The Gettysburg Formation is conformably underlain by the New Oxford Formation, which is the basal unit of the Newark Supergroup in south-central Pennsylvania.
The Gettysburg is mapped from the Maryland border through Adams, Cumberland, Lancaster, and York Counties to the southern borders of Dauphin and Lebanon Counties.
In these counties and to the north the rock unit is called the Hammer Creek Formation.

The Gettysburg Formation is divided into several members.
The upper part is sometimes referred to as the Conewago conglomerate, and the Conewago Mountains in York County are underlain by it.
The Heidlersburg Member, in the middle of the formation, is "red, green, and gray shale and argillite and minor gray to white sandstone".
The Gettysburg Formation is conformably underlain by the New Oxford Formation, which is the basal unit of the Newark Supergroup in south-central Pennsylvania. The Gettysburg is mapped from the Maryland border through Adams, Cumberland, Lancaster, and York Counties to the southern borders of Dauphin and Lebanon Counties. In these counties and to the north the rock unit is called the Hammer Creek Formation.
The Gettysburg Formation is divided into several members. The upper part is sometimes referred to as the Conewago conglomerate, and the Conewago Mountains in York County are underlain by it. The Heidlersburg Member, in the middle of the formation, is "red, green, and gray shale and argillite and minor gray to white sandstone".
Gettysburg Formation