Hell Creek Formation

Fossil Sites

Fossils of the Hell Creek Formation

Geologic Time: Cretaceous, some 70 million years ago

Related Interest: Fox Hills Formation


Hell Creek Formation where T-Rex was foundThe Hell Creek Formation is one of the more famous and intensely studied dinosaur fossil sites. Hell Creek is expansive, and includes areas of Eastern Montana badlands, Northwestern South Dakota, and Southwestern North Dakota. The strata’s age ranges from about 65 to 70 million years old, and were formed in a delta with a warm and moist climate. Interestingly, the famous iridium enriched K-T boundary layer that separates the Mesozoic from the Cenozoic occurs as thin, discontinuous but distinct bedding plane near the top of the Formation.

The Hell Creek Formation biota is most famous for its dinosaurs, most complete Hadrosaurid dinosaur ever found, but is otherwise huge and diverse, encompassing plants, invertebrates, fish, reptiles, and amphibians, and mammals. Bird (avian dinosaurs) and pterosaur fossils have also been found, as well as the teeth of sharks that were apparently tolerant to fresh water.

The following dinosaurs and types have been discovered from Hell Creek: Tyrannosaurus rex; Nanotyrannus lancensis; Troodon formosus; Dromaeosaurid; Ornithomimus; Nodosaurids; Edmontonia; Denversaurus schlessmani; Thescelosaurus; neglectus; Thescelosaurus sp.; Edmontosaurus regalis; Edmontosaurus annectens; Anatotitan copei; Pachycephalosaurids, Pachycephalosaurus wyomingensis, Ceratopsids; Triceratops horridus; and Torosaurus latus.

Hell Creek Fossils

Also see: North Dakota Stratigraphy