Montana, North Dakota, South Dakota, Wyoming, United States
Hell Creek preserves the last two million years of the dinosaur age — the final chapter before the Chicxulub impact — and has produced the most complete skeletons of Tyrannosaurus rex, Triceratops, and Ankylosaurus ever found. It is the world's primary window into end-Cretaceous ecosystems and the mass extinction event itself. The K-Pg boundary layer marking the asteroid impact is clearly visible within Hell Creek outcrops.
Deposited by river systems draining an ancient Rocky Mountain range, the formation consists of alternating sandstone channel fills and grey mudstone floodplain deposits. The fine-grained floodplain sediments were ideal for rapid burial and bone preservation. The presence of the iridium anomaly — a worldwide chemical signature of the Chicxulub impact — at the top of the formation makes Hell Creek uniquely important for studying the extinction.
Barnum Brown of the American Museum of Natural History discovered the first T. rex specimen in Hell Creek outcrops in 1902, sparking over a century of intensive collecting. Sue (FMNH PR 2081), the largest and most complete T. rex, was found in South Dakota in 1990 and auctioned for $8.36 million in 1997. Today the formation remains one of the most actively excavated in North America.
The iridium layer marking the asteroid impact that ended the dinosaurs is physically visible in Hell Creek exposures — you can put your finger on the exact moment.
Over 50 individual T. rex specimens have been catalogued from Hell Creek and related rocks — more than any other large theropod.
The last non-avian dinosaurs on Earth almost certainly walked across what is now Montana and the Dakotas.
Hell Creek's rocks were deposited so close to the extinction event that researchers have searched the sediments for evidence of the actual days and weeks after the impact.
4 species in our database · sorted by size