The Entrada Formation

180-140 million years ago...The Entrada formation spreads across Wyoming, Colorado, Northwest New Mexico and Northeast Arizona, and Southwest Utah. The Entrada formation was deposited during the Jurassic period, between 180 and 140 million years ago. Its location is in Arches National Park. Entrada was formed probably by the sea flowing into the region and evaporating again and again and again. The unstable salt structure caused the surface rock to shift and buckle causing the bottom layer to collapse and the top layer to replace the bottom layer. The Entrada formation lies immediately on the compact limestone of the Carmel formation and below the resistant gypsum beds of the Curtis formation. This formation consists of fine –grain sandstone. It is usually a dark red color banded with white. This includes thin sheets where gypsum can be found. Many lenticular beds of gypsum shale exist in this formation.

Delicate Arch at Arches National Park near Moab, UT.

The upper layer making contact with the bottom layer of the Entrada Formation.