Map Layers

Click on the map of Pennsylvania for rock unit information. 

This map indicates formations that may have acid-forming minerals, primarily pyrite. Although this map is useful for general planning and preliminary site studies, it does not substitute for site-specific subsurface investigations of the rock units that will be disturbed through excavation, mining, or drilling. The map indicates geologic units and points that may have the potential to generate acid drainage (AD). It of course does not guarantee that AD will occur or conversely, that AD cannot occur in other areas and formations not shown on this map. The occurrence of AD, therefore, is not restricted to the areas delineated on the map.

Bedrock geology units are based on digital compilations by Miles and Whitfield, 2001 (see map text for references). Map rock formation color does not imply “risk” or potential of acid drainage, but only represents different geologic units.

Unit 1

Conemaugh Group. Includes the Casselman and Glenshaw Formations, and the Conemaugh Formation of the Broadtop coal region in northeastern Bedford and southern Huntingdon Counties. Although typically not as problematic as other coal-bearing units, the Conemaugh can produce acid drainage.

Unit 2

Monongahela Group and Waynesburg Formation. Includes known problematic coals such as the Pittsburgh and Waynesburg coals (and underclays), and the Sewickley coals, which can also have acidic drainage. 

Unit 3

Allegheny Formation. Includes problematic coals such as the Clarion, Lower Kittanning, and Middle Kittanning coals. Fewer problems occur with the Upper Kittanning and Freeport coals.

Unit 4

Pottsville Formation, in western Pennsylvania, and Pottsville and Allegheny Formations, undivided, in north-central Pennsylvania. Especially east and southeast of the plateau along the Allegheny Front; includes the Mercer coals, which can be problematic. Calcareous minerals are rare in the Pottsville.

Unit 5

Burgoon Formation, in north-central Pennsylvania and along the Allegheny Front.

Unit 6

The Tuscarora Formation in Huntingdon, Bedford, Blair, and Centre Counties, and in the Metal Township area, Franklin County.

Unit 7

The Bald Eagle Formation along Bald Eagle ridge in Centre County

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Unit 8

The top of Ridgeley Formation through base of Marcellus Formation (including the Onondaga Formation). Map units shown are the Ridgeley member of the Old Port Formation, Onondaga Formation, Onondaga and Old Port Formations, undivided, and the Hamilton Group, but only the top of the Ridgeley and the base of the Marcellus are targets.

Unit 9

The anthracite coal fields in eastern Pennsylvania (includes the Pottsville and Llewellyn Formations).

Unit 10

In the Carbon and Monroe Counties area, the top of Palmerton Sandstone through base of Marcellus Formation, Carbon County. Map units include Buttermilk Falls Limestone through Esopus Formation, undivided, and the Marcellus Formation, but only the top of Palmerton Sandstone and the base of Marcellus Formation are targets.

Unit 11

The base of Hardyston Formation in Lehigh County. All of the Hardyston Formation in Lehigh County is shown.

Unit 12

The Pickering Gneiss. Map unit is the graphitic felsic gneiss.

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The map also includes these other layers:

  • Areas declared by the Pennsylvania Department of Environmental Protection (DEP) to be unsuitable for mining because of the potential for abandoned mine drainage
  • Streams affected by abandoned mine drainage due to pH and metals
  • Streams impaired by abandoned mine drainage from 1998 to 2004 with problems listed as including pH and/or metals, DEP, 2004
  • Point locations of potentially significant sulfide mineralization based on published and unpublished information, Pennsylvania Geological Survey
  • Preliminary landform subdivisions of Pennsylvania
  • Late Wisconsinan glacial border


Original map scale is 1:500,000. The map is not intended to be used for detailed or site-specific analyses, nor is it intended to be used at any scale finer than 1:250,000 (for example, use at 1:24,000 or 1:100,00 scales is inappropriate).