OPEN-FILE REPORT 92


 Methods

 The study consisted of 1) reviewing and compiling existing geologic literature and data,
2) mapping geologic units in the field at 1:24,000 scale using standard techniques, 3) core and
cuttings analyses of existing samples, 4) new core drilling, 5) collecting and describing outcrop
samples, and 6) preparing a geologic map, geological cross-sections, and geomorphic map of the
area. Field work, performed during the fall of 2007 and the spring and summer of 2008,
consisted of sampling and describing numerous outcrops, river and pit exposures. One hundred
and twenty-four new samples of geologic material were added to the FGS surface-sample
archives (M-Series), six new cores were drilled, and over 200 outcrops were examined during
this project. All data, including data from over 350 wells, were compiled and analyzed by the
authors. The map and accompanying plates were developed in ESRI's ArcGIS ArcMap 9.2 for
publication as part of the Florida Geological Survey Open-File Map Series.
 The study area is blanketed by a veneer of Quaternary sediments and soils. For this
reason, and in keeping with geologic mapping practices developed by Scott et al. (2001), the
authors have adopted the policy of mapping the first named geologic unit within 20 feet (6.1
meters) of the surface. If undifferentiated Quaternary (Qu) sediments attain a thickness greater
than 20 feet (6.1 meters), then they appear as the mapped unit. If these undifferentiated
sediments are less than 20 feet (6.1 meters) thick, then the underlying stratigraphic unit appears
on the map.
 The region is generally vegetated, and public access in the northern portion of the
mapped area is hindered by the presence of numerous farms and privately owned land. Much of
the southern portion of the study area is owned by a large timber company (Foley Land and
Timber Company) and permission was obtained to access the area for field work and drilling
operations. Fieldwork access was typically limited to public roads, State-owned lands, Foley
property, and Suwannee River Water Management District-owned lands. Access to a large tract
of land (the Avalon Plantation) located in the west-central portion of the study area was not
granted by the owners of the property (Figure 1 on OFMS 99-01). Therefore, new field data in
this region was limited to public-access roads.

 Previous Work

 The current study builds on many previous geologic investigations in and around the
present map area. The Florida Geological Survey has previously published reports on the
geology of Jefferson (Yon, 1966), Taylor (Rupert, 1996) and Madison (Hoenstine et al., 1990)
Counties that were very useful in preparing this report. A statewide geologic map (Scott et al.,
2001) was published by the FGS in digital format and provided much of the base map material.
Preliminary county geologic maps have been published for Madison (Campbell, 1993a),
Jefferson (Rupert and Yon, 1993), and Taylor (Campbell, 1993b) Counties at scales of
1:126,720. It is important to point out, however, that each of these Open-File Map Series
geologic maps were constructed in an average time-frame of two weeks utilizing selected in-
house geologic data with little to no extra field work. Although these maps provided an excellent
starting point for the detailed geologic mapping undertaken for this project, significant
refinement of the geologic maps was possible as a result of this project. This study also benefited
from the work performed for geologic mapping in the eastern portion of the USGS Perry 30 x 60
minute quadrangle (Green et al., 2007). Many of the field relationships and stratigraphic