The Morrison Formation
A single American rock unit yields more giant dinosaurs than anywhere else on Earth.
- When
- —
- Duration
- 7 million years
- Known to
- ± 2 million years
- Era
- Jurassic, Mesozoic
Deposited between roughly 155 and 148 million years ago across the western United States, the Morrison Formation preserves floodplains and river channels crowded with dinosaurs — thirteen genera of sauropods alone, plus Allosaurus, Stegosaurus and Ceratosaurus. It has been quarried since the 1870s, fuelled the Bone Wars between Marsh and Cope, and supplies the animals in most museum halls worldwide.