Dinosaur National Monument
By Kaitlin McCormick, 2003
Figure 1. A map of Dinosaur National Monument
Straddling the border of northwest Colorado and northeast Utah, Dinosaur National Monument is approximately 210,000 acres (Figure 1). Earl Douglass discovered the fossils that give the monument its name in 1909. Douglass was working for the Carnegie Museum of Pittsburgh, Pennsylvania, as a paleontologist and he knew that some of the rocks in northeastern Utah were the same kind that had produced dinosaur skeletons elsewhere. He went to the area now known as Dinosaur National Monument hoping to find more bones for the museum. The dinosaur skeletons in this area were numerous and Douglass spent many years digging and shipping the skeletons to Pittsburgh where they are now on display. In 1915, President Woodrow Wilson proclaimed the site as Dinosaur National Monument after he had heard about the great dinosaur quarry. National Park Service began to develop the quarry as it is today several years later (Figure 2). One wall of the Quarry Center is the rock layer that contains the fossil bones. Paleontologists have carefully removed rock to uncover the bones yet leaving them in place allowing more than 1,500 fossil bones to be exposed for visitors (Figure 3).
Figure 2. The Visitor’s Center containing the quarry
Figure 3. The quarry wall showing fossils.
Although the Monument is best known for its fossils, the magnificent canyons
cut by the Green and Yampa River expose rock strata that record over a billion
years of Earth’s history. The basement rocks are Proterozoic in age, the
Uinta Mountain Group. The Uinta Mountain Groups consists predominately of ancient
quartz sandstone that is commonly interbedded with siltstones and gray, olive
green, and red micaceous shales. To see the Stratigraphic column for Dinosaur
National Monument, please click here for MSWord
or here for PDF.
The Paleozoic Erathem consists of a transgressive sequence of coarse sandstone,
overlaying finer grain sandstones and shales, then finally by slightly dolomitized
limestone that is fossiliferous. There is some repetition to the pattern, especially
in the Pennsylvanian System where marine limestone is topped by sandstone. The
Erathem is capped by eolian cross-bedded sandstone. Important formations include
the Late Cambrian Lodore Formation, the Middle Pennsylvanian Morgan Formation,
and the Permian Park City Formation.
The Mesozoic Erathem contains the rocks that are the source of the fossils for which the park is named. The main rock type is shale; the thickest formation, ranging from 1,450 to 1,700 meters, is the Mancos Shale. The minor rock types include sandstones, silt- and mudstones. The major formations include the Late Triassic to Early Jurassic Glen Canyon Sandstone, the Middle Jurassic Entrada Sandstone and Late Jurassic Morrison Formation, where the dinosaur fossils are found.
There are eleven species of Dinosaurs found in the quarry. The main group is
the sauropods. Fossil specimens of this group found are Apatasaurus, Camarasaurus,
Barosaurus, and Diplodocus. The other dinosaurs are Stegosaurus, Dryosaurus,
Camptosaurus, Ornitholestes, Allosaurus, and Ceratosaurus.
The Cenozoic Erathem consists of two main formations at base, the Oligocene
Bishop Conglomerate and Miocene Browns Park Formation. The rest of the units
in the Erathem can be grouped together and called surficial deposits. The sources
used differentiated the surficial deposits. The formations are mainly fan deposits,
alluvium, colluvium, tallus, and channel deposits.
The fossiliferous rock units were exposed due to folding and faulting that occurred during the Laramide Orogeny, about 70 to 40 million years ago. This allowed the rocks to be eroded into the current plateau- and canyon-dominated landscape (Figure 4).
Figure 4. Overview of the canyons and plateaus
References:
Gregson, J.D. and D.J. Chure, Geology and Paleontology of Dinosaur
National Monument, Utah-Colorado, Geology of Utah’s Parks and Monuments,
2000 Utah Geological Association Publication 28.
The National Park Service, The Dinosaur National Monument Webpage http://www.nps.gov/dino/index_old.htm