The Waccasassa Flats in the central part of Gilchrist County, Florida, comprise an area of about 125 square miles.
The present land features of the Flats are a result of marine processes that occurred during the Pleistocene. The Flats are not actually flat, but instead consist of sand hills that represent a relict barrier island. The barrier island lies closely parallel with the westward facing escarpment of the Brooksville Ridge along the eastern edge of the Flats. The area is underlain by Miocene and Pleistocene clastics that retard the percolation of water. This results in a perched water table and contributes to the swampy conditions which stand out so prominently on the aerial photographs.
Part of the Waccasassa Flats is underlain by the Bronson graben, developed during the movement of the Tertiary rocks that formed the Ocala uplift at the end of Oligocene time.
Rocks studied in the area range in age from late Eocene to Pleistocene and include the upper Eocene, Williston and Crystal River Formations, the Miocene Alachua Formation, and Pleistocene sands.