Whitewater Falls, NC/SC
tallest and among the longest waterfall in Eastern US - right on the border between NC and SC.
Info from web:
Upper Whitewater Falls is the highest waterfall east of the Rockies. The falls plunge an amazing 411 feet! South Carolina's Lower Whitewater Falls drops another 400 feet. Because of the escarpment's difficult access and rugged terrain, much of the area receives few visitors and has remained wild and undeveloped over the years.