Utah Colorado
The Green River makes a hairpin turn around a sandstone fin just before meeting the Yampa River in Dinosaur National Monument.
Straddling the border between northeast Utah and northwest Colorado, Dinosaur National Monument is home to more than 200,000 acres of geological and paleontological bounty. Commercial airline flights are unlikely to fly over the park—the deep river canyons and high rocky ridges are located on a remote southeast flank of the Uinta Mountains. After hearing its story, though, you may want to make a point of seeing it from a more down-to-earth perspective.
Thanks to a fortuitous set of circumstances, the rock layers exposed at Dinosaur National Monument cover a remarkable span—over 1.2 billion years, from the Precambrian Era to the Miocene Epoch, the youngest dating to around 10 million years ago. Out of all the official rock layers laid down through geologic history, only three are missing from the exposed rocks at Dinosaur: the Ordovician, Silurian, and Devonian layers, wiped from the record by erosion. The twenty-three layers that are visible make up the most complete exposed stratigraphic column within the U.S. National Park system. As evidenced by the site’s name, the most famous layers on display at Dinosaur National Monument are those from the Mesozoic Era—the time of the dinosaurs.
Sedimentary layers of rock from the time of the dinosaurs are the most well-known geologic layers in Dinosaur National Monument.
All that exposure is the work of the Green and Yampa Rivers, which meet in the monument. As the land was uplifted during the Laramide orogeny, which built the Rocky Mountains, and during later episodes of regional uplift of the Colorado Plateau, the rivers continued to cut downward through layers, exposing the park’s impressive stratigraphy.
Dinosaur bones were first discovered in the area in the late 1800s, but petroglyphs of dinosaur-like reptiles found in the area suggest that ancient people were also curious about the large bones they found weathering out of the Mesozoic layers. In the early years of exploration, more than 350 tons of fossils were removed from the quarries in the area and shipped east, most to the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania, where many are still on display.
The 800-plus quarries in the area, some of which are still actively mined, are famous not just for the quantity of fossils they have produced, but for the diversity of species represented and the quality of preservation. A wide range of dinosaurs have been uncovered here, from giant carnivores such as Allosaurus and massive sauropods with long whip necks and tails, to vegetarians like Stegosaurus and tiny bird-like species.
Most of the fossils appear to have collected in ancient river beds, where dead animals were entombed in sediment that was later deeply buried and lithified into rock, preserving the bones as mineralized fossils. Despite this potentially chaotic method of burial, a few skeletons have been found fully intact and articulated—with all bones in place. Other quarries have uncovered jumbled masses of fossils from many different species, possibly washed together in flash floods. An example of this kind of burial can be seen in the Dinosaur Quarry visitor center on the Utah side of the park. The building was constructed around the Quarry Exhibit Hall, a trove of 1500 dinosaur bones that have been preserved in place, as they were found.
Dinosaur National Monument’s Quarry Exhibit Hall allows visitors to see dinosaur fossils preserved in place, likely washed into a jumbled mass by floodwaters.
A petroglyph of a dinosaur-like reptile suggests that Native Americans were aware of the fossils in the area long before they were discovered by modern paleontologists.
Dinosaur National Monument is located in a secluded area of eastern Utah and northwest Colorado. You could fly over it en route to Salt Lake City, Utah.
