13 barrier islands were formed 30,000 to 40,000 years ago when wind,
wave action and long-shore currents moved sand and other sediments
to form a dune or beach ridge near the ocean shore. Rising sea level
eventually flooded the area behind the dune, creating the band of
marshes and tidal creeks that are present today between the barrier
islands and the mainland.
same process occurred several times along the Georgia coast as sea
level rose and fell during Ice Ages and interglacial periods. The
Altamaha crosses six ancient shorelines as it flows to the sea (Hoyt
and Hails, 1967).