| Martinsburg Formation | |
|---|---|
| Stratigraphic range: Late Ordovician | |
 A sample of the Martinsburg shale from the Pennsylvania Turnpike (Northeast Extension) at mile post 66. | |
| Type | Formation |
| Underlies | Juniata Formation |
| Overlies | Jacksonburg Limestone and Utica Shale |
| Location | |
| Region | Virginia[1] and West Virginia |
| Country | United States |
The Ordovician Martinsburg Formation (Om) is a mapped bedrock unit in Pennsylvania, New Jersey, Maryland, Virginia, and West Virginia. It is named for the town of Martinsburg, West Virginia for which it was first described. It is the dominant rock formation of the Great Appalachian Valley in New Jersey (where it is called Kittatinny Valley) and Pennsylvania (in the Lehigh Valley and Lebanon Valley).