The Piedmont Plateau: The Gently Rolling Hills of Philadelphia

Hawk Mountain - overlooking the mountains on the Piedmont Plateau
Hawk Mountain – overlooking the mountains on the Piedmont Plateau

The Piedmont Plateau is a vast , naturally forested plain of gently rolling land and small hills, crossed by small streams, creeks and large rivers.

The geologic term for the plateau is peneplain, which means a plain not yet worn entirely smooth by erosion. Small isolated hills , called monadocks, jut upwards from the land.

Atlantic Coastal Plain map
The Atlantic Coastal Plain. Kelvinsong, CC BY-SA 3.0 <;, via Wikimedia Commons

The Piedmont stretches southward from the Palisades along the Hudson River for 1000 miles to the Black Belt of Central Alabama. The Piedmont spreads westward and ends at the Blue Ridge Mountains.

Piedmont Plateau Soils and Minerals

The Piedmont Plateau has reddish clayey soils covering small rolling mounds and hills. The hills are composed of red shale, sandstone, limestone, dolomite, schist and quartzite with some areas of diabase (a very hard igneous rock).

coastal plain meets piedmont
The Atlantic Coastal Plain meets the Piedmont at Bartram’s Garden in Philadelphia.


Piedmont Plateau Meets the Atlantic Coastal Plain

The Piedmont butts up against the Atlantic Coastal Plain. It is often difficult to separate the Atlantic Coastal Plain from the Piedmont. One place I have seen the clear demarcation is along the shoreline in Philadelphia’s Bartram’s Garden. At this place in Bartram’s Garden you can clearly see where the flat Atlantic Coastal Plain butts up against the higher Piedmont Plateau.

Most often the two provinces extend fingers into the other region. Feeling the soil is often a good way. The Atlantic Coastal Plain is sandy and the Piedmont clayey. This only works where the soil hasn’t been amended two much.

High Points

The elevation of the Piedmont Province ranges from 100 to 500 feet. In Philadelphia, the Piedmont Plateau reaches its highest peak of 440 feet at Wissahickon Environmental Center (the “Tree House”) the in Wissahickon Park. This is the highest point in Philadelphia.

That concludes the three-part series on Philadelphia landforms (eco-regions). We started with the idea of bounded space. Next I discussed the two eco-regions of Philadelphia which are: the Atlantic Coastal Plain and the Piedmont Plateau.

Know Your Eco-Region

Knowing the eco-region or the topography of the land and space you live is helpful in learning to live in harmony with the land. It helps to know if your area is prone to flooding if you are buying a house or apartment. Would you rather know a house has an underground basement in a flood zone, before or after you sign the papers?

Landforms of Pennsylvania from PA Dept. of Conservation of Natural Resources.
Landforms of Pennsylvania from PA Dept. of Conservation of Natural Resources.

If you don’t know your eco-regions you can find it here.

Related Posts

Philadelphia Nature: An Overview

Philadelphia’s Coastal Plain

National Wildlife Refuges in the Mid-Atlantic Region

Natural Places in Philadelphia and the Delaware Valley


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