The area dates back to the Tertiary Age. Topographic features of the area are a result of erosion of sediments that have exposed limestone, carbonate marine sediments. The county is a karst area with limestone at or near the soil surface. In areas where limestone is not at the soil surface, a thin layer of sandy soil is above the limestone. The region is one of two locations where Ocala limestone is exposed and the only location with Marianna limestone at the surface.
Limestone is porous and allows rapid movement of water and chemicals to groundwater supplies.
Sinkholes, subsurface streams, and caverns are also common in the area. More than 4000 sinkholes are located in a 320-square mile area. Solution sinkholes are the dominant sinkhole with a thin layer of permeable sand above limestone or an exposed limestone surface. The sinkholes develop due to a gradual downward movement of the land surface. The karst terrain allows water to dissolve limestone below the surface.