Geological Formations
Understanding geological formations is the key to finding fossils. Each formation represents a specific time period, environment, and set of organisms. Learn what to expect from the most productive formations in the US.
Green River Formation
Eocene (53-48 million years ago)
Home to the world's most perfectly preserved fossil fish. An ancient lake system that captured an extraordinary snapshot of Eocene life in exquisite detail.
Hell Creek Formation
Late Cretaceous (68-66 million years ago)
The world's most famous dinosaur-bearing formation, preserving the final chapter of the Age of Dinosaurs. Home to T. rex, Triceratops, and the K-Pg extinction boundary.
Morrison Formation
Late Jurassic (155-148 million years ago)
A comprehensive guide to the Morrison Formation, the most productive Late Jurassic dinosaur-bearing rock unit in the world, covering its geology, key fossil localities, the Bone Wars, and what collectors can find today.