Soon, other exposures of the Morrison Formation were producing dinosaur fossils, some of them quite remarkable for their size, abundance, and state of preservation. 1877 turned out to be the watershed year of discovery. World-class finds of dinosaur bones were made in four separate locations in Colorado and Wyoming that year. The first discovery took place just east of Morrison, Colorado on what is now known as Dinosaur Ridge. (This section of the Morrison Formation represents the type locality for the unit. The formal name of the formation was taken from the town closest to the type locality.) The next discovery took place south of Denver, near Canon City. At a location known as Garden Park, a rich bone-bearing layer was discovered by O.W. Lucas. Then, in Wyoming, another report of a dinosaur "graveyard" surfaced. Extending for 7 miles along the Union Pacific Railroad, a vast deposit of dinosaur bones was exposed at the surface. Known as Como Bluff, the location would prove to be a fountainhead of dinosaur bones. Finally, another Morrison boneyard was discovered just northwest of Como Bluff. Here, the bones were literally scattered along the surface! They were so abundant that a local sheepherder had built a cabin out of them, giving the location its name: the Bone Cabin Quarry.
That brings us to the summer of 1909 and the fossil discoveries of Earl Douglass. An employee of the Carnegie Museum, Douglass was exploring the Echo Park area of northwestern Colorado when he made the find of a lifetime. Lying at his feet that hot August day was a spectacular dinosaur burial ground that would soon come to be called the "Dinosaur Quarry". Locked within a sandstone lens nearly 50 feet thick was a fossil "hash" of dinosaur remains, the like of which had never been seen before! Earl Douglass was hooked. He would spend the rest of his life searching for bones in the "Dinosaur Quarry". The importance of the site was not unappreciated. In 1915, the fossil beds were officially designated as Dinosaur National Monument. Initially consisting of only 80 acres, it was greatly enlarged in 1938 to include the Split Mountain area, Rainbow Park, Lodore Canyon, Echo Park, Jones Hole, Blue Mountain, and Deerlodge Park. It now encompasses over 325 square miles of rugged, fossil-bearing terrain.
When Earl Douglass discovered an articulated "Brontosaurus" skeleton (later to be renamed Apatosaurus) in the Morrison Formation near Echo Park, he had no idea that over 5000 dinosaur bones would eventually be recovered from the area he was working. Nine species of dinosaur have been found in the "Dinosaur Quarry", including carnivorous therapods (like Allosaurus), plant-eating ornithiscians (like Stegosaurus), and gigantic sauropods (like Diplodocus). Of these, the sauropods dominate. Indeed, nearly 75% of all the dinosaur bones recovered from the "Dinosaur Quarry" are from these massive herbivores.
Both orders of dinosaurs are represented at the "Dinosaur Quarry" in Dinosaur National Monument. These include the older, more primitive lizard-hipped sauriscians and the more advanced bird-hipped dinosaurs known as the ornithiscians. As mentioned above, the sauropods are by far the most abundant type of dinosaur found in the quarry. Douglass's Apatosaurus was one of the largest, weighing in at 35 tons when fully grown. Another giant sauropod found in the quarry is the famous dinosaur known as Diplodocus. Growing up to 90 feet in length, Diplodocus is the longest dinosaur that has ever been discovered. Two other large sauropods have left their remains in the mudstones of the Morrison Formation near Echo Park. Camarasaurus and Barosaurus have both been found here, although their skulls have yet to turn up. (Curiously, sauropod skulls are extremely rare in the fossil record. In some cases, it is the only part of the skeleton that is missing! It may be that their fragile nature keeps them from being preserved, or that predators and scavengers preferentially consumed the skulls first.)
Predatory dinosaurs are also well represented at Dinosaur National Monument. These include the famous carnivore known as Allosaurus and the horned therapod Ceratosaurus. Allosaurus was quite literally the terror of the Jurassic. Growing up to 35 feet in length and weighing up to 2½ tons, Allosaurus was the top predator of its time.
Three other species of dinosaur have turned up in the quarry at Dinosaur National Monument. Two of them are plant-eating beaked dinosaurs while the third is the famous plated dinosaur known as Stegosaurus. First discovered near Morrison, Colorado, Stegosaurus is fairly common in the fossil deposits at Echo Park. Second in abundance only to the sauropods, Stegosaurus grew up to 25 feet in length and weighed up to 5 tons. It was an imposing opponent for Allosaurus. The remaining two dinosaur species both possessed a horny beak that was used to process vegetation. Camptosaurus was an early ancestor of the iguanodons while Dryosaurus was a more evolved ornithiscian that probably moved in herds for protection.
An absolute wonder of the scientific world, Dinosaur National Monument is a microcosm of ancient Jurassic life in North America. From the muds, silts, and sands of the Morrison Formation, a host of dinosaur bones has poured forth, revealing a world dominated by giant reptiles. Our understanding of this ancient world and the dinosaurs that inhabited it would not have been possible if it weren't for the modest collection of mudstones that we call the Morrison Formation.