• Spires of Cedar Mesa sandstone in Chesler Park (Needles District)

    Canyonlands

    National Park Utah

Morrison Formation

Website (nps
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.

Deposited:
Late Jurassic (144 to 208 million years ago)

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

Appearance:

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

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

Notes:
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.

Did You Know?