Dinosaur Hill is located within the McInnis Canyons National Conservation Area and is owned/managed by the Bureau of Land Management, the Museums of Western Colorado, and the City of Fruita. The historic Riggs quarry site was donated by the Eugene Fletcher family, and the kiosk was built by Lyle Nichols with funding from the Colorado Lottery.
Paleontology of Dinosaur Hill
Paleontologist Elmer S. Riggs, assistant curator of geology at the Field Columbian Museum in Chicago (now, the Field Museum of Natural History), and his crew of one field assistant/photographer and a field assistant/camp cook excavated a quarry on the east side of Dinosaur Hill during the summer of 1901. The previous year, the crew had excavated the first Brachiosaurus ever discovered, from a site near Grand Junction (now, Riggs Hill). The crew camped under cottonwood trees along the banks of the Colorado River (then, the Grand River) not far from here and worked the dinosaur quarry each day. The crew would have to ferry both equipment and bones across the river. When the dinosaur they were chasing turned out to run straight into Dinosaur Hill, they enlisted the help of local miners to blast a tunnel into the hillside. They found the back half of the skeleton of a 70-foot-long plant-eating dinosaur called Apatosaurus at this quarry. This skeleton is still mounted at the Field Museum of Natural History in Chicago.
Elmer Riggs was intrigued by this skeleton and began a study of these animals and others similar to it. Based his results, he concluded in 1903 that Apatosaurus and Brontosaurus were two names for the same type of animal, the only differences were changes in the skeleton due to age. And since the name Apatosaurus had been published first, it had priority, and the name Brontosaurus was no longer valid. However, the name persisted in pop culture long after that.
Between 1992 and 2004 paleontologists from the Museums of Western Colorado excavated on west side of Dinosaur Hill and found an assortment of animal fossils from the same rocks as Riggs’ Apatosaurus quarry. These included a juvenile Camarasaurus, a juvenile Stegosaurus, turtles, crocodiles, meat-eating dinosaurs, a small lizard-like reptile called a sphenodontid, and a specimen of the rare flying reptiles known as pterosaurs. All these were found in a quarry the size of a dining-room table!
In 1900, Elmer Riggs, a paleontologist at Chicago’s Field Columbian Museum, set out to the Grand Valley to collect dinosaurs. Led here through correspondence from Dr. S.M. Bradbury of Grand Junction, Riggs was inspired by the news that ranchers had been collecting fossils in this area since it was first settled in the 1880s.
On the south slope of this hill in rocks of the Jurassic-age Morrison Formation, Riggs and his field assistants discovered and excavated a previously unknown dinosaur. Riggs assigned the name of Brachiosaurus altithorax (deep-chest arm-lizard) because the front legs were much longer than those in the back and the ribs were nearly 9 feet long. In honor of Riggs’ discovery, this hill was named after him, and the site of his quarry is marked with a stone monument.
The dinosaur specimen was discovered on July 4, 1900, but work on it did not begin until three weeks later because Riggs and his crew were finishing work at another site near what is now the east entrance to Colorado National Monument. Riggs recognized very quickly that what they had found was at the time the largest dinosaur known. It remained the largest known for 70 years. The crew took about six weeks to dig up the dinosaur, and by mid-September they were on their way back to Chicago.
In 1937 on the northwest slope of this hill, Edward Holt discovered partial skeletons of Allosaurus and Stegosaurus. Hoping the area would become a natural research center, Holt left the bones in the rock. Unfortunately, the bones and other scientific information have been lost through vandalism.
Geology of Riggs Hill
Riggs Hill is composed of two distinct geologic units: the upper part of the Jurassic-aged Morrison Formation (~152 million years old) and the Cretaceous-aged Burro Canyon Formation (~110 million years old). These two formations can be easily picked out on the hillside: the red and grey banded mudstones that form the slopes of Riggs Hill are part of the Morrison Formation, and the hard, blocky, black and brown sandstone that caps the hill, and also is eroding down the sides, is the Burro Canyon Formation. Throughout the Grand Valley, dinosaur bones are found in both of these rock units, including at Dinosaur Hill in Fruita and at the Trail Through Time and Mygatt-Moore Quarry in Rabbit Valley.
Looking south, towards Colorado National Monument, more geologic formations can be seen; the cliff sandstones of the Wingate and Entrada formations are the most prominent from a distance. What formations make up Independence Monument? Can you find these formations on the stratigraphic column? Are they older or younger than the rocks at Riggs Hill?
Why are the older rocks over in Colorado National Monument higher than those found on Riggs Hill, which are younger?
At the base of the cliffs that mark the boundary of Colorado National Monument there is a break in Earth’s crust called the Redlands Fault. This fault has dropped the younger rock units north of the monument lower and thrusted the older rock formations in the monument up higher. This is why the Triassic Chinle Formation at the base of the monument appears to be at the same elevation as the Late Jurassic Morrison Formation at Riggs Hill.