Stretching north from Morrison to just south of Golden, Dinosaur Ridge became famous for the dinosaur fossils and tracks discovered there in 1877. The discoveries, which included the world’s first known Stegosaurus and Apatosaurus fossils, helped launch a “dinosaur rush” in the late nineteenth century. New fossils and tracks continue to be found on the ridge, which is protected by county, state, and federal designations.
The rock layers that make up Dinosaur Ridge contain many millions of years of history. During the Jurassic period, about 145 million to 201 million years ago, the area that is now Colorado consisted of a low plain crossed by slow-moving rivers. Dinosaurs lived and died along the rivers. Sometimes their bones were fossilized in the river mud and sand. Rock layers from this period are now known as the Morrison Formation.
Later, during the Cretaceous period, eastern Colorado was submerged under an inland sea from about 110 million to 70 million years ago. What is now the Front Range served for a time as a “freeway” for dinosaurs migrating along the western edge of the inland sea. The rocks from this period are now called the Dakota Group. As sea levels continued to rise, much of Colorado was eventually under water.
About 65 million years ago the sea drained, and a sudden uplift called the Laramide orogeny formed huge mountains where the Rockies are today. This activity tilted the old inland seabed at up to a 45-degree angle. Around 40 million years ago, however, the mountains began to quickly erode. A volcanic period known as the Ignimbrite Flare-Up buried them under ash.
As a result of the flare-up and further erosion, the area we know as the Front Range was essentially a continuation of the Great Plains as recently as 5 million years ago. At that point a period of intense erosion began, washing away softer rock layers to reveal the much older and harder rocks that make up the Rocky Mountains. The old tilted seabed layers came to the surface as a long chain of ridges, or hogbacks, at the edge of the foothills. Dinosaur Ridge is one of those hogbacks.
Early Fossil Discoveries
Arthur Lakes (1844–1917) discovered the first known fossils on Dinosaur Ridge in 1877. Originally from England, Lakes attended Oxford University before immigrating to the United States in the 1860s. He had arrived in Colorado Territory by 1867. He became a geology instructor at Jarvis Hall in Golden, which developed into the Colorado School of Mines in the 1870s, and he also served as an Episcopal minister, preaching in nearby mining towns.
On March 20, 1877, Lakes and Henry C. Beckwith, a retired naval officer, were exploring the west side of the hogback just north of Morrison when they came across some large fossilized bones. Lakes recognized them as similar to dinosaur fossils he had seen in England. He sketched the bones and sent his drawings, along with a description of the find, to the paleontologist Othniel Charles Marsh at Yale University. “A few days ago,” he wrote, “I discovered . . . some enormous bones apparently a vertebra and a humerus bone of some gigantic saurian in the Upper Jurassic or Lower Cretaceous at the base of Hayden’s Cretaceous No. 1 Dakotah group.”
Lakes continued to explore the area. In late April he sent a second letter to Marsh, saying he had found a huge femur indicating an animal about sixty feet long. Marsh, one of the most famous paleontologists in America, did not respond. Nevertheless, in May Lakes shipped Marsh about 2,000 pounds of bones and rocks he had excavated from his quarry near Morrison. Lakes also sent a letter and some bones to Marsh’s main competitor, Edward Drinker Cope, with whom Marsh had a bitter rivalry.
The possibility of losing the find to his rival finally got Marsh’s attention. Marsh quickly wrote a “Notice of a New and Gigantic Dinosaur” for the July issue of the American Journal of Science, in which he said the new dinosaur “surpassed in magnitude any land animal hitherto discovered.” He hired Lakes as a bone collector and dispatched one of his lead collectors, Benjamin Franklin Mudge, to work with Lakes at the Morrison site. By the middle of July the pair had another 2,500 pounds of rocks and bones ready to ship. Along with a nearly simultaneous discovery of big bones at Como Bluff, Wyoming, the excavations at Dinosaur Ridge marked the start of what has been called the “dinosaur rush” in America.
Lakes continued to collect bones for Marsh on Dinosaur Ridge until 1879, when he closed his quarries. The new dinosaur genera discovered at Dinosaur Ridge during these years included Allosaurus, Apatosaurus, Diplodocus, and Stegosaurus, the latter of which is now the state fossil of Colorado. In addition, the rock layer in which Lakes made his discoveries was named the Morrison Formation after the town of Morrison.
Dinosaur Track Discoveries: Alameda Parkway, 1937
Alameda Parkway was extended over Dinosaur Ridge to Red Rocks when the Red Rocks Amphitheatre was under construction in the late 1930s. Construction exposed rock layers that had previously been hidden or difficult to access. In 1937 workers discovered dinosaur tracks in rock layers from the Dakota Group on the east side of the ridge. New excavations and maps of the tracks in 1992–93 revealed a total of 335 tracks and 37 trackways. Ten different rock strata contain tracks, with at least 78 individual dinosaurs represented in tracks preserved on the ridge.
The tracks found in the Dakota Group originated 50 million years later than the fossils found in the Morrison Formation. As a result, they represent different dinosaurs. There were few known fossilized bones from this period until recently, so the tracks, which provide evidence about movement and behavior, have played a large role in the way paleontologists understand these dinosaurs.
The tracks on Dinosaur Ridge primarily record the activity of Iguanadon-like herbivores and ostrich-sized carnivores. The herbivores walked on all fours at about two miles per hour, and evidence of parallel tracks indicates that they traveled in groups. The carnivore tracks, which are about nine inches long, reveal animals that weighed 100 pounds and walked upright on two legs at a speed of five miles per hour. They traveled alone. All these tracks were made about 100 million years ago, when the dinosaurs were migrating north and south on the “Dinosaur Freeway” along the shore of the ancient inland sea.
The nonprofit Friends of Dinosaur Ridge was formed in 1989 to help preserve the site and educate visitors. The group operates a visitor center on the east side of the ridge as well as a newer Discovery Center, which opened in 2014, on the west side of the ridge. The group also maintains West Alameda Parkway over the ridge, which is now closed to vehicle traffic, and has erected a series of interpretive signs to help visitors understand the ridge’s many tracks, bones, and geological features. On the west side of the ridge, Alameda Parkway passes near one of Lakes’s original bone quarries—Quarry #5. In 1995 Friends of Dinosaur Ridge constructed a pedestrian ramp that enables visitors to see the fossils still entombed in rock at the quarry site.
Lakes’s original quarries on Dinosaur Ridge were closed in 1879, his last year of hunting for fossils on the ridge, and they remained largely dormant for more than 120 years. In the early twenty-first century, researchers at the Morrison Natural History Museum rediscovered one of the quarries and began to examine it again. In 2003 they found the first Stegosaurus footprints ever discovered in Colorado, and in 2006 they made the first discovery in the world of baby Stegosaurus tracks. In early 2016, University of Colorado–Denver geologist Martin Lockley found two-toed raptor tracks on Dinosaur Ridge. The 105-million-year-old tracks were the first two-toed tracks discovered in Colorado and the second ever found in North America.
Dinosaur Ridge has been recognized multiple times at the federal and state levels as a site with significant historical and scientific value. It has been designated by the National Park Service as a National Natural Landmark (1973), by the state of Colorado as a State Natural Area (2001), and by the Colorado Geological Survey as a Point of Geological Interest (2006). In addition, much of the ridge lies within Jefferson County’s Open Space system.