List of geologic units by type with numeric value corresponding to USGS shadeset (c500)

.390 af - Artificial Fill.  Sand or clayey sand of diverse origin.  
          Used as fill for roads, dams, and other contruction. 
          Ranges from 3 to 10 ft (1-3 m) thick.  Deposits are less than 300 years old.

.225 Qal - Alluvium (Holocene).  Sands presently migrating down drainage courses, 
           frequently veneered by thin mucks and peats at the surface.

.131 Qtf - Tidal Flat (Holocene).  Intertidally exposed mucks, mucky sands, sands.  
           Undifferentiated.

.204 Qht - Tidal-marsh deposits (Holocene).  Clayey sand and clay, medium gray (N5) 
           to black (N1), soft, organic rich. Dominant clay mineral is kaolinite, 
           with significantly less illite/smectite and illite. Deposits 0 to 10 ft (0-3 m) 
           thick and support marsh grass. Known ages less than 5 ka.

.397 Qhs - Beach and barrier-island sands (Holocene).  Quartz sand, very light gray (N8), 
           fine grained, well sorted, shelly; dark, very fine grained heavy minerals 
           abundant. Age less than 10 ka, and surface deposits probably less than 1 ka. 
           Deposits 0 to 35 ft thick.

.220 Qsbc - Silver Bluff beds (informal). Estuarine deposits (Pleistocene, between 33 and 
            85 ka).  Silty to sandy clay, and quartz sand, medium gray (N5) to dark 
            gray (N3), fine grained, clayey. Kaolinite is dominant clay mineral with 
            lesser amounts of illite/smectite and illite. Sediment is dewatered 
            sufficiently to form firm ground.  Deposits 0 to 10 ft (0-3 m) thick.

.246 Qsbs - Beach to barrier-island deposits (Pleistocene, between 33 and 85 ka).  
            Quartz sand, grayish orange (10YR 7/4), fine grained with a minor but 
            persistent coarse-grained fraction, bimodally well sorted; dark, very fine 
            grained heavy minerals abundant; prominently crossbedded. Auger hole CH 7 
            includes typical section. Deposits up to 10 ft (3 m) thick.

.197  Qhm - Freshwater stream and swamp deposits (Holocene to Pleistocene (Wisconsinan) 
            glacial age).  Peat and muck, moderate brown (5YR 3/4) to black (N1), thin, 
            soft, accumulating along imponded stream courses and in ovoid-shaped 
            depressions mostly on Ten Mile Hill and Wando depositional surfaces. 
            Deposits located mainly from aerial photographs and topographic base.  Known 
            ages range from modern to at least 34 ka.

.285 Qwc - Wando Formation (Pleistocene, about 70-130 ka).  Clayey sand and clay facies.  
           Clay, mottled pale grayish orange (10YR 7/4) and medium light gray (N6), silty 
           to sandy; clayey quartz sand, mottled pale grayish orange (10YR 7/4) and 
           medium light gray (N6). Fine to medium grained. Dominant clay mineral is 
           kaolinite with illite and illite/smectite in variable proportions. Soil profile 
           poorly developed compared to Ten Mile Hill beds and older terrace units; 
           grayish-yellow (5Y 8/4) to dark-yellowish-orange (10YR 6/6) B-horizon; 
           base of B-horizon usually 6 ft (1.8m) deep. Unit covered, in places, 
           by modern swamp deposits less than 3ft (1 m) thick. Underlies Princess Anne 
           terrace surface at altitudes below 20 ft (6 m). Wood and terrestrial vertebrate 
           fossils indicate formation in estuarine to fluvial environments. Unit is up to 
           35 ft (11 m) thick.

.23 Qws - Wando Formation (Pleistocene, about 70-130 ka).  Barrier sand facies.  
          Quartz sand, medium gray (N5) to light brown (5YR 6/4) where fresh, may be 
          dark yellowish orange (10YR 6/6) to grayish orange (10YR 7/4) or humic 
          dusky yellowish brown (10YR 2/2) in upper 7 ft (2 m); fine grained; dark, 
          very fine grained heavy minerals abundant.  Dominant clay mineral is 
          vermiculite. Forms Mount Pleasant barrier system mostly at altitudes from 15 to 
          27 ft (4.5-8 m). Unit up to 25 ft (8 m) thick.

.16 Qwf - Wando Formation (Pleistocene, about 70-130 ka).  Fossiliferous shelf-sand 
          facies.  Quartz sand, medium gray  (N5), fine to medium grained, phosphatic, 
          bioturbated.  Clay mineral are kaolinite, illite/smectite, and illite in order 
          of decreasing abundance.  Commonly contains diverse molluscan fauna. Basal 
          contact commonly marked by a layer 1 to 2 in. (3-5 cm) thick of course grained 
          sand, black phosphate pebbles, and worn and  rounded bones and teeth.  
          Auger hole CH 7, includes a typical section.  Unit up to 20 ft (6 m) thick. 
          Shown only in cross section.

.7 Qwls - Wando Formation (Pleistocene, about 70-130 ka).  Barrier sand facies.  
          Quartz sand, medium gray (N5) where fresh, may be dark yellowish orange 
          (10YR 6/6) to grayish orange (10YR 7/4) or humic dusky yellowish brown 
          (10YR 2/2) in upper 7 ft (2 m), fine grained; dark, very fine grained heavy 
          minerals abundant. Dominant clay mineral is vermiculite. Auger hole CH 12 
          includes a typical section. Forms Awendaw barrier system mostly at elevations 
          from 20 to 35 ft (6-11m).  Unit up to 20 ft (6m) thick.

.98 Qwlf - Wando Formation (Pleistocene, about 70-130 ka).  Fossiliferous shelf-sand facies. 
           Quartz sand, medium gray (N5), fine to medium grained, phosphatic, bioturbated.  
           Dominant clay minerals are kaolinite, illite/smectite.Commonly contains diverse 
           molluscan fauna. Basal contact commonly marked by a layer 1 to 2 in. (3-5 cm) 
           thick of course grained sand, black phosphate pebbles, and worn and rounded 
           bones and teeth.  Auger hole CH 12  includes a typical section.  Unit up to 
           15 ft (4.5 m) thick. Shown only in cross section.

.265 Qtmf - Ten Mile Hill beds (informal) (Pleistocene, about 200 to 240 ka).  Fossiliferous 
            sand facies.  Quartz sand, medium gray (N5), fine to medium grained, silty, 
            micaceous, very fined grained heavy minerals sparsely present; shells 
            moderately to abundantly present (mostly Mulinia and some oyster).  Present 
            only in subsurface of the map area (see cross section).  Auger hole CH 15 
            include typical sections.  Unit up to 33 ft (10 m) thick. Shown only in 
            cross section.

.122 Qpf - Penholoway Formation (Pleistocene, between 730 and 970 ka).  Fossiliferous sand 
           facies. Quartz sand, medium gray (N5) to  medium bluish gray (5B 5/1) or 
           greenish gray (5G6/1), fine to medium grained, phosphatic, bioturbated.  
           Dominant clay  minerals are kaolinite, illite/smectite, and illite in decreasing 
           order of abundance.  Unweathered beds contain a moderately diverse molluscan 
           fossil fauna, so this unit probably formed as a shallow-marine-shelf deposit.  
           Basal contact often marked by a layer 1 to 3 in (3-8 cm) thick of course-grained 
           sand and black phosphate pebbles.  Shown only in cross section.

.181 Qdc - Daniel Island Beds (informal) (Pleistocene, between 730  and 1,600 ka).  
           Clayey sand, silty to clayey sand, and clay, fine to medium grained, dark 
           bluish gray (5B 3/1) to dark gray (N3), dense; clay rich beds sticky; 
           interbeds of dark brownish  gray (5YR 3/1) peat.  Probably deposited in 
           estuarine to lagoonal environments.  Present only in subsurface channels 
           (see cross section).  Unit up to 60 ft (18 m) thick regionally.  
           Shown only in cross section.

.383 Tgc - Goose Creek Limestone (Pliocene, about 3.5 Ma).  Quartzose and phosphatic, 
           calcarenite, very pale orange (10YR 8/2) (wet) to chalky white (N9) (dry), 
           medium to coarse grained, sparsely shelly. Dominant clay minerals are kaolinite, 
           illite/smectite.  Basal contact marked by a layer 1 to 4 in (3 - 10 cm) thick 
           of black rounded phosphate pebbles 1 to 2 in. (3 - 5 cm) in diameter. 
           Unit up to 50ft (15 m) thick.  Shown only in cross section.

.391 Tmh - Marks Head Formation (Miocene, about 18 Ma).  Quartz-phosphate sand, 
           grayish olive (10YR 4/2) or olive gray (5YR 3/2) to moderate olive brown 
           (5YR 4/4), fine grained; contains attapulgite.  Basal contact with 
           underlying Ashley Formation (Ta) typically marked by sparse, subrounded 
           phosphate pebbles and (or) rounded fragments of thick oyster shells 0.5 to 
           1.0 in (1-3 cm) in diameter.  Vertebrate remains locally abundant.  
           Auger hole CH 14 inlcudes a typical section.  Unit up to 50 ft (15 m) thick 
           regionally.  Shown only in cross section.

.381 Ta - Ashley Formation of the Cooper Group (Oligocene, about 30 Ma). Calcarenite, 
          light olive brown (5Y 5/6), fine grained, phosphatic, massive.  Dominant clay 
          material is illite/smectite with lesser amounts of sepiolite and attapulgite.  
          Base of unit contains densely packed phosphate pebble bed 1 to 4 in. (3-10 cm) 
          thick, with pebbles 1 to 2 in. (3-5 cm) in diameter.  Sparsely macrofossiliferous 
          but sand sized foraminifera tests are abundant.  Auger hole CH 11 includes a 
          typical section.  Unit up to 125 ft (38 m) thick regionally.  Shown only in 
          cross section.

.41 Tpf - Parkers Ferry Formation of the Cooper Group (Eocene, about 38 Ma).  Calcilutite
          to very fined grained calcarenite, light blue green (5BG 6/6) to moderate yellow,
          stiff to plastic, dense, sticky.  Dominant clay mineral is illite/smectite; 
          lesser amounts of clinoptilolite.  Basal 1 to 2 ft (0.3-0.6 m) of unit often 
          black (N1) and composed mostly of phosphate and glauconite sand.  Contains 
          numerous short echinoid spines 0.25 to 0.50 in. (0.6-1.3 cm) long.  Unit up to 
          70 ft (21 m) thick regionally.  Shown only in cross section.