Morrison Formation

The Morrison Formation in Arches National Park.
The Morrison Formation in Arches National Park.

NPS photo by Neal Herbert


The Morrison Formation is composed of three members (listed from youngest to oldest): Brushy Basin, Salt Wash and Tidwell. Each has different characteristics due to changes in the depositional environment. This layer does not occur in Canyonlands.

Late Jurassic (144 to 208 million years ago)

Depositional Environment:
Varied between river, tidal flat and shallow marine


  • Brushy Basin: multicolored Bentonite clays (volcanic ash)
  • Salt Wash: Light-colored, ledge-forming sandstone
  • Tidwell: red marine sandstones frequently containing chert

Visible in the northern parts of Arches National Park (Salt Valley) and along Highway 191 north of Moab

The Salt Wash Member is a source of uranium which was mined throughout the Moab area. Dinosaur tracks and fossils also appear in the Morrison Formation.

Rock Strata
Layer Above: Burro Canyon / Cedar Mountain Formation
Current Layer: Morrison Formation
Layer Below: Sommerville Formation

Last updated: December 14, 2015

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