Monongahela Formation

The Monongahela Formation is a geologic formation in West Virginia, Pennsylvania, Ohio, and Maryland. It is dated to the Carboniferous period. The top of the group is marked by the Waynesburg Coal (No. 11 Coal) and its base is marked by the Pittsburgh coal seam (No. 8 Coal). The Pittsburgh coal is the thickest and most extensive (11,000 sq mi) bituminous coal bed in the Appalachian Basin