LOCATION OPLIN                   TX

Established Series


The Oplin series consists of very shallow and shallow, well drained, moderately permeable soils formed in residuum from indurated limestone. These upland soils have slopes that range from 1 to 40 percent.

TAXONOMIC CLASS: Loamy-skeletal, carbonatic, thermic Lithic Calciustolls

TYPICAL PEDON: Oplin very flaggy clay loam--native rangeland. (Colors are for dry soil unless otherwise stated).

A--0 to 3 inches; brown (10YR 5/3) very flaggy clay loam, dark brown (10YR 3/3) moist; moderate fine granular structure; hard, friable; many fine roots; common wormcasts; about 40 percent surface cover of cobblestone and gravel size fragments of limestone; 25 percent limestone fragments of pebble size and 25 percent flagstones; violently effervescent; moderately alkaline; clear irregular boundary. (2 to 10 inches thick)

Bk--3 to 9 inches; brown (10YR 5/3) very flaggy clay loam, dark brown (10YR 3/3) moist; moderate fine granular structure; hard, friable; many fine roots; common wormcasts; 65 percent limestone fragments, of which 20 percent are pebble size and 45 percent are flagstone size; pendants and coatings of calcium carbonate on lower side of limestone fragments; violently effervescent; moderately alkaline; abrupt wavy boundary. (4 to 10 inches thick)

R/Bk--9 to 15 inches; fractured and layered, limestone bedrock with a thin discontinuous cemented cap which extends into cracks in the limestone; secondary calcium carbonate coatings on rocks that partially plug the seams; diffuse boundary. (0 to 8 inches thick)

R--15 to 30 inches; fractured, platy and indurated limestone bedrock.

TYPE LOCATION: Callahan County, Texas; from the intersection of Texas Highways 206 and 36 in Cross Plains, 4.0 miles north on Texas Highway 206, then 1.5 miles north and west on a county road to its junction with another county road, then 2.8 miles north on county road, and 50 feet west in rangeland.

RANGE IN CHARACTERISTICS: Solum thickness and depth to limestone bedrock ranges from 7 to 20 inches. The control section contains from 35 to 80 percent fragments of limestone that are mostly less than 10 inches across the long axis.

The A and Bk horizons have hue of 7.5YR and 10YR, values of 3 through 5, and chromas of 2 or 3. The fine-earth fraction is loam, silty clay loam, or clay loam with a clay content of 20 to 35 percent. Coarse fragments range from 15 to 65 percent in the A horizon and from 50 to 80 percent in the Bk horizon. Most fragments in the Bk horizon have pendants of calcium carbonate on the lower side. Calcium carbonate content ranges from 10 to 30 percent in the fine-earth fraction and total calcium carbonate content is 40 to 60 percent.

The R layer is indurated limestone. It is layered and fractured and has secondary calcium carbonate coatings in the upper part.

COMPETING SERIES: These are the Aledo, Altuda, Ector, and Lueders series. A similar soil is the Langtry series. Aledo, Altuda, Ector and Langtry soils are dry in the control section for longer periods of time. In addition, Langtry soils are in the hyperthermic family. Lueders soils occur in areas with slightly cooler temperatures, have different rangeland vegetation, and formed mainly from limestones of Permian origin.

GEOGRAPHIC SETTING: Oplin soils are on convex limestone ridgetops and breaks of erosional uplands. Slopes are mainly 1 to 15 percent, but some are as much as 40 percent. These soils formed in residuum over indurated limestone of the Cretaceous period. Mean annual precipitation ranges from 22 to 30 inches, and mean annual air temperature ranges from 64 degrees to 70 degrees F. Frost free days ranges from 210 to 235 days, and elevation ranges from 1,200 to 2,400 feet. Thornthwaite annual P-E indices ranges from 32 to 44

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Brackett, Hext, Kavett, Nuvalde, Speck, Tarrant, and Valera series. Brackett soils contain less than 35 percent coarse fragments in the control section and are on hillsides. Hext and Nuvalde soils have sola more than 20 inches thick. In addition, the Hext soils are on upland ridges and Nuvalde soils are in valleys. Kavett soils are on divides. Speck soils occur on nearly level and gently sloping areas and have clayey Bt horizons. Tarrant soils have more than 35 percent clay on similar positions. Valera soils are on divides, are more clayey, have less than 35 percent coarse fragments in the control section, and have sola more than 20 inches thick.

DRAINAGE AND PERMEABILITY: Well drained. Permeability is moderate. Runoff is very low on 1 to 3 percent slopes, low on 3 to 5 percent slopes, medium on 5 to 20 percent slopes and high on 20 to 40 percent slopes.

USE AND VEGETATION: Used for rangeland. Vegetation consists of sideoats grama, little bluestem, slim tridens, silver bluestem, fall witchgrass, and juniper and live oak trees. Traces of Englemann-daisy, vine ephedra, and bush sunflower occur on most sites.

DISTRIBUTION AND EXTENT: Central Texas, mainly in the eastern part of the Edwards Plateau. The series is of moderate extent.


SERIES ESTABLISHED: Callahan County, Texas; 1979.

REMARKS: The Oplin series was proposed for soils previously considered part the Ector series. These soils are in more moist areas with over 20 inches annual precipitation. Oplin differs from Leuders by some chemical differences not yet measured, because there is a difference in vegetation types, especially woody species.

The series is in the active cation exchange activity class. Diagnostic horizons or features recognized in this pedon are:

Mollic epipedon - 0 to 9 inches. (A and Bk horizons)

Calcic horizon - 3 to 9 inches. (Bk horizon)

Lithic contact - at 9 inches.

Soil Interpretation Record No: TX0890

National Cooperative Soil Survey