Tuesday, February 23, 2021

Geological Destination - Dead Horse Point State Park

 Just outside of Moab, UT, lies a State Park with fantastic overlooks and great geology. We stopped at Dead Horse Point State Park on our way to Canyonlands National Park back in March of 2019. The two parks are pretty close to each other and we had heard good things about the state park. And we were not disappointed.

The name of Dead Horse Point comes from a legend where cowboys would fence off wild mustang horses along the overlook, taking what horses they wanted and leaving the horses they didn't penned up to die of thirst. But despite the grizzly imagery, this is a beautiful location.

Looking off towards the southeast from the overlook is the Colorado River far below. Between us and the river lies 100 million years of geological history. From top (youngest) to bottom (oldest) the rock units go like this:

Entrada Formation: Jurassic (150 million years old) - This is a sandstone formed from a coastal dune environment. These are what the arches at Arches National Park are found in.

Navajo Sandstone: Jurassic (175 million years old) - Wind deposited, prehistoric "petrified" sand dunes from an ancient erg (sand sea), colored a light tan or white color. The units also preserve phenomenal cross bedding features from the sand dunes. These rocks form the majority of the rock formations in Zion National Park.

Kayenta Formation: Late Triassic (180 million years old) - A series of sandstones, shales, and limestones from a meandering river environment that frequently preserves dinosaur tracks. This formation is very well observed in the nearby Canyonlands National Park.

Wingate Sandstone: Triassic (200 million years old) - Like the Navajo, another wind deposited preserved series of sand dunes, however usually with more of a red tint to the rocks (rust). 

Chinle Formation: Triassic (210 million years old) - A stream deposited series of mudstone, sandstone, and conglomerates. Well known for containing uranium deposits, petrified wood, and fossils. You can see some of the ancient uranium mines in nearby Capitol Reef National Park.

Moenkopi Formation: Early Triassic (230 million years old) - A tidal flat deposited series of brown to red mudstones. The rocks will often feature ripple marks and raindrop imprints. You can see this formation especially well along the western entrance to Capitol Reef National Park.

Cutler Formation: Permian (250 million years old) - Comprised of sandstone and conglomerate, this formation was deposited along a coastal-marine beach with off-shore sands and non-marine alluvial floodplain deposits intermixed. The most notable feature of the Cutler is the White Rim Sandstone.

Honaker Trail Formation: Pennsylvanian to Permian (286-320) - Down at the level of the river lies this shallow sea deposit comprised of dark grey limestones with fossils. 

Off in the distance to the east of the Point are some Solar Evaporation Ponds. These are rather striking in the sea of reds and browns that I'm glad they had an interpretive sign to help understand what you are looking at. 

Description of the salt deposits being mined.

This entire area is part of the Colorado Plateau and is the reason that we have the Colorado River formed within the canyons as you can see here. Over 10 million years ago the Colorado River was flowing along a gently sloped floodplain, being allowed to meander as it needed to. Then the area was forced upwards. This occurred when the Farallon Plate, a large plate that was subducted below North America off the western coast of the the US, began to push upwards on the region. As the region was forced upward, the rivers that were formally allowed to meander naturally, started to erode downwards into the underlying bedrock. This downward erosion locked the rivers in place, creating a feature known as an entrenched meander. Besides just here, you can see this feature all over the Colorado Plateau including at the Grand Canyon National Park, Natural Bridges National Monument, and Goosenecks State Park.

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