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A Santee River B
floodplain N Detailed N
geologic maps
33°30ʹN 3 3°30ʹN unavailable

3 3°N

3°N
3 32°30ʹN

3A

80°30ʹW 80°W 7 9°30ʹW

C
32°30ʹN 3B 33°30ʹN Detailed N
geologic maps
D-E unavailable

80°30ʹW 8 0°W 79°30ʹW

3 3°N
Mean Th (ppm) Th Skewness

32°30ʹN
D Increasing Age E Increasing Age

80°30ʹW 80°W 7 9°30ʹW
Figure 2. (A) Airborne eTh over the 2019 survey area and approximate heavy mineral percentages (circles) from visual observations of
auger samples (see text footnote 1, item S2); green box shows area used for statistical calculations (D and E); yellow boxes show loca-
tions of close-ups in Figure 3. Gray dashed lines show the location of a buried paleochannel. (B–C) Airborne eTh for sands only (B) and
clays/muds only (C). (D) Mean and (E) skewness values of eTh (parts per million [ppm]) for the various geologic units. H—Holocene;
SB—Silver Bluff Beds; Wd—Wando; TM—Ten Mile Hill; Ld—Ladson; P—Penholoway; W—Waccamaw.

+
33°N M
79°45’W
M
M
M +
32°40’N
80°20W

N
10 km

0 2 4 6 810
RadiometriceTh (ppm) A 10 km N B

Figure 3. Close-ups of eTh draped over a lidar elevation shaded relief map (see text footnote 1, item S4) north (A) and south (B) of Charles-
ton. eTh highs are often located along the shoreface and near streams or inlets. Highest values occur near areas marked “M” that expe-
rienced multiple episodes of reworking by marine processes.
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