Morrison Formation
Late Jurassic (155-148 million years ago)
Morrison Formation
The Morrison Formation is the single most important dinosaur-bearing rock unit in North America and arguably the world. Spanning vast stretches of the Western Interior from Montana to New Mexico, this Late Jurassic formation has produced the iconic dinosaurs that define the era in the public imagination: Diplodocus, Stegosaurus, Allosaurus, Apatosaurus, and Brachiosaurus, among dozens of others. More than 150 years after its discovery, the Morrison continues to yield new species and new insights into Jurassic ecosystems.
Geological Context
The Morrison Formation was deposited approximately 155 to 148 million years ago during the Late Jurassic Period. At that time, the western interior of North America was a broad, semi-arid to seasonally wet floodplain dotted with rivers, lakes, and seasonal ponds. The ancestral Rocky Mountains had not yet risen to their modern heights, and a shallow seaway periodically encroached from the north.
The formation consists primarily of:
- Mudstone and claystone (often brightly colored in greens, reds, and grays) representing floodplain deposits
- Sandstone channels representing ancient river and stream beds
- Limestone and marl representing lake deposits
- Conglomerate lenses representing high-energy stream deposits
The formation’s thickness varies from less than 100 feet to over 900 feet, depending on location. It is typically exposed in badlands, cliff faces, river cuts, and road cuts across the western states.
The Morrison Formation overlies the marine Sundance Formation (or equivalent units) and is overlain by the Early Cretaceous Burro Canyon Formation or Cedar Mountain Formation, depending on location. This stratigraphic position --- sandwiched between marine and early Cretaceous deposits --- makes it readily identifiable in the field by its characteristic colorful mudstones.
The Bone Wars: Cope vs. Marsh
The Morrison Formation was the primary battlefield of the most famous rivalry in the history of paleontology: the Bone Wars between Edward Drinker Cope and Othniel Charles Marsh.
Beginning in the late 1870s, these two wealthy and ambitious paleontologists launched competing expeditions into Morrison Formation exposures across Colorado, Wyoming, and beyond. Their rivalry was intense, petty, and spectacularly productive:
- Marsh operated primarily through Yale’s Peabody Museum. His field crews worked sites at Como Bluff, Wyoming, and several Colorado localities. Marsh named Allosaurus, Apatosaurus, Diplodocus, Stegosaurus, and Triceratops (the latter from a different formation), among many others.
- Cope worked with the Academy of Natural Sciences in Philadelphia. His crews competed directly with Marsh’s teams, sometimes at adjacent sites. Cope named Camarasaurus, Coelophysis (from a different formation), and dozens of other species.
The two men resorted to espionage, bribery, theft, and even deliberate destruction of fossils to prevent the other from studying them. They published hasty, error-filled descriptions in a race to name species first, leading to decades of taxonomic confusion (the Brontosaurus/Apatosaurus debate is a direct legacy of this rivalry).
Despite the dysfunction, the Bone Wars transformed American paleontology. Between them, Cope and Marsh named over 130 new dinosaur species (many later synonymized) and established the Morrison Formation as the world’s premier Jurassic dinosaur deposit. Their collections remain the foundation of major museum exhibits across the country.
Key Localities
Dinosaur National Monument (Utah/Colorado Border)
The most famous Morrison Formation locality in the world. In 1909, Earl Douglass of the Carnegie Museum discovered a massive concentration of Jurassic dinosaur bones in a sandstone ledge near Vernal, Utah. The site eventually yielded over 1,500 bones visible in a single rock face, now enclosed within the Quarry Exhibit Hall. Dinosaurs recovered include Allosaurus, Diplodocus, Apatosaurus, Camarasaurus, Stegosaurus, and Dryosaurus. The site is now a National Monument and open to the public year-round. No collecting is permitted.
Garden Park, Colorado
Located near Canon City, Colorado, Garden Park was one of the original Bone Wars battlegrounds. Cope’s crews worked this area extensively in the 1870s and 1880s, recovering some of the first Camarasaurus and other Morrison dinosaurs. The area continues to produce important specimens. Garden Park is on a mix of BLM and private land; BLM portions require permits for vertebrate fossil collection.
Como Bluff, Wyoming
This long ridge near Medicine Bow, Wyoming, was Marsh’s primary Morrison Formation quarry site during the Bone Wars. Como Bluff produced many of Marsh’s most famous specimens, including the type specimens of Apatosaurus and Allosaurus. The site is on a mix of private and public land. A small cabin built entirely from dinosaur bones (a historical curiosity, not a paleontological practice anyone endorses today) sits along the highway nearby.
Cleveland-Lloyd Dinosaur Quarry, Utah
Located south of Price, Utah, this BLM-managed site is unusual for its extraordinary concentration of Allosaurus fossils --- over 40 individuals have been recovered, representing roughly 70% of the bones found at the site. The reason for this concentration is debated; hypotheses include a predator trap (like a Jurassic tar pit), a drought-related mass death, or a poisoned water source. The quarry has a visitor center and is open seasonally. Vertebrate fossil collecting is prohibited.
Dry Mesa Quarry, Colorado
Near Delta, Colorado, this site produced some of the largest Morrison Formation dinosaurs, including Supersaurus, one of the longest dinosaurs known (over 100 feet). The quarry was worked extensively by Brigham Young University teams in the 1970s and 1980s.
Howe Quarry, Wyoming
Near Shell, Wyoming, rancher Barker Howe discovered a massive bone bed in 1934 that was excavated by Barnum Brown of the American Museum of Natural History. The Howe Quarry produced an extraordinary concentration of sauropod bones, including Diplodocus, Apatosaurus, and Barosaurus. Nearby sites (Howe-Stephens Quarry and Howe-Scott Quarry) have produced additional important specimens in recent decades.
Fruita Paleontological Area, Colorado
Near Fruita, Colorado, this BLM-managed site has produced exceptionally well-preserved small dinosaurs, mammals, and other vertebrates from the Morrison Formation. The tiny mammal Fruitafossor is named for this locality. The site provides an important window into the small-animal ecosystem that lived alongside the giant sauropods.
What the Morrison Formation Tells Us
The Morrison Formation preserves one of the best-documented terrestrial ecosystems of the Mesozoic. The dinosaur fauna is dominated by:
- Sauropods (long-necked herbivores): Diplodocus, Apatosaurus, Brachiosaurus, Camarasaurus, Barosaurus, and Haplocanthosaurus were all present, sometimes in the same ecosystem. How so many giant herbivores coexisted is an active area of research; differences in head height, tooth shape, and feeding strategy likely allowed niche partitioning.
- Theropods (predators): Allosaurus was the dominant large predator. Ceratosaurus, Torvosaurus, and Marshosaurus were also present. Smaller theropods included Ornitholestes and Coelurus.
- Ornithischians: Stegosaurus is the most famous, with its distinctive plate-and-spike arrangement. Camptosaurus (an early ornithopod), Dryosaurus, and Gargoyleosaurus (an early ankylosaur) round out the herbivore guild.
Beyond dinosaurs, the Morrison preserves crocodylomorphs, turtles, pterosaurs, lungfish, freshwater clams, snails, and a diverse array of tiny mammals. Plant fossils include conifers, ferns, cycads, and ginkgoes --- there were no flowering plants yet.
What Amateurs Can Find on BLM Land
Large portions of the Morrison Formation are exposed on BLM (Bureau of Land Management) land across the western states. The rules for amateur collecting on BLM land are clear:
What You CAN Collect (No Permit Needed)
- Invertebrate fossils: Freshwater clams (unionids), snails (gastropods), and ostracods are common in Morrison lake and river deposits. These are legal to casually collect in reasonable quantities for personal use.
- Plant fossils: Fossilized wood (including petrified wood), leaf impressions, and other plant material can be collected. Note that petrified wood collection on BLM land is limited to 25 pounds per day plus one piece, up to 250 pounds per year.
- Trace fossils: Invertebrate burrows and other non-vertebrate trace fossils.
What You CANNOT Collect (Permit Required)
- Any vertebrate fossil: Dinosaur bone, teeth, tracks, crocodile remains, turtle shells, fish bones, and mammal fossils all require a paleontological research permit. This applies even to small, fragmentary, and seemingly insignificant pieces.
- The permit requirement is absolute. There is no de minimis exception. A single fragment of dinosaur bone collected from BLM land without a permit is a federal violation.
Practical Advice
If you’re exploring Morrison Formation exposures on BLM land, you will likely encounter vertebrate fossil material --- it’s common in many areas. If you find dinosaur bone or other vertebrate material:
- Leave it in place
- Photograph it with a scale object and record GPS coordinates
- Report it to the local BLM field office
- Feel good about contributing to science --- many important discoveries have been made by hikers and amateur naturalists who reported finds to authorities
If you want to collect Morrison Formation dinosaur material legally, your best option is to work with a commercial dig program that operates on private land, or to obtain written permission from a private landowner whose property exposes Morrison rocks.
Visiting Morrison Formation Sites
Several Morrison Formation sites are open to the public:
- Dinosaur National Monument (Jensen, Utah) --- The Quarry Exhibit Hall is a must-see. Open year-round, though some areas close seasonally.
- Dinosaur Ridge (Morrison, Colorado) --- The type locality for the formation. Guided tours of the Morrison Formation bone layer and Cretaceous trackways. Just west of Denver.
- Cleveland-Lloyd Dinosaur Quarry (Price, Utah) --- BLM visitor center open seasonally (typically spring through fall).
- Garden Park Fossil Area (Canon City, Colorado) --- Self-guided trails through Bone Wars-era quarry sites.
- Red Gulch Dinosaur Tracksite (Shell, Wyoming) --- Middle Jurassic tracks near Morrison Formation exposures.
The Morrison Formation is 155 million years old, and it’s still producing discoveries. Every rainstorm, every freeze-thaw cycle, every spring snowmelt exposes new bone. The formation that fueled the Bone Wars is far from exhausted, and its next great discovery could be made by anyone paying attention to the colorful mudstones of the Jurassic West.