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.
Tidal marsh has a heavy vegetative cover of salt-tolerant grasses and reeds.
Tidal marsh islands west of Captree State Park are part of this association. Beaches are subject to continual wave action. Bridgehampton-Haven Association Deep, nearly level to gently sloping, well drained to moderately well drained, medium textured soils on outwash plains. This association is on the south fork of the island, and it extend eastward from Southhampton to Amagansett. The association is on outwash plains.