tidal flats. Now much further inland, the Triassic climate in the region was dry. Vast deserts covered much of that part of North America, except for one period when streams for a time fought the sand dunes. Wetter times returned in the Cretaceous as the area was flooded by the Western Interior Seaway
.
The uplifting of the Rocky Mountains starting in late Cretaceous - greatly affected the Canyonlands region. Erosion rates increased and further quickened the onset of the ice ages in the Pleistocene. Modern-day erosion occurs at a slower rate.
Deposition of sediments
Hermosa Group
A vast sea covered the region in early
Uncompahgre Mountains was uplifted to the east. Great quantities of seawater were trapped in the subsiding basin and water became increasingly saline in the hot and dry climate. Thousands of feet of evaporites (anhydrite and gypsum then halite) started to build up in the Mid Pennsylvanian and storms occasionally washed sediment from the nearby mountains. Fresh seawater periodically refilled the basin but was never able to flush out the very salty water there (the new water in fact floated on top of the brine). These beds were later lithified to become the Paradox Formation, which in turn is part of the Hermosa Group
.
Compressed salt beds from the Paradox started to flow plastically later in the Pennsylvanian and probably continued to move from then until the end of the Jurassic. Satellite-based measurements indicate that flow of salt and gypsum continues today to cause flexing and faulting of overlying sedimentary layers.
The Paradox is up to 5000 feet (1520 m) thick in places and in the park is exposed at the bottom of Cataract Canyon as rock gypsum inter-bedded with black shale. Upward movement of the Paradox is also a possible theory for the creation of Upheaval Dome, although none of the Paradox is exposed on the dome, the predominant theory being a meteor crater.
A warm shallow sea again flooded the region near the end of the Pennsylvanian. Limey oozes, sand, and mud were deposited on top of the salt-filled basin. These sediments became the
Colorado River
.
A period of erosion then ensued, creating a break in the geologic record called an unconformity.
Cutler Group
Early in the
Halgaito Shale. Coastal lowlands returned to the area after the sea regressed (retreated), forming the Elephant Canyon Formation. These formations can now be seen in Cataract