| Hailey Shales Formation | |
|---|---|
| Stratigraphic range: Cretaceous | |
| Type | Formation | 
| Location | |
| Region | Wyoming | 
| Country | United States | 
The Hailey Shales Formation is a geologic formation in Wyoming. It preserves fossils dating back to the Cretaceous period.Plesiopleurodon was found in this formation.