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Western Allegheny Plateau

Last updated: July 3rd, 2026

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Name	†	Color on Map	EPA Code‡
Permian Hills	…		70a
Monongahela Transition Zone	…		70b
Pittsburgh Low Plateau	…		70c
Knobs-Lower Scioto Dissected Plateau	○		70d
Unglaciated Upper Muskingum Basin	○		70e
Ohio/Kentucky Carboniferous Plateau	○		70f
Northern Forested Plateau Escarpment	○		70g
Carter Hills	○		70h

† Status: ✓ = Complete ○ = Needs Image … = Incomplete ∅ = Stub Only

‡ This code refers to the US EPA's Level 4 ecoregion codes for the continental U.S., see here.

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↑About the Western Allegheny Plateau

The Western Allegheny Plateau is a broad region extending roughly northeast-southwest from southwest Pennsylvania through much of northwest West Virginia and southeast Ohio, into northeastern Kentucky.

This area lies just to the southeastern border of recent glaciation, so it has not been glaciated, but areas to the northwest have been. The terrain mostly consists of a heavily-dissected plateau with rugged hills. Although the topography is relatively steep when viewed on a small scale, taken on a large scale it is quite flat, lacking the higher elevations and more dramatic peaks of the Appalachian ridges to the southeast. The underlying bedrock is sedimentary, mostly from the Carboniferous period. Bituminous coal is found throughout and its mining played a key role in the recent history of this region. The rock layers are most horizontal here, leading to patchy distribution of different soil types that varies locally by elevation but is relatively homogenous on a large scale.

The climate is humid and continental with warm to hot summers and cold winters. The original forest cover here is mostly mixed mesophytic forest, with some smaller areas of Appalachian oak forests on the warmer, drier sites. Dominant tree species include chestnut oak (Quercus montana), red maple (Acer rubrum), white oak (Quercus alba), black oak (Quercus velutina), American beech (Fagus grandifolia), American tuliptree (Liriodendron tulipifera), sugar maple (Acer saccharum), American basswood (Tilia americana), yellow buckeye (Aesculus flava), and eastern hemlock (Tsuga canadensis). American chestnut (Castanea dentata) was once common here but was mostly eliminated by the Chestnut Blight. white ash (Fraxinus americana) was common here until recently when the Emerald Ash Borer caused widespread diebacks. Beech tends to be less common here than to the northwest, where it is dominant.

Nowadays, this region is mostly forested, with small amounts of agriculture, including livestock and dairy farming, and cultivation of hay, corn, small grains, and tobacco. There is some logging and forestry in the area, as well as some protected national forests. Coal mining is extensive, causing extensive environmental problems including degradation of waterways. Pittsburgh is the largest city in this region, which also contains numerous smaller cities.

This area is bordered to the southeast by the more rugged and higher-elevation Central Appalachians and to the northwest by the glaciated and much flatter Erie Drift Plain. Southwest of that, but also to the northwest, this region also shares a small border with the Eastern Corn Belt Plains, and south of that, to the west by the Interior Plateau. There is also a small border to the southwest with the Southwest Appalachians.

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↑References

1. Wiken, E., Griffith, G. "North American Terrestrial Ecoregions - Level III", Commission for Environmental Cooperation, (2011) Web.