. This geographical feature's name was officially adopted in 1906 by the U.S. Board on Geographic Names.

The Frenchman Mountain Dolostone is the uppermost and youngest of five Cambrian geologic formations that comprise the Tonto Group. It consists of beds of mottled white to gray dolomite often separated by thin seams of shale, especially in its lower part. In the Grand Canyon, this formation forms vertical cliffs that thicken westward between the top of the Muav Limestone and the base of either the Devonian Temple Butte Formation or Mississippian Redwall Limestone. Because of unidentified trace fossils and lack of datable body fossils, the Frenchman Mountain Dolostone exact age is uncertain. Within the Grand Canyon, it thickness varies betweeen 200 to 450 feet. West into the Lake Mead region, it thickens consderably and is 1,217 feet (371 m) thick at Frenchman Mountain near Las Vegas, Nevada.

References

1 2 3 4 5 6 7 8 9 Karlstrom, K.E., Mohr, M.T., Schmitz, M.D., Sundberg, F.A., Rowland, S.M., Blakey, R., Foster, J.R., Crossey, L.J., Dehler, C.M. and Hagadorn, J.W., 2020. Redefining the Tonto Group of Grand Canyon and recalibrating the Cambrian time scale. Geology, 48(5), pp. 425–430.
1 2 3 4 5 6 7 8 9 10 11 Connors, T.B., Tweet, J.S., and Santucci, V.L., 2020. Stratigraphy of Grand Canyon National Park. In: Santucci, V.L., Tweet, J.S., ed., pp. 54–74, Grand Canyon National Park: Centennial Paleontological Resource Inventory (Non-sensitive Version) . Natural Resource Report NPS/GRCA/NRR—2020/2103. National Park Service, Fort Collins, Colorado, 603 pp.
1 2 3 4 Gilbert, G.K., 1875. Report upon the geology of portions of Nevada, Utah, California, and Arizona, Chapter 6. In Wheeler, G.M., ed., pp. 17–187, Report on the Geographical and Geological Explorations and Surveys West of the One Hundredth Meridian, vol. 3. U.S. Geological and Geographical Survey, Publication of the Wheeler Survey, Washington, D.C., 681 pp.
1 2 Rose, E.C., 2011. Modification of the nomenclature and a revised depositional model for the Cambrian Tonto Group of the Grand Canyon, Arizona. in Hollingsworth, J.S., Sundberg, F.A., and Foster, J.R., ed., pp. 77–98, 303, Cambrian Stratigraphy and Paleontology of Northern Arizona and Southern Nevada. Museum of Northern Arizona Bulletin 67.
↑ Beus, S.S. and Billingsley, G.H., 1989. Paleozoic strata of the Grand Canyon, Arizona. in Elston, D.P., Billingsley, G.H., and Young, R.A., ed., pp. 122–127, Geology of Grand Canyon, northern Arizona (with Colorado River guides): Lees Ferry to Pierce Ferry, Arizona. P. M. Hanshaw. Field trips for the 28th International Geological Congress. American Geophysical Union, Washington, D.C.
↑ Huntoon, P.W., 1989. Cambrian Stratigraphic Nomenclature, Grand Canyon, Arizona‐Mappers Nightmare. in Elston, D.P., Billingsley, G.H., and Young, R.A., ed., pp. 128–130, Geology of Grand Canyon, northern Arizona (with Colorado River guides): Lees Ferry to Pierce Ferry, Arizona. P. M. Hanshaw. Field trips for the 28th International Geological Congress. American Geophysical Union, Washington, D.C.
↑ Gilbert, G.K., 1874. On the age of the Tonto sandstone (Abst.). Bulletin of the Philosophical Society of Washington, 1, p. 109.
↑ White Mountain Apache Tribe, 1998. Western Apache-English Dictionary: A Community-Generated Bilingual Dictionary. Tempe, Arizona, Arizona State University, Bilingual Review Press, 485 p.
↑ Atchison, C.L., Parker, W.G., Riggs, N.R., Semken, S., and Whitmeyer, S.J., 2019, Accessibility and inclusion in the field: A field guide for central Arizona and Petrified Forest National Park, in Pearthree, P.A., ed., pp. 39–60, Geologic Excursions in Southwestern North America: Geological Society of America Field Guide 55.
↑ Noble, L.F., 1914. The Shinumo quadrangle, Grand Canyon district, Arizona.U.S. Geological Survey Bulletin. 549. doi : 10.3133/B549. ISSN 0083-1093.
↑ Noble, L.F., 1922. A section of the Paleozoic formations of the Grand Canyon at the Bass Trail. U.S. Geological Survey Bulletin. 131-B, pp. 23–73
1 2 McKee, E.D., and Resser, C.E., 1945, Cambrian history of ;the Grand Canyon region. Carnegie Institution of Washington Publication 563, 168 pp.
↑ Dehler, C.M., Porter, S.M., and Timmons, J.M., 2012. The Neoproterozoic Earth system revealed from the Chuar Group of Grand Canyon, in Timmons, J.M., and Karlstrom, K.E., eds. Grand Canyon Geology: Two Billion Years of Earth's History. Special Paper no. 489. Geological Society of America, Boulder, Colorado. pp. 49–72.
1 2 3 4 Middleton, L.T. and Elliott, D.K., 2003. Tonto Group, in Beus, S. S., and Morales, M., eds. Grand Canyon geology Museum of Northern Arizona Press, Flagstaff, Arizona. pp. 90–106.
↑ Foster, R.J., 2011. Trilobites and other fauna from two quarries in the Bright Angel Shale (Middle Cambrian, Series 3; Delamaran), Grand Canyon National Park, Arizona. in Hollingsworth, J.S., Sundberg, F.A. & Foster, J.R., eds. Cambrian Stratigraphy and Paleontology of Northern Arizona and Southern Nevada.Museum of Northern Arizona Bulletin, 67:99–120.
↑ Maxson, J.H., 1946. Relationship of Scenery to Geology in the Grand Canyon. Engineering and Science, 9(3), pp. 4–13.
↑ Dexter, L.R., 2009. Grand Canyon: the puzzle of the Colorado River. in Migoń , P., ed., pp. 49–58, Geomorphological landscapes of the world. Springer, Dordrecht.
↑ Lucchitta, I. (2001) Hiking Arizona's Geology, Mountaineers's Books, Seattle, Washington. ISBN 0-89886-730-4) pp. 62–68, Kaibab Trail, pp. 66–67, photo and Fig. 10, View to the northwest from the top of the Redwall Limestone along the (S.) Kaibab Trail. The sketch identifies the geologic units visible from here.
↑ Chronic, H (2001) Roadside Geology of Arizona. The Mountaineers Books, Seattle, Washington. (softcover, ISBN 978-0-87842-147-3) p. 179.

External links

Mathis, A., and C. Bowman (2007) The Grand Age of Rocks: The Numeric Ages for Rocks Exposed within Grand Canyon, Grand Canyon National Park, Arizona, National Park Service, Grand Canyon National Park, Arizona.
Rowland, S. (nda) Frenchman Mountain Great Unconformity site. Department of Geoscience, University of Nevada, Las Vegas, Nevada.
Share, J. (2102a) The Great Unconformity of the Grand Canyon and the Late Proterozoic-Cambrian Time Interval: Part I – Defining It.
Share, J. (2102a) The Great Unconformity and the Late Proterozoic-Cambrian Time Interval: Part II – The Rifting of Rodinia and the "Snowball Earth" Glaciations That Followed.
Timmons, M. K. Karlstrom, and C. Dehler (1999) Grand Canyon Supergroup Six Unconformities Make One Great Unconformity A Record of Supercontinent Assembly and Disassembly. Boatman's Quarterly Review. vol. 12, no. 1, pp. 29–32.
Timmons, S. S. (2003) Learning to Read the Pages of a Book (Grand Canyon Geology Training Manual), National Park Service, Grand Canyon National Park, Arizona.

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[KarlstromOther2020a-1] 1 2 3 4 5 6 7 8 9 Karlstrom, K.E., Mohr, M.T., Schmitz, M.D., Sundberg, F.A., Rowland, S.M., Blakey, R., Foster, J.R., Crossey, L.J., Dehler, C.M. and Hagadorn, J.W., 2020. Redefining the Tonto Group of Grand Canyon and recalibrating the Cambrian time scale. Geology, 48(5), pp. 425–430.

[ConnorsOthers2020a-2] 1 2 3 4 5 6 7 8 9 10 11 Connors, T.B., Tweet, J.S., and Santucci, V.L., 2020. Stratigraphy of Grand Canyon National Park. In: Santucci, V.L., Tweet, J.S., ed., pp. 54–74, Grand Canyon National Park: Centennial Paleontological Resource Inventory (Non-sensitive Version) . Natural Resource Report NPS/GRCA/NRR—2020/2103. National Park Service, Fort Collins, Colorado, 603 pp.

[Gilbert1875a-3] 1 2 3 4 Gilbert, G.K., 1875. Report upon the geology of portions of Nevada, Utah, California, and Arizona, Chapter 6. In Wheeler, G.M., ed., pp. 17–187, Report on the Geographical and Geological Explorations and Surveys West of the One Hundredth Meridian, vol. 3. U.S. Geological and Geographical Survey, Publication of the Wheeler Survey, Washington, D.C., 681 pp.

[Rose2011a-4] 1 2 Rose, E.C., 2011. Modification of the nomenclature and a revised depositional model for the Cambrian Tonto Group of the Grand Canyon, Arizona. in Hollingsworth, J.S., Sundberg, F.A., and Foster, J.R., ed., pp. 77–98, 303, Cambrian Stratigraphy and Paleontology of Northern Arizona and Southern Nevada. Museum of Northern Arizona Bulletin 67.

[BeusOthers1989a-5] Beus, S.S. and Billingsley, G.H., 1989. Paleozoic strata of the Grand Canyon, Arizona. in Elston, D.P., Billingsley, G.H., and Young, R.A., ed., pp. 122–127, Geology of Grand Canyon, northern Arizona (with Colorado River guides): Lees Ferry to Pierce Ferry, Arizona. P. M. Hanshaw. Field trips for the 28th International Geological Congress. American Geophysical Union, Washington, D.C.

[Huntoon1989a-6] Huntoon, P.W., 1989. Cambrian Stratigraphic Nomenclature, Grand Canyon, Arizona‐Mappers Nightmare. in Elston, D.P., Billingsley, G.H., and Young, R.A., ed., pp. 128–130, Geology of Grand Canyon, northern Arizona (with Colorado River guides): Lees Ferry to Pierce Ferry, Arizona. P. M. Hanshaw. Field trips for the 28th International Geological Congress. American Geophysical Union, Washington, D.C.

[Gilbert1874a-7] Gilbert, G.K., 1874. On the age of the Tonto sandstone (Abst.). Bulletin of the Philosophical Society of Washington, 1, p. 109.

[WhiteMountainApacheTribe1998a-8] White Mountain Apache Tribe, 1998. Western Apache-English Dictionary: A Community-Generated Bilingual Dictionary. Tempe, Arizona, Arizona State University, Bilingual Review Press, 485 p.

[Atchison2019a-9] Atchison, C.L., Parker, W.G., Riggs, N.R., Semken, S., and Whitmeyer, S.J., 2019, Accessibility and inclusion in the field: A field guide for central Arizona and Petrified Forest National Park, in Pearthree, P.A., ed., pp. 39–60, Geologic Excursions in Southwestern North America: Geological Society of America Field Guide 55.

[Noble1914a-10] Noble, L.F., 1914. The Shinumo quadrangle, Grand Canyon district, Arizona.U.S. Geological Survey Bulletin. 549. doi : 10.3133/B549. ISSN 0083-1093.

[Noble1922a-11] Noble, L.F., 1922. A section of the Paleozoic formations of the Grand Canyon at the Bass Trail. U.S. Geological Survey Bulletin. 131-B, pp. 23–73

[McKeeOthers1945a-12] 1 2 McKee, E.D., and Resser, C.E., 1945, Cambrian history of ;the Grand Canyon region. Carnegie Institution of Washington Publication 563, 168 pp.

[Dehler2012a-13] Dehler, C.M., Porter, S.M., and Timmons, J.M., 2012. The Neoproterozoic Earth system revealed from the Chuar Group of Grand Canyon, in Timmons, J.M., and Karlstrom, K.E., eds. Grand Canyon Geology: Two Billion Years of Earth's History. Special Paper no. 489. Geological Society of America, Boulder, Colorado. pp. 49–72.

[MiddletonOthers2003a-14] 1 2 3 4 Middleton, L.T. and Elliott, D.K., 2003. Tonto Group, in Beus, S. S., and Morales, M., eds. Grand Canyon geology Museum of Northern Arizona Press, Flagstaff, Arizona. pp. 90–106.

[Foster2011a-15] Foster, R.J., 2011. Trilobites and other fauna from two quarries in the Bright Angel Shale (Middle Cambrian, Series 3; Delamaran), Grand Canyon National Park, Arizona. in Hollingsworth, J.S., Sundberg, F.A. & Foster, J.R., eds. Cambrian Stratigraphy and Paleontology of Northern Arizona and Southern Nevada.Museum of Northern Arizona Bulletin, 67:99–120.

[Maxson1946a-16] Maxson, J.H., 1946. Relationship of Scenery to Geology in the Grand Canyon. Engineering and Science, 9(3), pp. 4–13.

[Dexter2009a-17] Dexter, L.R., 2009. Grand Canyon: the puzzle of the Colorado River. in Migoń , P., ed., pp. 49–58, Geomorphological landscapes of the world. Springer, Dordrecht.

[Lucchitta2001a-18] Lucchitta, I. (2001) Hiking Arizona's Geology, Mountaineers's Books, Seattle, Washington. ISBN 0-89886-730-4) pp. 62–68, Kaibab Trail, pp. 66–67, photo and Fig. 10, View to the northwest from the top of the Redwall Limestone along the (S.) Kaibab Trail. The sketch identifies the geologic units visible from here.

[Chronic2001a-19] Chronic, H (2001) Roadside Geology of Arizona. The Mountaineers Books, Seattle, Washington. (softcover, ISBN 978-0-87842-147-3) p. 179.

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