Geological History of Dry Tortugas National Park
The Dry Tortugas are an atoll-like, elliptical coral reef formation which is round about 27 km long, and 12 km in width. The waters between the reefs are pretty shallow, only between 12 and 20 meters. This cluster of seven small islands has been a National Park since 1992.
Geologically speaking, you may be forgiven for thinking that the atoll-like reef is volcanic, but it isn’t. The primary bedrocks which underline the Dry Tortugas are the same as those from much of the rest of southeastern Florida, from the Pleistocene age. There’s plenty of Key Largo Limestone and Miami Limestone around. Some of the islands which make up the Dry Tortuga National Park are actually made up of large piles of unconsolidated carbonate sands, Holocene sands, corals, algae and debris.