"Roughly 100 miles inland from Virginia’s coast, a geologic boundary called the fall line marks a change in the landscape. Here the sandy soil of Virginia’s coastal plain segues into the bedrock underlying the Piedmont. The effect is pronounced on rivers, where waterfalls and rapids form. Historically, these acted as barriers to ocean-faring vessels.
Towns formed up and down the fall line to handle commerce between inland farmers and coastal traders. Prince William Forest Park, a small national park straddling the fall line in Prince William County, is tied to this history through the tobacco farmers and miners who used the nearby port town of Dumfries to ship their goods. Today the park still receives heavy use, but now hikers, cyclists, and nature lovers are drawn by the cascades, wildlife, rare plants, and historic ruins."