The area of Sand Key at the Indian Rocks location is the narrowest portion of the barrier-island system in the entire study area. The back-barrier environment is only about 200 m wide and the barrier itself is about 100 m wide. The Indian Rocks headland is dominated by the presence of Miocene limestone at sea level along the landward shoreline. The bedrock surface dips steeply in the gulfward direction as shown by the stratigraphic section along the transect (Yale, 1997). The organic muddy sand of the vegetated paralic environment is absent over most of the transect, probably as the result of relatively high-energy wave climate in the headland area which removed it. The barrier displays a typical wave-dominated character with apparent back-barrier muddy shelly sand beneath the facies of the barrier island itself. The barrier consists of beach, dune, and supratidal washover deposits. Although the age of formation of Sand Key is unknown, a piece of detrital wood taken from 1.5 m below the surface of the island was dated at 1,150 (YBP).