Coastal Classification Atlas

Geologic Setting

The eastern panhandle coast of Florida between Lighthouse Point and St. Andrew Bay Entrance Channel consists of sandy beaches and barrier islands. A prominent physiographic feature is the Apalachicola River and Delta complex where both the Gulf and mainland shorelines change orientation. The Gulf shoreline changes orientation around this promontory because the headland is composed of Pleistocene sand deposits, which have acted as a source of sediment for the barrier islands. Barrier islands with numerous beach ridges, such as Dog Island and St. Vincent Island, record abundant sand supply and advancement of the Gulf shoreline when they formed several thousand years ago. Barrier islands also characterize the coast north of the promontory. An exception is the mainland shore along Mexico Beach where a barrier is absent and a low erosional scarp is a prominent topographic feature landward of the beach and dunes. The beach sand typically contains some broken shell material as a result of high production of mollusks in the clear warm water of the Gulf of Mexico and an absence of rivers that would supply additional sand.