The Piedmont Plateau: The Gently Rolling Hills of Philadelphia

Looking up a forested hill at the Schuylkill Center in the Piedmont.
Looking up a forested hill at the Schuylkill Center in the Piedmont.

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.

Hawk Mountain (on the Piedmont Plateau)
Hawk Mountain (on the Piedmont Plateau) in the Blue Ridge Mountains

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.

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).

The flat Atlantic Coastal Plain butts up against the Piedmont Plateau at Bartram's Gardens.
The flat Atlantic Coastal Plain butts up against the Piedmont Plateau at Bartram’s Gardens.

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.

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.

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?

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

A hidden pond at Schuylkill Center for Environmental Ed.
A hidden pond at Schuylkill Center for Environmental Ed. in the Piedmont. Yes, this is in the city.

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