Pennsylvania Geography: Appalachians, Rivers, and Two Great Cities

Pennsylvania's geography is dominated by the Appalachian Mountains — multiple parallel ridges running northeast to southwest across the state, separating the coastal plain and piedmont from the Ohio River drainage.

Ridge and Valley Province
The central and eastern portions of Pennsylvania are a series of long, parallel Appalachian ridges and valleys — Blue Mountain (the easternmost and most continuous ridge), Tuscarora Mountain, Jacks Mountain, Bald Eagle Mountain, and the Allegheny Front (the western escarpment of the Appalachian Plateau). The valleys between the ridges — the Great Appalachian Valley (including the Cumberland Valley and the Lebanon Valley), Nittany Valley, and the Kishacoquillas Valley — are agricultural heartlands.

Allegheny Plateau (Western Pennsylvania)
West of the Allegheny Front — the plateau is a heavily dissected upland of forested hills and deeply carved river valleys. Pittsburgh sits at the confluence of the Allegheny and Monongahela Rivers forming the Ohio — a location that determined the city's role as the gateway to western expansion and the center of US steel production.

Delaware River (Eastern Border)
The Delaware forms the entire eastern border with New Jersey — from Port Jervis in the north to Wilmington, Delaware in the south. The Delaware Water Gap (where the river cuts through Blue Mountain) is a glacially modified water gap of striking beauty. The Delaware River Basin provides drinking water to 15 million people.

Susquehanna River
Pennsylvania's dominant interior river — the Susquehanna and its West Branch drain most of central Pennsylvania before entering Maryland's Chesapeake Bay watershed. The North Branch Susquehanna (from Cooperstown, NY) and the West Branch join at Sunbury. The river is broad and shallow; it is the largest tributary of the Chesapeake Bay.

Pocono Mountains
The northeastern plateau — the Poconos are not high mountains (maximum 2,300 feet) but a broad forested upland plateau, popular for resort and second-home development from the Philadelphia and New York metros. Delaware Water Gap, Bushkill Falls, and Hawk Mountain Sanctuary are in this region.