AS YOU APPROACH Dinosaur National Monument from Jensen, Utah, you see
the mass of Split Mountain and the deep, short canyons that scar its
south slope near the Green River's gorge. As you cross the National
Monument boundary the grand view is lost and you begin to notice
details. The masses of gray shale that seem to be carelessly piled
against the tilted sandstone layers are bare of vegetation. The ground
between the hills and the Green River is covered with sagebrush and
greasewood, while along the river itself are a few large cottonwood
trees and many bushes. A sharp turn brings a change of scene as your car
enters a portal in the wall you have been following. The pronounced tilt
of the rocks becomes more obvious.
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JURASSIC LANDSCAPE SHOWING ANIMALS AND PLANTS
THAT LIVED HERE DURING MORRISON TIME. (from a painting by Ernest
Unterman.)
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A final steep climb and the visitor center is at hand. This building
encloses a significant part of the Dinosaur Quarry, perhaps the greatest
deposit of fossil dinosaur bones known today. From this quarry have come
many of the dinosaur skeletons that are seen today in our great museums.
After parking, a short walk to the overlook on the southeast reveals a
splendid view of Split Mountain. Between that broad arch of eroded
sandstone and the quarry lie steeply tilted sedimentary rocks of various
compositions and hues. Buff and gray sandstones that weather into soft
shapes are separated by reddish-brown shale. Directly to the east is a
section of varicolored shale whose pastel pinks, reds, greens, grays,
and whites justify the name of "rainbow beds" that was given them by
geologists. In the upper part of this section are hard sandstone and
limestone layers that resist the erosive action of wind and water. They
stand higher than the softer shales and form hogbacks that rim Split
Mountain.
One of these layers can be traced across the ravine immediately east
of the parking area into the sandstone ledge that forms the north wall
of the visitor center. This is the famous Dinosaur Ledge.
The Quarry
The Dinosaur Ledge is famous because here the world's greatest store
of fossil bones of these long extinct reptiles has been uncovered. Two
groups, or orders, of dinosaurs have been discovered, with a number of
different types or kinds somewhat related to each other within these
orders. From the fossil bones, scientists can tell that these creatures
varied greatly in size and habits of living.
Some were the size of chickens, others as big as horses, and others
of such gigantic size that no land animal alive today can compare with
them. Some were flesh-eaters as indicated by the size and shape of their
teeth and their long sharp claws. Others were plant-eaters and again it
is the structure of their teeth and feet that tell us this. The
flesh-eaters were two-footed and walked on their hind legs, balancing
themselves with heavy long tails. Their short front legs were used as
clawed-arms for tearing at the flesh of other dinosaurs. Many
plant-eaters, on the contrary, were large, heavy, four-footed beasts,
often with long necks and tails. Many of the dinosaurs were land
dwellers and many others lived in the great marshes and swamps of the
long Mesozoic (middle life) Era of the earth's history.
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TILTED ROCK STRATA NEAR THE DINOSAUR QUARRY.
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Though the subclass of reptiles we call dinosaurs lived all through
the Mesozoic Era, those whose fossil bones have been uncovered in this
Dinosaur Quarry are embedded in a stratum of rock called the Morrison
formation. This rock stratum dates from the Jurassic Period in the
middle of the Mesozoic Era.
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