The topography of the association is typical of sand dunes and beaches. It has uneven dunes slightly inland from the beaches. This association makes up 5 percent of the county. Dune land makes up about 40 percent of the association, tidal marsh makes up about 35 percent, and beaches about 15 percent. Areas where dredgings have been placed on tidal marshes or dunes make up the remaining 10 percent.
Dune land is made up mainly of nearly even-sized sand grains that have been piled up by winds.
Vegetation is sparse on most dunes except in the Sunken Forest and a potion of the area near Napeague. In places dunes have encroached on marshes, and the water table is within 2 or 3 feet of the surface. Tidal marsh had an organic surface layer that ranges from a few inches to several feet in thickness. The organic surface layer is underlain by white sand. The water level is at or near the surface throughout the year, but flood occur only during abnormally high tides.