The Piedmont is the province farthest east of the Appalachian Mountains, stretching 1,000 miles between southern New York and Alabama. A transitional upland bridging higher country to the west and the low woods and swamps of the Atlantic-Gulf Coastal Plain eastward, the Piedmont is generally a low, rolling plateau strung with shallow valleys. Several landforms are particularly notable in the region.
West of the Piedmont is more rugged terrain of the Appalachians. At its southern toe in Alabama and Georgia and in its northwestern extent in Pennsylvania it borders the Valley and Ridge province. In between those abutments, the Blue Ridge lines the western Piedmont from northern Georgia to southern Pennsylvania. Some of the Appalachian Mountains’ most imposing, high-relief ranges lie in the Blue Ridge province, including the Great Smoky Mountains along the Tennessee-North Carolina line and the Black Mountains of North Carolina, which include the chain’s highest summit, 6,684-foot Mount Mitchell. The Piedmont’s northern end abuts the New England province of the Appalachians.
The eastern boundary of the Piedmont constitutes one of the great topographic frontiers in North America, the Fall Line. Here rivers tumble in waterfalls and cataracts off the older and more resilient rocks of the plateau to the low-lying Atlantic-Gulf Coastal Plain. The Fall Line has had major implications for human settlement along the East Coast for centuries: It marked the farthest upstream point for shipping in the big Coastal Plain rivers as well as the farthest downstream for relatively easy crossing of the narrower drainages above the drop.
Isolate lone summits are common in the Piedmont, composed of rock more resistant than surrounding layers that end up being eroded and weathered away, leaving the tougher material as outcrops. In North America, these landforms are often called monadnocks, which stems from an Abenaki Indian word for a New Hampshire peak that may mean “the mountain that stands alone” or “smooth mountain.” Elsewhere they go by the moniker “inselberg.” Notable examples in the Piedmont include Georgia’s Stone Mountain, whose north face bears a large rock carving of Jefferson Davis, General “Stonewall” Jackson and General Robert E. Lee, and Kennesaw Mountain in the same state, where a major Civil War battle was fought in 1864.
Hudson River Palisades
Among the most famous geologic features in the immediate vicinity of New York City, the Palisades are a belt of columnar traprock along the western shore of the Hudson River. They stem from an intrusion of an igneous diabase sill into weaker sedimentary layers of the Newark Basin, one of the structural depressions in the Piedmont, some 200 million years ago. Erosion of surrounding sandstone and shale left the traprock sheet exposed. They exceed 600 feet in elevation and support critical natural communities such as mixed-oak forests and talus aprons.