The geologic structure of Orange Lake in general is a semi-confining unit overlying limestone karst. The Plio-Pleistocene surficial sediments include sands and clays that range in thickness from ~1 m (~3 ft), over most of the area, to about 20 m (67 ft) in the Fairfield Hills. These sediments are underlain by clays, sandy clays and carbonates of the Miocene Hawthorn Group. Natural gamma logs from boreholes adjacent to Orange Lake indicate that the clays range in thickness from about 5 m south and southwest of the lake, to more than 25 m (82 ft) on the east side. Horizon HL in profile A-A’ below may represent the top of the Hawthorn Group. The Ocala Limestone carbonates are the oldest units exposed in this area and can be seen in roadcuts and numerous quarries. The contact between units exhibits highly irregular surfaces typical of karst. The top of the Ocala Limestone range from about 6 m to > -6 m (20 to > -20 ft) NGVD, with an overall trend dipping to the northeast. Dissolution of the carbonate is active and can be seen at the Heagy-Burry Park. For years, dirt fill has been periodically brought to an actively subsiding sinkhole on the east side of the park’s boat ramp and is representative of cover subsidence sinks in Orange Lake. Land-based ground penetrating radar profiles from the park adjacent to the collapse sinkhole indicate numerous buried sinkholes and cavities (Davis, 1996).

Additional work regarding Orange Lake not included in this summary can be found in Kindinger and others (1994, 1998).