Established Series


The Oakhurst series consists of soils that are deep to unconsolidated volcanic tuff. They are moderately well drained, very slowly permeable soils on uplands. They formed in slightly acid to alkaline clayey tuffaceous materials that overlie siltstone and sandstone strata. Slopes are mainly about 2 percent, but range from 1 to 8 percent.

TAXONOMIC CLASS: Fine, smectitic, thermic Vertic Hapludalfs

TYPICAL PEDON: Oakhurst very fine sandy loam on 2 percent slope, in pasture. (Colors are for moist soil unless otherwise stated.)

A--0 to 5 inches; dark gray (10YR 4/1) very fine sandy loam, gray (10YR 5/1) dry; weak fine granular structure; friable; slightly sticky and nonplastic; many fine roots; strongly acid; clear smooth boundary. (2 to 7 inches thick)

E--5 to 7 inches; grayish brown (10YR 5/2) very fine sandy loam, light brownish gray (10YR 6/2) dry; few fine distinct dark yellowish brown mottles; weak fine granular structure; friable, nonsticky and nonplastic; many fine roots; strongly acid; abrupt wavy boundary. (2 to 8 inches thick)

Bt1--7 to 20 inches; dark grayish brown (10YR 4/2) clay, grayish brown (10YR 5/2) dry; few fine distinct mottles of yellowish brown (10YR 5/4) and light gray (10YR 7/2) mottles; moderate medium coarse angular blocky structure; extremely hard, very firm, sticky and plastic; many fine roots; few fine pores; distinct clay films on faces of peds that are 1 unit of value darker than crushed peds; vertical cracks about 2 cm wide extend through horizon; few fine black concretions; strongly acid; gradual wavy boundary. (10 to 20 inches thick)

Bt2-- 20 to 46 inches; gray (10YR 5/1) clay, light gray (10YR 6/1) dry; common medium distinct yellowish brown (10YR 5/4) and pale olive (5Y 6/4) mottles; weak coarse angular blocky structure; extremely hard, very firm, sticky and plastic; few fine roots, few fine pores; distinct clay films on faces of peds; few small slickensides; cracks extend downward from horizon above; few black streaks on some faces of peds and along crack; few fine black concretions; medium acid; gradual wavy boundary. (10 to 30 inches thick)

C--46 to 65 inches; light gray (10YR 6/1) silty clay loam, light gray (10YR 7/1) dry; massive, extremely hard, very firm; few fine roots, unconsolidated volcanic tuff, mildly alkaline.

TYPE LOCATION: San Jacinto, County, Texas; from intersection of U.S. 190 and Farm Road 946 in Oakhurst; 3.8 miles north on Farm Road 946; 100 feet west of road in pasture. Latitude: 30 degrees, 47 minutes, 30 seconds N; Longitude: 95 degrees, 18 minutes, 00 seconds W.

RANGE IN CHARACTERISTICS: Solum thickness ranges from 40 to 60 inches. Siliceous pebbles range from none to few throughout the pedon. COLE is greater than 0.09 in the argillic horizon and the soil has a potential linear extensibility of 6 cm or more the in the upper meter. The clay content decreases 20 to 30 percent in the lower part of the solum or the C horizon is encountered within 60 inches of the surface.

The A horizon averages less than 10 inches thick in more than 50 percent of the pedon, but ranges up to 15 inches thick in subsoil troughs. It has hue of 10YR or 2.5Y, value of 3 to 6 and chroma of 1 or 2 moist.

The E horizon has hue of 10YR, value of 5 to 7, and chroma 1 or 2. The A and E horizons have textures of silt loam, fine sandy loam, very fine sandy loam, or loamy very fine sand. Reaction ranges from strongly acid to slightly acid. The boundary between the A and Bt horizon is abrupt, and is wavy or irregular.

The Bt horizon has hue of 10YR or 2.5Y, value of 4 to 6 and chroma of 1 or 2. Mottles range from few to common in shades of brown, yellow, and olive. Texture is clay, silty clay, silty clay loam, or clay loam with clay content ranging from 35 to 50 percent. The Bt1 horizon ranges from very strongly acid to slightly acid, and the Bt2 horizon ranges from medium acid to mildly alkaline. Some pedons have BC horizons that range from slightly acid to moderately alkaline.

The C horizon has hue of 10YR or 2.5Y, value of 5 to 7 and chroma 1 or 2. Texture is clay, silty clay loam, clay loam or sandy clay loam. Some pedons contain concretions of calcium carbonate and crystals of gypsum. Reaction ranges from slightly acid to moderately alkaline. Though not diagnostic, soft siltstone and sandstone are common below 40 inches.

COMPETING SERIES: These are the Colbert (AL), Eastwood (TX), Etoile (TX), Kipling (MS), Lorman (MS), Oula (LA), Rayburn (TX), Wilcox (MS), and Woodtell (TX) series. Colbert soils are underlain by limestone bedrock and formed in residuum weathered from argilliceous limestone. Eastwood soils are more acid and receive more rainfall. Etoile soils are less acid throughout and contain free carbonates in the C horizon. Kipling and Wilcox soils do not have abrupt textural changes between the A or E and Bt horizon. Lorman soils have a more clayey C horizon. Oula soils do not have distinct mottling in the argillic horizon and are well drained. Rayburn soils have a paralithic contact of tuffaceous sandstone and clays. Woodtell soils have redder upper Bt horizons.

GEOGRAPHIC SETTING: Oakhurst soils are on nearly level to sloping uplands. Some areas are in slight depressions. Slopes are mainly about 2 percent but range from 1 to 8 percent. Oakhurst soils formed in slightly acid to moderately alkaline clayey sediments that overlie tuffaceous siltstone and sandstone strata. Mean annual precipitation ranges from 40 to 50 inches and mean annual temperature ranges from 65 to 70 degrees F. Frost free days range from 220 to 260 days and elevation ranges from 200 to 500 feet. Thornthwaite annual P-E indices range from 70 to 80.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Annona, Corrigan, Falba, Rayburn, Waller, and Woodville soils. Annona, Rayburn, and Woodville soils are better drained, have higher chroma in the Bt horizon, and are on steeper slopes. Corrigan and Falba are 20 to 40 inches over a paralithic contact with tuffaceous siltstone and sandstone and are on nearly similar landscapes. Waller soils have fine-loamy control sections, have tongues of E material penetrating the Bt horizon, are poorly drained, and are in lower concave positions.

DRAINAGE AND PERMEABILITY: Moderately well drained. Permeability is very slow. Runoff is medium to high. These soils are saturated in the upper Bt for short periods in the spring.

USE AND VEGETATION: This soil is used mainly for pasture and forest. A few areas are farmed to soybeans and grain sorghum. Native vegetation is mixed pine and hardwood forest with an understory of grasses and shrubs.

DISTRIBUTION AND EXTENT: Mainly in east central and east Texas. The series are moderately extensive.


SERIES ESTABLISHED: San Jacinto County, Texas; 1983.

REMARKS: These soils do not have an aquic moisture regime. Classification change from Vertic Albaqualfs to Vertic Hapludalfs based on interpretation that low chroma mottles are predominantly the result of weathering of gray (low chroma) parent materials. These soils were formerly mapped with the Anacoco or Lufkin series.

Diagnostic horizons and features recognized in this pedon are:

Ochric epipedon - 0 to 7 inches (A and E horizons)

Albic horizon - 5 to 7 inches (E horizon)

Argillic horizon - 7 to 46 inches (Bt horizons)

Vertic feature - COLE greater than 0.09

National Cooperative Soil Survey