Utah
Through Time
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These images are from Utah:
a geologic history from Paleozoic to Present , (pdf), PI-54A colorful poster (35" x 18") version representing
some of Utah's geologic history with simple maps and text that explain
how the great forces of nature created the geology that makes Utah's
parks so spectacular.
During this era Utah was at the western edge of North
America. The eastern portion of the state was a low plain with little
relief at about sea level. What little sediment did reach the ocean
was well washed quartz sand. Coral reefs, now exposed as thick limestones
in the Wasatch Mountains, marked shallow seas that led to deep oceans
in the west.
Wind Deposited Sands: Early Jurassic. Cut off from moisture-laden ocean winds by rising mountains
to the west, desert sands were blown into Utah from the north and
northwest. These blowing sands formed dunes which eventually turned
into rock and are preserved in what is now called the Navajo Sandstone.
These ancient dunes are well exposed at Checkerboard Mesa in Zion
National Park and on the San Rafael Swell.
Famous Dinosaurs: Late Jurassic. At this time Utah was a hot, swampy lowland with mountains
and volcanoes to the west and northwest. Meandering rivers and lakes
abounded, while dinosaurs roamed the land. Their fossilized bones
are preserved and can be seen at famous sites such as the Cleveland-Lloyd
Dinosaur Quarry and Dinosaur National Monument.
Coal Formations: Late Cretaceous. Pressure from continental collisions with the Pacific
Plate to the west produced high mountains in western Utah. The eastern
portion of the state was covered by an inland sea that stretched
from the Gulf of Mexico to the Arctic. The costal plain between
these two areas advanced and retreated as sediment filled the sea
and the basin sank. Coal swamps formed behind barrier islands while
dinosaurs continued to rule.
Utah Starts to Come Up in the World: Paleocene . Erosion wore down the mountains to the west and sediments
filled the inland sea to the east. Continued pressure from the Pacific
Plate caused both the Uinta Mountains and the Colorado Plateau to
uplift. The Colorado Plateau warped as it rose, making the beginning
of predominate swells and depressions now found in Utah (such as
the San Rafael Swell). A large freshwater body, called Lake Flagstaff,
occupied a depression in what is now central Utah.
Oil Shale and Fossil Fish: Eocene. After spending nearly 500 million years near sea level,
Utah continued its rise to nearly a mile high in elevation. Continued
warping of the Colorado Plateau produced basins for lakes such as
Lake Uinta. Organic-rich accumulations in the bottom sediments include
well-preserved fish fossils and oil shales. The western mountains
were reduced to relics.
Uplift and Volcanics: Oligocene. On the Colorado Plateau the lake basins were filled
in and broad plains separated mountain uplifts. The beginning of
modern rivers ran across these plains. The continental divide passed
through northeastern Utah so the Green River in Wyoming drained
to the Mississippi River. With the beginning of extension in western
Utah, which would eventually lead to the Basin and Range, extensive
volcanic activity started to occur.
Precious Metals Emplaced: Miocene. Whereas previous compression had moved the site of San
Francisco closer to Salt Lake City, extension was now moving the
two apart. This extension separated uplifted mountain blocks from
down-dropped basins forming the Basin and Range. Volcanic activity
continued forming three great metallic mineral belts. From north
to south they are: Park City-Oquirrh, Deer Creek-Tintic, and Wah
Wah-Tushar. The Colorado Plateau continued to rise and tilt northeastward.
Water and Ice: Pleistocene. The geography of Utah was very close to what it is now.
Mountains, canyons, and rivers were all well in place. The climate
at this time was wetter and colder and as a result glacial activity
took place. Canyons were carved and expanded in the Uinta Mountains
as well as in several other mountain ranges throughout the state.
A giant fresh-water body called Lake Bonneville also formed, stretching
from the Wasatch Mountains to Nevada and from the Utah-Idaho border
nearly down to Cedar City in southern Utah.
These are the Places: Present. The geologic history of Utah has left an indelible mark
on the state. It explains why the rocks to the east are brightly
colorful while those to the west have somber colors, why there are
spectacularly massive canyons on the Colorado Plateau while much
of the Basin and Range has no external drainage, and why a high
mountain chain, the Wasatch, runs down the middle of the state.
This history determines the location of settlements, industry, and
recreation sites.
