On a map of the continental United States Florida is easily recognized as the southward jutting peninsula separating the Atlantic Ocean from the Gulf of Mexico. Florida is the exposed portion of the Floridan Plateau, a mass of rock nearly 500 miles long and from 250 to 400 miles wide. On top of a foundation of mostly igneous rock, assumed to be a continuation of the geologic base of the Piedmont region of Georgia, are more than 4,000 feet of highly porous sedimentary rock, chiefly limestone, formed over millennia by deposition of shells and bones of sea creatures as well as chemicals evaporated from the shallow seawater.
Over the millions of years of the Florida peninsula's geologic history, its size and shape have changed many times: 50 million years ago it was an island south of North America, 10 million years ago it was completely submerged, and since then peninsulas and islands of various sizes and shapes have been created and redrawn by fluctuating sea levels. Florida's abundance of ridges, sinkholes, springs, rivers, lakes, and plains is the result of these rises and falls of the sea and of the uplift and subsidence of land. The sea is also largely responsible for the state's many bays, inlets, wetlands, and islands. The Florida Keys, a gentle arc of islands extending 150 miles south of the peninsula to Key West, are composed of coral rock covered in most places with a thin layer of sand.
Florida's location between latitudes 24 degrees 30' N and 31 degrees N, the warming influence of the Gulf Stream, and its geologic history result in a climate and an array of plants and animals unlike any other state. The climate of Florida is basically humid subtropical with the exception of the southern tip of the peninsula and the Keys, which are tropical. Long, hot summers are separated from short, cool, and sometimes cold, winters by mild and pleasant days during spring and fall. The Gulf Stream moderates Florida's temperatures year-round. Sea breezes keep land along the coast slightly warmer in the winter and cooler in the summer than inland areas. Climatic differences are smallest in the summer when the state is almost continually under the influence of warm, moist air from the Gulf of Mexico and the Atlantic. During July, the warmest month, temperature differences are small throughout Florida: mean daily maximum values range from 88 to 91 degrees Farenheit, and mean minimum values range from 72 to 75 degrees Farenheit. In the winter temperature differences are far greater across the state: mean daily maximum temperatures during January, the coldest month, range from 75 degrees Farenheit in southern Florida to 60 degrees Farenheit in the western panhandle, and mean daily minimum temperatures range from 60 degrees Farenheit in the south to 40 degrees Farenheit in the north.
With the exception of the north, where rain accompanies winter cold fronts, most of Florida receives the majority of its rain from summer showers and storms, a predictable and welcome afternoon relief from the heat and humidity. The Florida peninsula has been dubbed the "thunderstorm capital" of the northern hemisphere. Only in the heart of sub-Saharan Africa are thunderstorms more frequent than over the Florida peninsula.
Florida averages 54 inches of rainfall annually, more than any other state. Despite its high rainfall Florida has relatively few days when the sun fails to shine at least part of the day. So rare are these days that a St. Petersburg newspaper used to give away its evening edition on sunless days.
Great amounts of rain may fall within short periods of time: 38.7 inches in 24 hours in Yankeetown in 1950, 6 inches in 1 hour in Hialeah (near Miami) in 1947. The heaviest rainfall occurs in a strip 10 to 15 miles inland from the southeast coast and in the western panhandle, which averages 66 inches of rain each year. The Keys normally receive the smallest amount of rainfall-an average of 40 inches each year. Miami Beach averages 47 inches each year, and Miami, only 9 miles inland averages 58 inches. Rain may appear suddenly from a cloudless sky and may fall in one block and not another.
Although rainfall is abundant in Florida, it varies seasonally and annually as well as spatially, sometimes resulting in severe supply problems, particularly in south Florida. Geologist Garald Parker identified a line snaking across the peninsula from New Smyrna Beach to Cedar Key as the Florida Hydrologic Divide. The area south of this line, which supports over three-quarters of the state's population, is totally dependent on rainfall it receives for its water: virtually no net movement of either surface water or groundwater occurs across this line.
All of Florida is susceptible to hurricanes-tropical storms with wind in excess of 74 miles per hour-from June through November, with the greatest number occurring in September and October. Dade County and the Keys have the highest probability of experiencing a hurricane: 1 in 7 in any given year. Thousands of lives, however, were lost to hurricanes earlier in the century. Over 120 people were killed and 5,000 homes destroyed when a hurricane hit Miami in 1926. Two years later over 2,000 people-mostly migrant farm workers-drowned when a dike around Lake Okeechobee broke during a hurricane, an event vividly recounted in frightening detail by Zora Neale Hurston in her novel, Their Eyes Were Watching God. The Labor Day hurricane of 1935 killed over 400 in the Keys. Many were unemployed World War I veterans sent to work on public road projects. They were killed when the train sent from Miami to evacuate them was swept off the track by wind and water.
Even today after decades of intense development and thousands of years of human occupancy, Florida is still a biological wonderland and global hotspot of biodiversity, with a mixture of species derived from more temperate areas to the north and tropical Caribbean areas to the south. Travelling across north Florida and along the St. Johns River in 1777, naturalist William Bartram described large-mouth bass weighing 25 to 30 pounds, diamondback rattlesnakes 10 to 12 feet long, and live oaks with circumferences of 12 to 18 feet. He also identified 400 species of plants, 125 of which were previously unknown to him.
Contemporary biologists estimate that there are 300 species of native trees and 3,500 species of vascular plants in Florida. Today the predominant vegetative community throughout Florida is pine forests. One to three species of pine (longleaf, slash, pond) are found mixed with oak. Herbs, saw palmetto, shrubs, and small hardwood trees form an understory. A century ago, before large-scale drainage and development, as much as 60 percent of Florida's surface was wetlands. Now they occupy 15 to 20 percent. Today mangroves, swamps, and saltwater marshes are still found on the southern rim of the peninsula. Freshwater marshes abound in the Everglades, called Pa-hay-okee-the "grassy water"-by the Indians and "River of Grass" by famous Florida author and environmentalist Marjory Stoneman Douglas. North and west of Lake Okeechobee are wet grasslands. In central Florida, pine flatwoods are interspersed with mixed forests of pine, xerophytic oak, and hardwoods. In the northern panhandle are forests of mixed hardwoods and pines. Where trees have been cut for lumber or pulp, secondary growth consists mostly of pines. Throughout the state, river valleys and large lakes are bounded by cypress forests. Most of the coastline is sandy beaches, saltwater marshes, or mangrove swamps.
Much of the vegetation in the panhandle and the northern part of the state is shared with the rest of the Gulf and the Atlantic coastal plains. Specialized assemblages of plants developed in the central portion of the state when the area was isolated by higher seas. Tropical and subtropical plants, many of Caribbean and South American origin, thrive in the hammocks of south Florida. Florida has over 150 native species of reptiles and amphibians, including the now-abundant alligator and the much rarer American crocodile, as well as over 200 native species of freshwater fi
