LOCATION SMITHWICK TXEstablished Series
TAXONOMIC CLASS: Very-fine, mixed, superactive, thermic Vertic Haplustepts
TYPICAL PEDON: Smithwick clay--rangeland.
(Colors are for dry soil unless otherwise stated.)
A1--0 to 5 inches; grayish brown (2.5Y 5/2) clay, dark
grayish brown (2.5Y 4/2) moist; moderate very fine subangular
blocky structure; hard, firm; many fine and very fine roots; about
5 percent siliceous pebbles; about 10 percent of soil surface is covered with chert, limestone, and quartz pebbles and cobbles; calcareous; moderately alkaline; clear wavy boundary. (2 to 8
inches thick)
B21--5 to 11 inches; light brownish gray (2.5Y 6/2) clay, grayish brown (2.5Y 5/2) moist; moderate medium and coarse blocky structure parting to moderate very fine blocky; very hard, very
firm; few very fine roots; few pressure faces; few siliceous
pebbles; calcareous; moderately alkaline; gradual wavy boundary.
(4 to 8 inches thick)
B22--11 to 21 inches; light yellowish brown (2.5Y 6/4) clay, light olive brown (2.5Y 5/4) moist; moderate fine and medium
blocky structure; very hard, very firm; few very fine roots;
common pressure faces; few very fine calcium carbonate
concretions; calcareous; moderately alkaline; gradual wavy
boundary. (6 to 14 inches thick)
B3--21 to 34 inches; light olive gray (5Y 6/2) clay, olive
gray (5Y 5/2) moist; common medium distinct yellow (5Y 7/6)
mottles; pale olive (5Y 6/3) stains on faces of peds; moderate
fine blocky and platy structure; very hard, very firm; few very
fine roots; few calcium carbonate concretions; calcareous;
moderately alkaline; gradual smoooth boundary. (8 to 15 inches thick)
Cr--34 to 65 inches; olive gray (5Y 5/2) shale, olive gray
(5Y 4/2) moist; neutral.
TYPE LOCATION: San Saba County, Texas; from the junction of U. S. Highway 190 and Texas Highway 16 in San Saba, west 4.3 miles on U. S. Highway 190, then 5.3 miles southwest on Farm Road 2732, 0.5
miles south on private road, 0.5 mile northwest along trail, then
330 feet south in range.
RANGE IN CHARACTERISTICS: Solum thickness ranges from 24 to 40 inches. When dry these soils have cracks as much as 1 to 3.5 cm
wide that extend from the surface to a depth of 20 inches or more. Clay content ranges from 60 to 80 percent in the 10 to 40 inch control section. Siliceous pebbles and cobbles cover from a few
to about 15 percent of the surface. Cobbles comprise less than 50 percent of the coarse fragments.
The A horizon has a hue of 10YR or 2.5Y, value of 4 through 6, and chroma of 2 through 4. Clay content ranges from 55 to 75 percent.
The B2 horizon has a hue of 2.5Y or 5Y, value of 5 through 7, and chroma of 2 through 4. The B2 horizons contain from 0 to 3
percent cobbles and from 0 to 3 percent pebbles.
The B3 horizon has a hue of 2.5Y or 5Y, value of 5 or 6, and
chroma of 2 through 4. Concretions and soft masses of calcium carbonate range from a few to about 5 percent by volume. The B3 horizons contain from 0 to 3 percent cobbles and from 0 to 3
percent pebbles.
The Cr horizon has a hue of 2.5Y or 5Y, value of 4 through 6, and chroma from 0 through 4. This is neutral through moderately
alkaline shale, very shaly clay or shaly clay. This material can
be dug with a spade.
COMPETING SERIES: There are no competing series in the same
family. Other competing series include the
Boro,
Brackett,
Chargo,
Denhawken,
Ellis,
Leeray,
Mangum,
Owens,
Runn,
Throck, and
Vernon series. All these soils have less than 60 percent clay in their control sections. In addition, Boro soils have mean annual temperatures of less than 59 degrees F.; Brackett soils have more than 40 percent calcium carbonate equivalent; Chargo and Runn
soils have mean annual temperature of more than 72 degrees F; Denhawken soils have mean annual temperatures of more than 72
degrees F.; Ellis soils are moist in the moisture control section
for longer periods; Leeray soils have sola thicker than 40 inches
and have intersecting slickensides; Mangum soils formed in recent alluvial sediments; Owens soils have sola thinner than 20 inches;
and Vernon soils have hues of 5YR or redder.
GEOGRAPHIC SETTING: Smithwick soils are on strongly sloping to
steep hillsides in hilly topography. Surfaces are plane to
strongly convex with slopes of 8 to 45 percent, averaging about 20 percent. At the type location, the soil formed in residuum from Smithwick shale of the Atoka epoch of the Pennsylvanian period.
Mean annual temperature ranges from 64 degrees to 72 degrees F.; average annual precipitation ranges from 25 to 30 inches; and Thornthwaite annual P-E indices range from 40 to 52.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the
Cho,
Frio,
Nukrum,
Nuvalde, and
Tarpley series. All these soils except Tarpley have less than 60 percent clay in their control sections. Tarpley soils are on higher lying plateaus and have a lithic contact with
limestone at depths of 10 to 20 inches. Cho soils are on high
lying ridges and are underlain by cemented caliche at depths of
less than 20 inches. Nukrum soils are on footslopes as valley
fill, have mollic epipedons and sola more than 40 inches thick. Nuvalde soils are on ancient terraces and have a mollic epipedon. Frio soils have thick mollic epipedons and are on flood plains.
DRAINAGE AND PERMEABILITY: Well drained; medium to rapid runoff; very slow permeability.
USE AND VEGETATION: Used entirely for range. Native vegetation
is mostly mid and short grasses, consisting of sideoats grama, vine-mesquite, silver bluestem, buffalograss, Arizona cottontop, Texas needlegrass, curlymesquite, and white tridens. Mesquite and thorny shrubs invade most of the areas of this soil.
DISTRIBUTION AND EXTENT: Central Texas. The series is of minor extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Temple, Texas
SERIES ESTABLISHED: San Saba County, Texas; 1980.
REMARKS: This soil would have been classified in the Grumosol
great soil gruop.
ADDITIONAL DATA: Texas Highway Department Data, sample numbers R-75-125, R-75-126-R. NSSL sample RT79-TX011 on texture and mineralogy.