Geologic units in Allegheny county, Pennsylvania

Casselman Formation (Pennsylvanian) at surface, covers 45 % of this area

Cyclic sequences of shale, siltstone, sandstone, red beds, thin, impure limestone, and thin, nonpersistent coal; red beds are associated with landslides; base is at top of Ames limestone.

Monongahela Group (Pennsylvanian) at surface, covers 26 % of this area

Cyclic sequences of limestone, shale, sandstone, and coal; commercial coals present; base is at bottom of Pittsburgh coal.

Glenshaw Formation (Pennsylvanian) at surface, covers 25 % of this area

Cyclic sequences of shale, sandstone, red beds, and thin limestone and coal; includes four marine limestone or shale horizons; red beds are involved in landslides; base is at top of Upper Freeport coal.

Waynesburg Formation (Permian and Pennsylvanian) at surface, covers 3 % of this area

Cyclic sequences of sandstone, shale, limestone, and coal; commercial coals present; base is at bottom of Waynesburg coal.

Allegheny Formation (Pennsylvanian) at surface, covers 0.7 % of this area

Cyclic sequences of sandstone, shale, limestone, clay, and coal; includes valuable clay deposits and Vanport Limestone; commercially valuable Freeport, Kittanning, and Brookville-Clarion coals present; base is at bottom of Brookville-Clarion coal.

Washington Formation (Permian) at surface, covers < 0.1 % of this area

Cyclic sequences of sandstone, shale, limestone, and coal; includes some red shale; base is at bottom of Washington coal.