Fossil Atlas formation guide
The Morrison Formation is one of North America's classic dinosaur-bearing rock units. Spanning the Late Jurassic, it has yielded Stegosaurus, Allosaurus, Diplodocus, Brachiosaurus, and many of the animals people associate with the Bone Wars era.
Geology
The Morrison consists of sandstone, mudstone, and limestone deposited by rivers, lakes, and wind across a broad basin. Seasonal flooding concentrated bones in channel deposits — the classic dinosaur quarries. The formation is remarkable for its sheer geographical extent (over 1.5 million square kilometers) and the consistency of its fossil fauna across that enormous area.
The Bone Wars
The Morrison was the battlefield for the most intense rivalry in the history of science. Marsh and Cope's teams raced to discover and name new dinosaurs from Morrison quarries. The competition was ruthless — involving bribery, dynamited sites, and personal attacks — but it produced lasting science: Stegosaurus, Allosaurus, Diplodocus, Apatosaurus, Camarasaurus, and dozens more. Every major museum still displays Morrison dinosaurs.
Fossil Atlas
The Fossil Atlas Morrison Formation hotspot maps selected records from the current site dataset. Stegosaurus currently has a full specimen profile on the site. As the dataset grows, additional Morrison taxa such as Allosaurus, Diplodocus, and Apatosaurus may receive individual profiles.
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FAQ
The Morrison Formation spans the Late Jurassic, roughly 155–145 million years ago (Kimmeridgian to Tithonian stages). This places it about 80–90 million years before the end-Cretaceous extinction that killed T. rex and Triceratops. The Morrison was deposited over approximately 10 million years in a broad, low-lying basin east of a rising mountain range that would eventually become the modern Rockies.
The Morrison Formation is exposed across a vast swath of the western United States, from Montana in the north to New Mexico in the south, and from Utah in the west to the Black Hills of South Dakota in the east. Classic fossil localities include Como Bluff (Wyoming), Garden Park (Colorado), Dinosaur National Monument (Utah/Colorado), the Cleveland-Lloyd Dinosaur Quarry (Utah), and the Black Hills region. These sites have produced thousands of dinosaur bones over more than 140 years of collecting.
The Morrison was deposited in a semi-arid to seasonally wet environment crossed by river channels and dotted with shallow lakes. During the wet season, rivers carried sand and gravel; during dry seasons, fine mud accumulated on floodplains. The famous dinosaur quarries often represent ancient river channel deposits where floods concentrated bones from animals that died upstream. Plant fossils — ferns, cycads, ginkgoes, and conifers — suggest a landscape of open woodlands and fern prairies rather than dense forest.
The Morrison is one of the classic dinosaur-bearing formations of western North America and was central to the Bone Wars of the late 19th century. Its fauna includes sauropods such as Diplodocus and Brachiosaurus, theropods such as Allosaurus, and the armored Stegosaurus. Fossil Atlas currently gives Stegosaurus the strongest linked profile while treating the broader Morrison fauna as formation context.
Sources
Source links show where Fossil Atlas gets record and curation context. They do not make this page an exhaustive scientific bibliography.
Caveat
This page summarizes the Morrison Formation based on published literature and the current Fossil Atlas dataset. Formation descriptions and age ranges are approximate. The dinosaur list highlights major taxa; it is not comprehensive for all Morrison dinosaur species.
Fossil maps on linked pages show modern discovery locations for selected records. These are not ancient habitat or range maps.