processes have played the most important part in shaping
the desert ecosystem of Canyonlands. The arid climate
and sparse vegetation allow the exposure of large expanses
of bare rock, while the deep canyons of the Colorado and
Green Rivers reveal 300 million years of geologic history.
Evolution of Canyons:
Canyonlands is located within a geologic region called
the Colorado Plateau. For millions of years, water and
wind deposited materials from a variety of environments
onto what is now the Colorado Plateau. The area was repeatedly
flooded and then dried by intense sun and wind, and the
remains of these ancient seas and deserts were slowly
compressed into layers of sedimentary rock. Massive geologic
uplifts to the east and north brought torrents of mountain
rain and snowmelt, carving the deeply incised river channels
of the Green and Colorado rivers. 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 around Canyonlands are flat. However,
massive folds and faults in the land resulted from a thick
layer of salt that shifted under the weight of the overlying
sandstone. In many places, this movement caused the surface
rock to fracture or collapse downward, forming "synclines"
and "anticlines" (see glossary). Over time,
flash floods and the action of water freezing and thawing
enlarged these fractures and eroded the sandstone features
into the landscape seen today.
Many cliffs in the Canyonlands basin show classic
profiles which can be seen throughout the southwest. The
layers were formed out of a variety of materials during
different periods of geologic time. When and how the layers
were deposited has great bearing on how they look today.
The layers are listed here in descending order (going
back in time). See:
varnish is the thin red to black coating found on exposed
rock surfaces in arid regions. Varnish is composed of
clay minerals, oxides and hydroxides of manganese and/or
iron, as well as other particles such as sand grains and
trace elements. The distinctive elements are Manganese
(Mn) and Iron (Fe). See:
About ten million years ago, the Colorado Plateau
was pushed up thousands of feet and rivers, such as the
Colorado and the Green, cut down and carved deep canyons.
Water, the primary force of erosion, eats away or weathers
rock by attacking the cement holding the sand grains together.
Moreover, during storms, rushing water knocks loose sand
and rocks as it flows down washes causing additional erosion.
The water naturally acts faster on areas of weakness within
the rock, such as fractures and cracks. The Needles occur
in an area with many fractures called joints.
Canyonlands is a place of relative
geologic order. Layers of sedimentary deposits systematically
record chapters in the park's past. With some exceptions,
these layers have not been altered, tilted or folded significantly
in the millions of years since they were laid down by
ancient seas rivers or winds.