Pennsylvania has a great diversity of bedrock that is at or near the surface.

In the southeastern part of the state, there are crystalline (igneous and metamorphic) rocks. They are bordered to the northwest by a 3- to 20-mile-wide band of mostly red sedimentary rocks having multiple intrusions of the igneous rock diabase. This band arcs from Adams County to Bucks County. The remainder of the state is underlain by sedimentary rocks of practically all types.

Pennsylvania Geological Survey staff compiled 19 different groups of rock types and published them on the statewide Map 63, Rock Types of Pennsylvania (ZIP). Descriptions of the most common rock types can be found in the booklet ES 1, Rocks and Minerals of Pennsylvania (PDF), and more detailed descriptions are given for named rock units in the report EG 1, Engineering Characteristics of the Rocks of Pennsylvania (ZIP).

The list of counties below link to PDF files of corresponding county rock-type maps. Each county map has been scaled to fit on letter-size paper. The rock-type data were extracted from Map 63 and are represented by numbers and colors on top of a shaded-relief base map. Major highways and municipalities aid with location.

These are regional maps that indicate broad trends and patterns. They should not be used for detailed analysis or site-specific applications (e.g., permitting).