Geology and Stratigraphy of the Eastern Rivers and Mountains
The Eastern Rivers and Mountains Network (ERMN) consists of nine NPS units in West Virginia, Pennsylvania, western New Jersey, and western New York. The parks include: Allegheny Portage Railroad National Historic Site (ALPO), Bluestone National Scenic River (BLUE), Delaware Water Gap National Recreation Area (DEWA), Fort Necessity National Battlefield (FONE), Friendship Hill National Historic Site (FRHI), Gauley River National Recreation Area (GARI), Johnstown Flood National Memorial (JOFL), New River Gorge National Park and Preserve (NERI), and Upper Delaware Scenic and Recreational River (UPDE).The network parks are dominated by eastern deciduous forests and river systems within temperate latitudes of the central Appalachian Mountains. The parks are situated within broad river floodplains to small, ephemeral streams, high mountains to deep gorges, and dry barrens to mesic forests (Marshall and Piekielek 2004). Five parks are dominated by large rivers (NERI, GARI, BLUE, DEWA and UPDE), three of which contain river sections that have Wild and Scenic River designation (BLUE, UPDE, DEWA). Collectively the parks of the ERMN preserve important fauna, flora, habitat, rivers, and recreational resources.
A Brief Geologic History—Eastern Rivers and Mountains Network
A few examples of events and Network resources in each geologic time period are highlighted below, from youngest to oldest.
No Cenozoic units are mapped within the ERMN parks.
No Mesozoic units are mapped within the ERMN parks.
All of the geologic strata mapped within the parks of the ERMN are Paleozoic in age (see Geologic Time Scale). The oldest geologic formation within the network is the Late Ordovician Martinsburg Formation exposed at DEWA, which is the only park in which pre-Devonian rocks are mapped. Six formations at DEWA also span the Silurian. Devonian strata occur in three parks including ALPO, DEWA and UPDE, with the widespread Catskill Formation mapped in all three of these parks. Mississippian-age units occur within ALPO, BLUE, FONE, and NERI. Pennsylvanian-age units are the most abundant strata in the ERMN parks, and this time period is represented in six of the nine network parks, including ALPO, FONE, FRHI, GARI, JOFL, and NERI.
No Precambrian units are mapped within the ERMN parks.
Visit—Park Geology
Type Sections—Eastern Rivers and Mountains Network

The geologic history above is excerpted from a report titled, "National Park Service geologic type section inventory: Eastern Rivers and Mountains Inventory & Monitoring Network". Type sections are essential reference locations for the geoscientists who study geologic history and paleontology. A summary of the type sections in each park can be found at the links below.
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Allegheny Portage Railroad National Historic Site, Pennsylvania (no designated stratotypes identified)
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Bluestone National Scenic River, West Virginia (no designated stratotypes identified)
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Delaware Water Gap National Recreation Area, New Jersey and Pennsylvaniaa (contains 11 identified stratotypes)
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Fort Necessity National Battlefield, Pennsylvania (no designated stratotypes identified)
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Friendship Hill National Historic Site, Pennsylvania (no designated stratotypes identified)
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Gauley River National Recreation Area, West Virginia (no designated stratotypes identified)
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Johnstown Flood National Memorial, Pennsylvania (no designated stratotypes identified)
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New River Gorge National River, West Virginia (contains three identified stratotypes)
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Upper Delaware National Scenic and Recreation River, New York and Pennsylvania (contains four identified stratotypes)
The full Network report is available in digital format from:
Please cite this publication as:
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Henderson T, Santucci VL, Connors T, Tweet JS. 2021. National Park Service geologic type section inventory: Eastern Rivers and Mountains Inventory & Monitoring Network. Natural Resource Report. NPS/ERMN/NRR—2021/2248. National Park Service. Fort Collins, Colorado.
NPS Stratotype Inventory
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Last updated: February 5, 2025