The peninsula of Florida is the exposed, "high ground" of the Florida Platform, a broad, southward extension of the North American Plate. Stretching from southern Georgia to the Florida Strait, the Platform's east edge is just a few miles offshore at Miami and about 30 miles off the Atlantic Coast at Jacksonville; on the other hand, the west edge is 100 miles west of the peninsula's Gulf Coast.
The deep, basement rocks of the Florida Platform were originally part of northwest Africa when the Continents merged into Pangea, 250 million years ago. Then, as Pangea broke apart and the Atlantic Ocean opened, this piece of crust broke from Africa and drifted westward with the North American Plate. Initially covered by the sea, parts of the Platform began to emerge late in the Mesozoic Era as sediments accumulated on its surface and sea levels waxed and waned. Fluctuating sea levels continued through the Tertiary Period and much of the limestone in northern and central Florida was deposited during that time (especially from the Eocene through the Miocene).
Dramatic changes in sea level occurred during the Pleistocene Epoch as Continental Glaciers advanced and retreated. It was during this time that the limestone of southernmost Florida and the Florida Keys was deposited; the springs and caverns of north-central Florida also formed during the Pleistocene and high, interglacial seas left remnant dunes across the peninsula. Finally, during the Holocene, which continues today, current vegetation patterns developed and the Everglades formed; south of the Keys, on the southernmost part of the Platform, living coral reefs dot the shallows, destined to become islands of future Florida.