The Entrada Formation is composed of three members (listed from youngest to oldest): Moab Tongue, Slickrock and Dewey Bridge. Each has different characteristics due to changes in the depositional environment. The Arches of Arches National Park are usually in the Slickrock Member. This layer does not occur in Canyonlands.
Mid- to late-Jurassic (144 to 208 million years ago)
Varied between tidal flat (Dewey Bridge) to near-shore sand dunes.
Moab Tongue: Thin, red layer not heavily cross-bedded.
Slickrock: Red, cross-bedded, arch-forming sandstone.
Dewey Bridge: Lumpy, misshapen red sandstone
Entrada is one of the dominant sandstones in Arches National Park.