The Allegheny Formation makes up the base of the three local formations. It can be found along the Kiskiminetas River. The two defining characteristics of the formation are the Upper Freeport sandstone and shale, and the Upper Freeport coal bed. Mining of the Upper Freeport Coal is one of the reasons for mine subsidence locally. It is one of the largest coal seams locally.

Examples of Upper Freeport Sandstone along PA 66, a half mile from Parks Township.

Formation Stratigraphy

Allegheny Formation

The Upper Freeport coal bed marks the youngest part of the formation. The upper and lower Freeport Coal both have been mined quite extensively in Parks Township. However, it’s not a highly profitable coal seam. It is quite narrow compared to other extensive coal stratums. In the 1933 Hughes report of the Freeport Quadrangle, Hughes noted several mining operations in local towns, but at a lower number compared to the past. Fast forward to today, they are nearly non-existent. The only mining company that I know of locally is the Rosebud mining company in nearby Kittanning.

The massive Upper Freeport sandstone and shale is quite easy to recognize, with huge facades of sandstone rock tens of feet tall in areas. As you travel along PA Route 66 along the Kiskiminetas river, some cut exposures are easy to see. There are large exposures elsewhere, along PA. 66 in Westmoreland County, right after crossing the Apollo Bridge.

Formations Above the Allegheny Formation

Above the formation sits the entire Conemaugh Group. The group divides into two formations, the Glenshaw Formation directly above the Allegheny, and the Casselman Formation above the Glenshaw.

More about the Allegheny Formation Online


  • Hughes, H.H, 1933, No. 36 Freeport Quadrangle, Topographical and Geologic Atlas of Pennsylvania