page_title: Geology of the Canyonlands area
section_title: Cutler Group
hierarchical_section_title: Geology of the Canyonlands area / Deposition of sediments / Cutler Group
context_page_description: The exposed geology of the Canyonlands area is complex and diverse; 12 formations are exposed in Canyonlands National Park that range in age from Pennsylvanian to Cretaceous. The oldest and perhaps most interesting was created from evaporites deposited from evaporating seawater. Various fossil-rich limestones, sandstones, and shales were deposited by advancing and retreating warm shallow seas through much of the remaining Paleozoic.
  Eroded sediment from a nearby mountain range later mixed with coastal dune and sand bar deposits. The end of the Paleozoic and the start of the Mesozoic saw the last seas start to leave the region for good. A subdued topography was dominated by flood plains and 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.
  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.
context_section_description: Early in the Permian a transgressing (advancing) sea laid down 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 and Elephant Canyons.
  The Uncompahgre Mountains (Uncompahgre Plateau) were undergoing extensive erosion during this time. Large alluvial fans filled the basin where it met the range. The resulting Cutler red beds are made of iron-rich arkose sandstone. Underwater sand bars and sand dunes on the coast inter-fingered with the red beds and later became the white-colored cliff-forming Cedar Mesa Sandstone. Today these two competing rock units are exposed in a 4 to 5 mile (6.4 to 8 km) wide belt across the park, stretching from south of the Needles through the Maze and to the Elaterite Basin.
  Brightly colored oxidized muds were deposited on top of the Cedar Mesa and ranged in color from red to brown. These sediments eventually became the slope-forming Organ Rock Shale formation and can be seen in the Land of Standing Rocks part of the park.
  Coastal sand dunes and marine sand bars once again became dominant, creating the cross-bedded cliff-forming White Rim Sandstone. It is exposed as a topographic bench 1200 feet (365 m) below the top of Island in the Sky (thus earning its name) and along the White Rim Road. A fossilized offshore sand bar made of the White Cliff Sandstone is also exposed in the Elaterite Basin. A tarry dark-brown oil called elaterite seeps out of the structure, giving the basin its name.
  The Permian sea retreated, which  exposed the land to a long period of erosion and thus created a second unconformity.
caption: White Rim Sandstone overlaying Organ Rock Shale, Canyonlands, Utah.
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