The Mancos Shale or Mancos Group is an Upper Cretaceous

Late Cretaceous

The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...

 geologic formation of the Western United States

Western United States

.The Western United States, commonly referred to as the American West or simply "the West," traditionally refers to the region comprising the westernmost states of the United States. Because the U.S. expanded westward after its founding, the meaning of the West has evolved over time...

 dominated by mudrock that accumulated in offshore and marine environments of the Cretaceous North American Inland Sea

Western Interior Seaway

The Western Interior Seaway, also called the Cretaceous Seaway, the Niobraran Sea, and the North American Inland Sea, was a huge inland sea that split the continent of North America into two halves, Laramidia and Appalachia, during most of the mid- and late-Cretaceous Period...

. The Mancos was deposited during the Cenomanian

Cenomanian

The Cenomanian is, in the ICS' geological timescale the oldest or earliest age of the Late Cretaceous epoch or the lowest stage of the Upper Cretaceous series. An age is a unit of geochronology: it is a unit of time; the stage is a unit in the stratigraphic column deposited during the corresponding...

 through Campanian

Campanian

The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...

 ages, approximately from 95 Ma to 80 Ma. The Mancos Shale was first described by Cross and Purington in 1899 and was named for exposures near the town of Mancos, Colorado

Mancos, Colorado

The town of Mancos is a Statutory Town located in Montezuma County, Colorado, United States. The population was 1,119 at the 2000 census.The town of Mancos is located in southwestern Colorado, near the Four Corners, at the base of Mesa Verde National Park, and holds the trademark for "Gateway to...

. Stratigraphically

Stratigraphy

Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....

 the Mancos Shale fills the interval between the Dakota Group and the Mesa Verde Group.

The Mancos Shale rests conformably on the Dakota and in its upper part grades into and intertongues with the Mesaverde Group. The shale tongues typically have sharp basal contacts and gradational upper contacts.

Occurrences

The Mancos occurs in the Basin and Range Province, the Colorado Plateau Province

Colorado Plateau

The Colorado Plateau, also called the Colorado Plateau Province, is a physiographic region of the Intermontane Plateaus, roughly centered on the Four Corners region of the southwestern United States. The province covers an area of 337,000 km2 within western Colorado, northwestern New Mexico,...

 and the San Juan Mountains Province

San Juan Mountains

The San Juan Mountains are a high and rugged mountain range in the Rocky Mountains in southwestern Colorado. The area is highly mineralized and figured in the gold and silver mining industry of early Colorado. Major towns, all old mining camps, include Creede, Lake City, Silverton, Ouray, and...

, as well as in the following basins:

Black Mesa Basin Estancia Basin Green River Basin Green River (Utah) The Green River, located in the western United States, is the chief tributary of the Colorado River. The watershed of the river, known as the Green River Basin, covers parts of Wyoming, Utah, and Colorado. The Green River is long, beginning in the Wind River Mountains of Wyoming and flowing...

Orogrande Basin Paradox Basin 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 formed during the late Paleozoic Era... Piceance Basin 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...

San Juan Basin San Juan Basin The San Juan Basin is a geologic structural basin in the Four Corners region of the Southwestern United States; its main portion covers around , encompassing much of northwestern New Mexico, southwest Colorado, and parts of Arizona and Utah.... Uintah Basin Uintah Basin The Uintah Basin, also spelled Uinta Basin, is a physiographic section of the larger Colorado Plateaus province, which in turn is part of the larger Intermontane Plateaus physiographic division. It is also a geologic structural basin in eastern Utah, east of the Wasatch Mountains and south of the...

Subunits

The Mancos occurs with the following subunit names (listed alphabetically):

Anchor Mine Tongue (CO,UT), Aspen Member (UT,WY), Black Butte Tongue (WY), Blue Gate Member (UT), Bridge Creek Limestone Member (NM), Buck Tongue (CO,UT), Bull Point Sandstone Member (UT), Carlile Member (NM), Clay Mesa Tongue (NM), Cooper Arroyo Sandstone Member (NM), Emery Sandstone Member (UT), D-Cross Tongue (NM), Devils Grave Sandstone [Member] (CO), El Vado Sandstone Member (NM), Ferron Sandstone Member (CO,UT),

Fort Hays Limestone Member (CO), Fort Hays Limestone Member (CO), Frontier Formation (CO,UT), Garley Canyon Sandstone Member (UT), Graneros Member (CO,NM), Greenhorn Limestone Member (NM), Hartland Shale Beds (NM), Hopi Sandy Member (AZ), Horsehead Tongue (NM), Hunt Creek Sandstone [Member] (CO), Juana Lopez Member (CO,NM), Loyd Sandstone Member (CO), Masuk Member (UT) or Masuk Tongue (UT), Meeker Sandstone Member (CO), Morapos Sandstone Member (CO),

Mowry Member (UT) or Mowry Shale (CO,UT), Mulatto Tongue (NM), Muley Canyon Sandstone Member (UT), Niobrara Member (CO,NM), Pescado Tongue (AZ,NM), Rangely Tongue (CO,UT), Rio Salado Tongue (NM), Sanastee Sandstone Member (NM), Satan Tongue (NM), Semilla Sandstone Member (NM), Tocito Sandstone Lentil (CO,NM), Tununk Member (UT), Whitewater Arroyo Tongue (NM), Wildcat Canyon Sandstone Member (UT), Wind Rock Tongue (AZ).