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Geologic
processes have played a very important part
in shaping the desert ecosystem of southeast
Utah. Throughout the area, canyons and faults
have exposed millions of years of geologic history.
Deposition
For over 300 million years, water and wind deposited
materials from a variety of environments onto
what is now the Colorado Plateau. The depositional
regimes included shallow marine seas, tidal
flats, freshwater stream systems, alluvial fans,
swamps and Sahara-like deserts. Over time, the
remains of these various environments were cemented
into the layers of sedimentary rock visible
today.
Erosion
Roughly 15 million years ago, the Colorado Plateau
began slowly uplifting. As the Green and Colorado
rivers cut through the layered sandstones, they
became trapped and carved the deep, meandering
canyons we see today. Water from nearby mountain
ranges like the Abajos, La Sals, and Henrys
drains into these rivers, eroding the landscape
further into a network of tributary canyons.
Most
of the rock stata on the Colorado Plateau are
flat. However, significant faulting occurred
in some areas when a deep layer of salt called
the Paradox Formation liquified under the weight
of overlying sandstones. The shifting salt caused
the surface rock to bow and fracture or, in
some cases, to collapse downward. The result
of this movement is dramatic in both Arches
and the Needles District of Canyonlands. Over
time, floods and the action of water freezing
and thawing enlarged these fractures and eroded
the sandstone into a variety of spectacular
shapes.
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