Geography of the Florida Keys

Historic Bahia Honda Bridge, Florida Keys
Historic Bahia Honda Bridge
Florida Keys

The Florida Keys are an archipelago of about 1700 islands in the farthest southeast portion of the United States. They extend from the southeastern Florida peninsula about 15 miles south of Miami, and run south-southwest gradually curving west to Key West and out to the uninhabited Dry Tortugas. There are over 800 charted islands with about 30 of them inhabited. The Keys lie along the Florida Straits, dividing the Atlantic Ocean to the east from the Gulf of Mexico to the west. The southern tip of Key West is located just 90 miles or 145 km from Cuba.

The Florida Keys are actually made up of exposed portions of an ancient coral reef, with very little sand. Elliott Key, which is the northernmost of the true Florida Keys, is in Biscayne National Park. To the north of Elliott Key are several small "transitional" keys, composed of sand built up around small areas of exposed ancient reef. Barrier islands located further north, are built up of sand and include Key Biscayne and other islands.

Starting approximately 130,000 years ago, the sea levels raised to around 25 feet or 7.5 m. above today's current level. At this time, all of the southern portion of Florida was covered by a shallow sea. A reef consisting of several parallel lines formed along the edge of the submerged Florida plateau and stretched from the Miami area to what is now the Dry Tortugas. This reef formed the Key Largo limestone that you see on the surface of the Keys from Soldier Key to Big Pine Key.

Geography of the Florida Keys
Some of the coastline in the Florida Keys
is fossilized. Make sure you wear footwear!

The Florida Keys are located in the subtropics between 24 and 25 degrees latitude north. The climate and environment are closer to that of the Caribbean than the rest of Florida, though unlike these volcanic islands, plants and animals are what built the Keys.

The Upper Keys islands are remnants of large coral reefs, which became fossilized and exposed as sea level declined. The Lower Keys are composed of sandy-type accumulations of limestone grains produced by plants and marine organisms.

Natural habitats of the Keys are upland forests, inland wetlands and shoreline zones. The soil here ranges from sand to marl to rich, decomposed leaf litter. "Caprock" (the eroded surface of coral formations) covers the ground in some places. Rain falling through leaf debris becomes acidic and dissolves holes in the limestone, where soil accumulates and tree roots find purchase.

The climate is subtropical and because of this, the Keys are the only frost-free place in Florida. There are two main "seasons" - from about June through October it is hot, wet, and humid, and from November through May the Keys will have drier and cooler weather. Many plants grow slowly or go dormant in the dry season. Some native trees are deciduous, and drop their leaves in the winter or spring.

The Keys have distinctive plant and animal species, some found nowhere else in America. The climate also allows many imported plants to thrive here. Almost any houseplant along with most plants that landscape the South, can thrive in the Keys climate. Some exotic species now invade and threaten natural areas of the Keys. Though not native plants to the Keys, you will see an abundance of coconut palm, bougainvillea, hibiscus, and papaya.

Key Deer
Key Deer are found only in the Florida Keys

The well-known Key lime, otherwise known as the Mexican lime, is a naturalized species, which was introduced to the Keys from the Yucatan Peninsula of Mexico. The tree grows rapidly, has thorns, produces golf-ball-size yellow fruit (which are very sour!) and is wonderfully fragrant. Of course, Key lime pie was invented here!

The Keys are home to some our most unique animal species in the United States, including the Key deer, protected by the National Key Deer Refuge, and the American crocodile. Located about 70 miles or 110 km. west of Key West is Dry Tortugas National Park, one of the most isolated and therefore well-preserved parks in the world. From a distance, the Dry Tortugas look like dry tortoise (in Spanish tortoise is tortuga) shells which is of course how their name came about.