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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