A Quick View of the Florida Keys
The word “key” as it relates geographically to south Florida originated from the Spanish word cayo for “little island” or “island reef.” All small marine islands in south Florida are called keys. The group of islands that comprise the archipelago that stretches about 125 miles from Key Largo to Key West is known collectively as the Florida Keys. Most are linked by roads and 42 bridges, but there are undeveloped and unconnected islands on both ends.
The Florida Keys are composed of several forms of limestone. Exposed very recently geologically, these 5,000-year-old islands are barely separate from the sea. They rise an average of 2 to 4 feet above sea level, with the highest islands (Key Largo, Plantation, Windley, Lignumvitae, and Big Pine) rising only to 18 feet. Actually, the landfills create the highest land now in the Keys.
From Soldier Key in the north to part of Big Pine Key in the south, the substrate rock is Key Largo limestone, an old coral reef. Fossilized remnants of coral skeletons can be easily seen on surface rocks in many places on the Upper Keys. Look for a place, even a parking lot on US 1 in Key Largo, that has rocks on the ground and you will probably see striations from former coral colonies. The more serious geology students will want to visit Windley Key Quarry (see entry for Windley Key Fossil Reef Geological State Park) to get the real picture.