The San Rafael Group is a

geologic group In geology, a group is a lithostratigraphic unit consisting of a series of related formations that have been classified together to form a group. Formations are the fundamental unit of stratigraphy. Groups may sometimes be combined into superg ...

or collection of related rock

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondary ...

s that is spread across the

U.S. state In the United States, a state is a constituent political entity, of which there are 50. Bound together in a political union, each state holds governmental jurisdiction over a separate and defined geographic territory where it shares its so ...

s of

New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...

Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...

Utah Utah is a landlocked state in the Mountain states, Mountain West subregion of the Western United States. It is one of the Four Corners states, sharing a border with Arizona, Colorado, and New Mexico. It also borders Wyoming to the northea ...

and

Colorado Colorado is a U.S. state, state in the Western United States. It is one of the Mountain states, sharing the Four Corners region with Arizona, New Mexico, and Utah. It is also bordered by Wyoming to the north, Nebraska to the northeast, Kansas ...

. As part of the

Colorado Plateau The Colorado Plateau is a physiographic and desert region of the Intermontane Plateaus, roughly centered on the Four Corners region of the Southwestern United States. This plateau covers an area of 336,700 km2 (130,000 mi2) within w ...

, this group of formations was laid down in the

Middle Jurassic The Middle Jurassic is the second Epoch (geology), epoch of the Jurassic Period (geology), Period. It lasted from about 174.1 to 161.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relativel ...

during the

Bajocian In the geologic timescale, the Bajocian is an age and stage in the Middle Jurassic. It lasted from approximately 170.9 ±0.8 Ma to around 168.2 ±1.2 Ma (million years ago). The Bajocian Age succeeds the Aalenian Age and precedes the Bathonia ...

Bathonian In the geologic timescale the Bathonian is an age (geology), age and stage (stratigraphy), stage of the Middle Jurassic. It lasted from approximately 168.2 ±1.2 annum, Ma to around 165.3 ±1.1 Ma (million years ago). The Bathonian Age succeeds ...

and

Callovian In the geologic timescale, the Callovian is an age and stage in the Middle Jurassic, lasting between 165.3 ± 1.1 Ma (million years ago) and 161.5 ± 1.0 Ma. It is the last stage of the Middle Jurassic, following the Bathonian and preceding the ...

Stages Stage, stages, or staging may refer to: Arts and media Acting * Stage (theatre), a space for the performance of theatrical productions * Theatre, a branch of the performing arts, often referred to as "the stage" * ''The Stage'', a weekly Brit ...

Description

The group consists of Jurassic beds younger than the Navajo Sandstone and older than the

Morrison Formation The Morrison Formation is a distinctive sequence of Upper Jurassic sedimentary rock found in the western United States which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltston ...

. These show marine influence in their formation in the northwestern exposures at

San Rafael Swell The San Rafael Swell is a large geologic feature located in south-central Utah, United States about west of Green River. Measuring approximately , the swell consists of a giant dome-shaped anticline of sandstone, shale, and limestone that wa ...

, with formations composed of

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate Hydrate, 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, drywall and blackboard or sidewalk ...

, and

silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension (chemistry), suspension with water. Silt usually ...

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

. Further east, the group becomes more continental in character, with the

Entrada Formation The Entrada Sandstone is a formation in the San Rafael Group found in the U.S. states of Wyoming, Colorado, northwest New Mexico, northeast Arizona, and southeast Utah. Part of the Colorado Plateau, this formation was deposited during the Juras ...

resembling the underlying clean sandstones of the

Glen Canyon Group The Glen Canyon Group is a geologic group of formations that is spread across the U.S. states of Nevada, Utah, northern Arizona, north west New Mexico and western Colorado. It is called the Glen Canyon Sandstone in the Green River Basin of Co ...

. The group is up to thick.

Subunits

Subunits by basin:

Black Mesa Basin Black Mesa (also called Big Mountain) is an upland mountainous mesa of Arizona, north-trending in Navajo County, west and southeast-trending in Apache County. In Navajo it is called ('Black Mountain') and during Mexican rule of Arizona it was ...

: *

Entrada Sandstone The Entrada Sandstone is a formation (geology), formation in the San Rafael Group found in the U.S. states of Wyoming, Colorado, northwest New Mexico, northeast Arizona, and southeast Utah. Part of the Colorado Plateau, this formation was deposi ...

(youngest) *

Carmel Formation The Carmel Formation is a geologic formation in the San Rafael Group that is spread across the U.S. states of Wyoming, Utah, Colorado, north east Arizona and New Mexico. Part of the Colorado Plateau, this formation was laid down in the Middle Ju ...

Page Sandstone The Page Sandstone is a geologic formation in Utah. It preserves fossils dating back to the Jurassic period. See also * List of fossiliferous stratigraphic units in Utah * Paleontology in Utah image:Map of USA UT.svg, The location of the state ...

(oldest)

Great Basin The Great Basin () is the largest area of contiguous endorheic watersheds, those with no outlets to the ocean, in North America. It spans nearly all of Nevada, much of Utah, and portions of California, Idaho, Oregon, Wyoming, and Baja Californi ...

province: *Entrada Sandstone (youngest) *Page Sandstone *Carmel Formation * Temple Cap Sandstone (oldest) Peterson concluded that the Henrieville Sandstone was simply the bleached upper zone of the Entrada Sandstone and recommended abandoning the formation. Palo Duro Basin/Sierra Grande Uplift: *Entrada Formation (youngest) * Bell Ranch Formation (oldest)

Paradox Basin The Paradox Basin is an asymmetric foreland basin located mostly in southeast Utah and southwest Colorado, but extending into northeast Arizona and northwest New Mexico. The basin is a large elongate northwest to southeast oriented depression form ...

: *

Summerville Formation The Summerville Formation is a geological formation in New Mexico, Colorado, and Utah of the Southwestern United States. It dates back to the Oxfordian stage of the Late Jurassic.Wilcox 2007 Description The formation consists of up to of red m ...

(youngest) *

Curtis Formation The Curtis Formation is a geologic formation in Utah. It preserves fossils dating back to the Callovian age of the Jurassic period. Description The Curtis Formation is composed of shallow marine sandstone, with thin beds of mudstone and mino ...

*Carmel Formation *Entrada Sandstone *Page Sandstone (oldest)

Piceance Basin The Piceance Basin is a geologic structural basin in northwestern Colorado, in the United States. It includes geologic formations from Cambrian to Holocene in age, but the thickest section is made up of rocks from the Cretaceous Period. The basi ...

: *Summerville Formation (youngest) *Entrada Sandstone (oldest)

Plateau Sedimentary Province The Colorado Plateau is a physiographic and desert region of the Intermontane Plateaus, roughly centered on the Four Corners region of the Southwestern United States. This plateau covers an area of 336,700 km2 (130,000 mi2) within wes ...

: * Romana Sandstone (youngest) *Entrada Sandstone *Carmel Formation *Page Sandstone

San Juan Basin The San Juan Basin is a geologic structural basin located near the Four Corners region of the Southwestern United States. The basin covers 7,500 square miles and resides in northwestern New Mexico, southwestern Colorado, and parts of Utah a ...

: * Cow Springs Sandstone *

Wanakah Formation The Summerville Formation is a geological formation in New Mexico, Colorado, and Utah of the Southwestern United States. It dates back to the Oxfordian stage of the Late Jurassic.Wilcox 2007 Description The formation consists of up to of red m ...

*Entrada Sandstone southern San Juan Basin: *

Zuni Sandstone The Zuni Sandstone is a geologic formation in west-central New Mexico. It marks the southernmost limit of Jurassic fluvial and lacustrine sedimentary formations, which pinch out to leave a single sandstone body. Description The Zuni Sandstone ...

(youngest) * Bluff Formation *Summerville Formation *

Todilto Formation The Todilto Formation is a geologic formation in northern New Mexico and southeastern Colorado. It preserves fossils dating back to the Callovian stage of the middle Jurassic period. Description The formation consists of evaporites. It is divi ...

*Entrada Sandstone (oldest)

History of investigation

There is no designated type locality for the group. It was named for exposures in the

Emery County, Utah Emery County is a County (United States), county in east-central Utah, United States. As of the 2020 United States census, the population was 9,825. Its county seat is Castle Dale, Utah, Castle Dale, and the largest city is Huntington, Utah, Hu ...

James Gilluly James Gilluly (June 24, 1896 – December 29, 1980) was an American geologist. Regarding the Cupriferous Porphyry Genesis, Gilluly integrated detailed observations of the Ajo porphyry between 1936 and 1936 with experimental data (Goranson, 1931, ...

and J.B. Reeside in 1928. They divided the group into (ascending): Carmel Formation, Entrada Sandstone (new), Curtis Formation (new), and Summerville Formation (new). Areal extent limits were established by

Herbert E. Gregory Herbert Ernest Gregory (October 15, 1869 – January 23, 1952) was a Yale University geologist well known for his early 20th-century explorations of the Colorado Plateau in Arizona and Utah. One of his most important works is ''Colorado Plateau R ...

and

Raymond Cecil Moore Raymond Cecil Moore (February 20, 1892, Roslyn, Washington – April 16, 1974, Lawrence, Kansas) was an American geologist and paleontologist.Daniel F. Merriam (2007), "Raymond Cecil Moore: Legendary Scholar and Scientist, World-Class Geologist a ...

in 1931. Smith in 1954 revised and divided the group into Entrada, Todilto, and Thoreau (new) formations in the

. In 1959 another revision, this time by Griggs and Read, divided it into Entrada and Bell Ranch (new) formations in the Palo Duro Basin and Sierra Grande Uplift. The Carmel-Navajo contact was revised by Wright and others in 1962 and the Carmel-Entrada contact was revised by Phoenix in 1963. Thompson and Stokes created an overview and named the Henrieville Sandstone in 1970. The Temple Cap Sandstone was revised and the Page Sandstone added (new) by Peterson and Pipiringos in 1979. A revision by O'Sullivan in 1980 divided the group into Carmel, Entrada, and Wanakah formations in

. O'Sullivan revised the upper contact in 1984. In 1988 Peterson revised earlier work and divided the group into Page, Carmel, and Entrada formations in the

; divided it into Page, Carmel, Entrada and Romana (new) formations in the

; and divided it into Page, Carmel, Entrada, Curtis, and Summerville formations in Paradox Basin. Condon in 1989 revised the group in

and divided it into Entrada and Wanakah formations in southeastern area; divided it into Entrada, Wanakah, and Cow Springs formations in south-central area; and divided it into Entrada and Cow Springs Sandstones in southwestern area.{{cite journal , last1=Condon , first1=S.M. , title=Revisions of Middle Jurassic nomenclature in the southeastern San Juan Basin, New Mexico , journal=U.S. Geological Survey Bulletin , date=1989 , volume=1808E , pages=E1-E21 , doi=10.3133/b1808EF, doi-access=free

References

Geologic groups of New Mexico Geologic groups of Arizona Geologic groups of Utah Geologic groups of Colorado Middle Jurassic North America Sandstone groups of the United States Mudstone groups Limestone groups of the United States