Key Largo - Geology and Geography

Geology and Geography

The island of Key Largo is an exposed, fossilized remnant of a coral reef formed during a period of higher sea level and then uncovered and eroded during a subsequent ice age. The highest elevation is a slight ridge forming the spine of the island, which rises to about 15 feet (4.6 m).

The island's substrate is called Key Largo limestone; in many places, fossilized corals and smooth, eroded limestone "caprock" are visible at the surface. Solution holes, which are pockets dissolved in the limestone by acidic rainwater, form shallow depressions in the land. The natural shoreline of the island is generally rocky. A slippery, gray, limestone-based clay called "marl" is the shoreline and near-shore soil. There are no natural sand beaches on the island. Inland, decomposed vegetation forms a rich, acidic humus soil up to about six inches thick, topped by "leaf litter". The soil supports a diverse flora of herbaceous plants, woody shrubs and hardwood trees.

Key Largo's climate is considered tropical. Frost has never been recorded in the island.