FLORIDA GEOLOGICAL SURVEY


inversion, is thought to have been an important
factor in the origin of the Brooksville Ridge
(White, 1970; Knapp, 1977). Karst features are
abundant along the axis of the Brooksville
Ridge. These features are generally internally
drained and locally breach the low-permeability
sediments in the subsurface and serve as focal
points of aquifer recharge. Ecosystems present
within the Brooksville Ridge area include scrub
and high pine, temperate hardwood forests (with
less extensive swamps), pine flatwoods, and dry
prairies (Crumpacker, 1992).

 The Western Valley is located east of the
Brooksville Ridge and Tsala Apopka Plain and
west of the Sumter and Lake Uplands (Figure 6).
It is also bound to the north by the Northern
Highlands and the Polk Upland to the south. The
Western Valley is approximately 140 mi (225
km) long and between 5 and 15 mi (8.0 to 24.1
km) wide; elevations average approximately 40
ft (12.2 m) MSL and range up to 100 ft (30.5 m)
MSL. Ecosystems present in the Western
Valley include temperate hardwood forest (to
the north), scrub and high pine, minor swamps,
pine flatwoods and dry prairies (Crumpacker,
1992). The Western Valley is characterized by
its gently rolling limestone karst plains
containing a veneer of Pleistocene sediments
overlying Eocene carbonates (Rupert and
Arthur, 1990). The Tsala Apopka Plain is
believed to be a relict feature of a larger paleo-
lake (White, 1970). Scott (2004) proposes
reclassification of the Western Valley into the
Williston Karst Plain and Green Swamp Karst
Plain.

 The Polk and Lake Uplands, located between
the Gulf Coastal Lowlands and the Lake Wales
Ridge are approximately 100 mi (161 km) in
length and range in elevation from 80 ft (24.4 m)
MSL to 130 ft (39.6 m) MSL. Pine flatwoods
and dry prairies with lesser amounts of
temperate hardwood forest, scrub and high pine
comprise the ecosystems in these uplands
(Crumpacker, 1992). A scarp with relief of
approximately 25 ft (7.6 m) separates the Polk
and Lake Uplands from the Gulf Coastal
Lowlands and Western Valley (Arthur and
Rupert, 1989). These two uplands contain three
minor ridges: the Winter Haven Ridge, the Lake
Henry Ridge and the Lakeland Ridge (White,


1970). The land surface is comprised mostly of
mild to gently rolling hills gradually increasing
in elevation eastward. Miocene-Pliocene clays in
this region overlying older carbonates create a
hydrogeologic environment conducive to the
rapid formation of large cover-collapse
sinkholes. Scott (2004) proposes to rename the
Polk Uplands in combination with the DeSoto
Plain: the Polk-DeSoto Plain. The part of the
Lake Upland in the present study area is
proposed to be renamed the Green Swamp Karst
Plain (Scott, 2004).

 The DeSoto Plain is a broad, gently sloping
area south of the Polk Upland, east of the Gulf
Coastal Lowlands and west of the Lake Wales
Ridge. Elevations vary between 30 and 100 ft
(9.1 to 30.5 m) MSL (Wilson, 1977). The
DeSoto Plain varies from 10 to 40 mi (16.1 to
64.4 km) in length from north to south and 10 to
50 mi (16.1 to 80.5 km) in width from west to
east. Ecosystems present within the area include
pine flatwoods and dry prairie with minor
swamp, scrub and high pine (Crumpacker,
1992). The lithology consists of thick sandy
clays over Pliocene and Miocene limestones of
poor induration.

 The most prominent geomorphic feature in
the study area is the Lake Wales Ridge. This
large elongate upland extends from Lake County
south to Highlands County, where it is flanked
by paleodune fields on the eastern margin (Scott
et al., 2001). Ecosystems on the Ridge include
freshwater marsh, pine flatwoods and dry
prairies (Crumpacker, 1992). A belt of lakes
dominate the Intraridge Valley in the southern
part of the Lake Wales Ridge. Geophysical
investigations of lakes within the Intraridge
Valley confirm a karst-related origin: irregular,
discontinuous seismic reflectors underneath
some lakes reveal breaches through confining
beds overlying the FAS (Evans et al., 1994;
Tihansky et al., 1996), thus indicating that the
large collapse features occurred prior to or
during Pliocene siliciclastic deposition (Arthur
et al., 1995).

 Elevations on the Lake Wales Ridge range
from approximately 70 to 312 ft (21 to 95.1 m)
MSL, the latter forming a hilltop feature known
as Sugarloaf Mountain in Lake County. Unlike
the geology of the Brooksville Ridge, the Lake