thumb| Entrada Sandstone conformably overlies the Carmel Formation, Park Avenue, [[Arches National Park ]]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 Jurassic Period sometime between 180 and 140 million years ago in various environments, including tidal mudflats, beaches, and sand dunes. The Middle Jurassic San Rafael Group was dominantly deposited as ergs (sand seas) in a desert environment around the shallow Sundance Sea.

Description

At its type section at Entrada Point, located in the northern part the San Rafael Swell in Emery County, Utah,

In the San Juan Basin of northwestern New Mexico, the Entrada consists of upper and lower sandy members and a medial silty member, the Rehoboth Member. The Curtis Formation is sometimes absent and the Entrada then overlies Chinle Formation. It is overlain by the Todilto Formation. Southeast of Fort Defiance, Arizona, the lower sandy beds are assigned to the Iyanbito Member. Total thickness is up to .

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File:Entrada Sandstone capped by Curtis Formation in Cathedral Valley.jpg|Entrada Sandstone overlain by Curtis Formation in Capitol Reef National Park's Cathedral Valley

File:Entrada at Curtis Pt.jpg|Entrada Formation at Curtis Point, Emery County, Utah.

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History of investigation

The Entrada Sandstone was named as one of the four formations of the San Rafael Group by James Gilluly and Reeside in 1928. Gregory and Moore worked out the geographic extent of the formation and gave an overview of it in 1931. The extent was revised several times afterwards (most recently in 1992 by Condon). It was divided into the Gunsight Butte, Cannonville, and Escalante members by Thompson and Stokes in 1970. The principal reference for the formation was written in 1988 by Peterson.

Members

Entrada members are (in alphabetical order<!-- order by age needed -->):

  • Cannonville Member (UT) Now assigned to the Carmel Formation.
  • Gunsight Butte Member (UT)
  • Moab Member (CO, UT) or Moab Tongue (CO, UT) - named after the type locality of Moab, Utah. The whitish sands from inland dunes make up this "cap rock" layer, as seen atop Delicate Arch and Broken Arch in Arches National Park.
  • Green River Basin
  • Las Vegas-Raton Basin
  • North Park Basin
  • Paradox Basin