Atlantic Plain

The Atlantic Plain is one of eight distinct physiographic divisions of the contiguous United States. Using the USGS physiographic classification system, the Atlantic Plain division comprises two provinces and six sections. The Coastal Plain province is differentiated from the Continental Shelf province simply based on the portion of the land mass above and below sea level.^[1]

The lands adjacent to the Atlantic coastline are made up of sandy beaches, marshlands, bays, and barrier islands. It is the flattest of the U.S. physiographic divisions and stretches over 2,200 miles (3,500 km) in length from Cape Cod to the Mexican border and southward an additional 1,000 miles (1,600 km) to the Yucatán Peninsula. The central and southern Atlantic Coast is characterized by barrier and drowned valley coasts. The coastal Atlantic plain features nearly continuous barriers interrupted by inlets, large embayments with drowned river valleys, and extensive wetlands and marshes.^[2] The Atlantic plain slopes gently seaward from the inland highlands in a series of terraces. This gentle slope continues far into the Atlantic and Gulf of Mexico, forming the continental shelf. The relief at the land-sea interface is so low that the boundary between them is often blurry and indistinct, especially along stretches of the Louisiana bayous and the Florida Everglades.