The Ecology of Hydric Hammocks - USGS National Wetlands ...

far more frequently and extensivelyacross the Florida 1 andscape.2.2 PHYSIOGRAPHY AND GEOLOGYFlorida appears flat and featurelesscompared with the dramatic 1 andformsof the western United States. Allsites are close to the sea horizontallyand vertically: no place ismore than 120 km from the At1 anticOcean or the Gulf of Mexico, andFlorida's highest point is only 105 mabove sea level. Much of the state iselevated 15 m or less (Figure 1). Minorchanges in topography--di fferenceson the order of centimeters ratherthan meters--greatly affect the nature,extent, and distribution ofFlorida's plant communities.Florida lies within the Gulf and Atlanticcoastal-plain province and containsfive major physiographic regions(Figure 3). Finer geomorphic divisionsare described by Puri and Vernon(1964) and White (1970). Maximum localre1 ief occurs within the westernMARIANNALOWLANDSFigure 3. Physiographic regions of Florida. TheFloridan Plateau includes Florida and its submergedcontinental shelves. The edge of theplateau is indicated by the go m depth contour(from Cooke 1939).highl ands of the panhandle, whererolling uplands are cut by narrow,steep-wai i eu biftjd~u vdi 7 ey~, and 1 snext greatest in the central highl andsthat run north and south through muchof the peninsula. Fringing the entirepeninsula and extending to the extremewest of the panhandle, the coastallow1 ands have 1 i ttl e re1 i ef and generallyrise slowly via step-like terracesto the central ridges. The landsurfaces of the Okeechobee plain ofsouthern Florida and the Big Bend area(northeastern corner of .ehe Gulf ofMexico) are virtually flat.Florida's topography and physiographicdivisions have resulted fromthe interplay of sediment deposition(mainly marine), erosion, and solution.Since at least the early Cretaceousperiod, the Florida peninsulahas existed as part of the muchbroader Floridan Pl ateau, a stablecarbonate platform (Puri and Vernon1964). The relative amounts of landand water on the plateau have variedwith fluctuating sea level; at present,the emergent peninsula and thesubmerged continental she1 f that ringsthe state are roughly equal in area(Figure 3). The Floridan Plateau wasformed in warm shallow seas by the depositionof thousands of feet of Cretaceousand Tertiary limestone anddo1 omi te (Figure 4). Some evapori tes(e.g., anhydri te) a1 so were deposited,but only small amounts of clastic(sand, silts, clay) sediments accumulated.The deposits amassed atop thecoastal-plain foundation of sedimentaryand igneous rocks and theirthickness and slope were influenced bythe Peninsular Arch (Figure 4). Extendingdown the peninsula from southernGeorgia to the southeast, the Archis Florida's dominant subsurfacestructure. This deformation probablyresulted from crustal stresses thatwarped the coastal -plain floor duringthe 1 ate Paleocene or early Mesozoic(Applin 1951). In comparison, theoverlying carbonate deposits have experienced1 ittle deformation. Outcroppings of Eocene and 01 igocene1 imestones indicate the Ocal a Up1 i ftin west-central Florida (Figures 4 ands