Porous Limestone Beneath the Flat Everglades

Within the rock, tiny fragments of shell, sand and bryozoans were pressed together in layers to form small grains called ooids. The spaces between these grains let water move through the stone and hold it, which makes the limestone porous.

The land is flat, with elevation running from sea level up to about 8 feet. A couple of inches of height can change which plants and animals live there. The highest ground supports slash pine forest with saw palmetto beneath it, and fire keeps hardwoods from taking over. A little lower, cypress heads appear, and lower still lies swampland dotted with small hills covered in tropical hardwoods.

Much of the water is held in the porous limestone, and most of it arrives as rain. An underground reservoir called the Floridan aquifer lies about 1,000 feet below South Florida, and no underground springs feed the system. Rain falling to the north feeds the Kissimmee River and Lake Okeechobee, and overflow from the lake spreads into a river 40 to 70 miles wide that barely seems to move.

Water moves across the land through freshwater sloughs, low-lying channels that carry it about 100 feet per day. Parallel ridges of higher ground run alongside them, forming the ridge and slough pattern that shapes much of the landscape. Shark River Slough and Taylor Slough are two significant sloughs in the park. Sawgrass growing 6 feet or more helped earn the Everglades its nickname, the River of Grass.

In the southern and southwestern reaches, tides bring in salt-tolerant plants such as mangroves. On the Gulf Coast, the Calusa people built a shell mound that rises 20 feet above sea level, a notable high point in such flat country.