Moenkopi Formation

Moenkopi Formation Stratigraphic range: Lower Triassic Middle Triassic
Rock layers of the Moenkopi Formation in Zion National Park
Type	Geological formation
Sub-units	See "Members" section
Overlies	Kaibab Limestone
Lithology
Primary	Sandstone
Location
Region	Northern Arizona Southeast California East-central Nevada Southern Utah Northwestern New Mexico Southwestern Colorado
Country	Southwestern United States

The Moenkopi Formation is a geological formation that is spread across the U.S. states of New Mexico, northern Arizona, Nevada, southeastern California, eastern Utah and western Colorado. This unit is considered to be a group in Arizona. Part of the Colorado Plateau and Basin and Range, this red sandstone was laid down in the Lower Triassic and possibly part of the Middle Triassic, around 240 million years ago.

There is no designated type locality for this formation. It was named for a development at the mouth of Moencopie Wash in the Grand Canyon area by Ward in 1901. In 1917 a 'substitute' type locality was located by Gregory in the wall of the Little Colorado Canyon, about 5 miles below Tanner Crossing in Coconino County, Arizona. While in the Great Basin, Bassler and Reeside characterized and named the Rock Canyon Conglomerate, Virgin Limestone, and Shnabkaib Shale members in 1921. Salt Creek (later replaced by Wupatki and Moqui Members) and the Holbrook Member were found and named in the Black Mesa basin by Hager in 1922.

The Sinbad Limestone Member was named in the Paradox Basin by Gilluly and Reeside in 1928. Gregory named the Timpoweap Member in the Plateau sedimentary province in 1948.

The Wupatki Member was first used in the Plateau sedimentary province and its age was modified to Early and Middle(?) Triassic by McKee in 1951. Contacts were revised by Robeck in 1956 and Cooley in 1958. The Tenderfoot, Ali Baba, Sewemup, and Pariott Members were named in the Piceance and Uinta Basins by Shoemaker and Newman in 1959. The Hoskinnini Member was assigned in the Black Mesa and Paradox basins by Stewart in 1959. Contacts were revised again by Schell and Yochelson in 1966. Blakey named the Black Dragon, Torrey, and Moody Canyon members in the Paradox Basin and Plateau sedimentary province in 1974. Contacts were revised yet again by Welsh and others in 1979.