| St. Marys Formation | |
|---|---|
| Stratigraphic range: Neogene | |
| Type | Formation |
| Unit of | Chesapeake Group |
| Underlies | Eastover Formation |
| Overlies | Choptank Formation |
| Location | |
| Region |  Maryland Virginia |
| Country |  United States |
The St. Marys Formation is a geologic formation in Maryland and Virginia, United States. It preserves fossils dating back to the Miocene Epoch of the Neogene period. It is the youngest Miocene formation present in the Calvert Cliffs and is part of the Chesapeake Group.