LOCATION FRIO TXEstablished Series
TAXONOMIC CLASS: Fine, smectitic, thermic Cumulic Haplustolls
TYPICAL PEDON: Frio silty clay--wooded (Colors are for dry soils unless otherwise stated.)
A1--0 to 8 inches; dark grayish brown (10YR 4/2) silty clay, very dark grayish brown (10YR 3/2) moist; moderate fine and medium granular structure; hard, firm; many fine, medium, few coarse roots; strong effervescence; moderately alkaline; clear smooth boundary.
A2--8 to 22 inches; dark grayish brown (10YR 4/2) clay loam, very dark grayish brown (10YR 3/2) moist; moderate medium and coarse subangular blocky structure parting to moderate fine subangular blocky; hard, firm; many fine, medium, and few coarse roots; few fine shell fragments; strong effervescence; moderately alkaline; clear smooth boundary.
A3--22 to 29 inches; dark grayish brown (10YR 4/2) silty clay loam, very dark grayish brown (10YR 3/2) moist; moderate fine and medium prismatic structure parting to moderate fine and medium subangular blocky; hard, firm; common fine, medium, and few coarse roots; common fine films and threads of calcium carbonate; few fine shell fragments; strong effervescence; moderately alkaline; gradual smooth boundary.
A4--29 to 40 inches; dark grayish brown (10YR 4/2) silty clay loam, very dark grayish brown (10YR 3/2) moist; moderate fine and medium prismatic structure parting to moderate medium and coarse subangular blocky; hard, firm; common fine, medium, and few coarse roots; common fine films and threads of calcium carbonate; strong effervescence; moderately alkaline; gradual smooth boundary. (Combined A horizons are 20 to 60 inches thick)
Bk--40 to 80 inches thick; grayish brown (10YR 5/2) silty clay, dark grayish brown (10YR 4/2) moist; moderate medium and coarse prismatic structure parting to weak coarse blocky; hard, firm; few fine, medium, and coarse roots; many fine films and threads and a few soft masses of calcium carbonate; strong effervescence; moderately alkaline.
TYPE LOCATION: Coryell County, Texas; approximately 18 miles southeast of Gatesville, Texas. About 5.2 miles northeast of the intersection of Texas Highways 36 and 236, along Texas Highway 236; then 100 feet west of pavement in wooded area. This site is about 0.28 mile northeast of the north end of the Leon River bridge in Mother Neff State Park.
RANGE IN CHARACTERISTICS: Depth to sand, gravel, or limestone ranges from 6 to about 30 feet. The clay content ranges from 30 to about 50 percent but the control section averages 35 to 42 percent clay. The calcium carbonate equivalent ranges from 15 to 40 percent. The COLE ranges from about .04 to .09 in the upper 50 inches but lacks a layer 20 inches or more thick with COLE OF .07 or more. Some pedons contain limestone and chert pebbles or cobbles that make up less than 15 percent by volume.
The A horizon has hue of 7.5YR or 10YR, value of 3 to 5, and chroma of 2 or 3. Texture is silty clay, silty clay loam, or clay loam. Some pedons have light colored discontinuous loamy strata less than 3 inches thick.
Most pedons have a B horizon with greater value or chroma than the A horizon. It is below a depth of 22 inches and typically below the control section. However, some pedons have buried A horizons at these depths. The soil material above the buried A horizon is probably post-settlement alluvium.
COMPETING SERIES: There are no competing series in the family. Other competing soils are Bosque, DeLeon, Lewisville, Oakalla, Port, and Rioconcho series. Bosque, Lewisville, Oakalla, and Port soils have control sections with less than 35 percent silicate clay. In addition, Lewisville soils have a mollic epipedon less than 20 inches thick. Oakalla soils have a mollic epipedon less than 20 inches thick and have carbonatic mineralogy. DeLeon and Rioconcho soils have vertic properties. Also, Rioconcho soils are dry for longer periods.
GEOGRAPHIC SETTING: Frio soils are on flood plains of major streams. These soils formed in calcareous loamy and clayey alluvium. The alluvium derived mainly from soils that formed in limestone of Cretaceous age. The slopes are commonly less than 1 percent but range to 2 percent. The climate is moist subhumid. Mean annual precipitation ranges from 25 to 36 inches; mean annual temperature is 64 to 68 degrees F.; Frost free days range from 220 to 260 and elevation ranges from 400 to 1700 feet above sea level. The Thornthwaite P-E indices range from 38 to 56.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Bosque, DeLeon, and Lewisville series. Adjacent upland series include the Denton, Doss, Real, and Slidell. Bosque and DeLeon soils are on similar positions. Lewisville soils are on terraces above the Frio soils. Denton and Slidell soils are clayey, cracking soils. Doss and Real soils are shallow, loamy soils.
DRAINAGE AND PERMEABILITY: Well drained; slow runoff; moderately slow permeability. Most areas have ground water within a depth of 20 feet. The soil floods unless protected, as seldom as once in about 10 years and as often as one to three times a year.
USE AND VEGETATION: Used for pasture, cropland, and range. Principal crops are small grain, corn, and grain sorghum. In the western part it is used mostly for rangeland. In the eastern part, native vegetation is mainly an open-canopied deciduous forest of pecan, elm, and oak; in the western part open prairie with a few pecan and elm trees near the stream channel. The main grasses are big and little bluestem, switchgrass, indiangrass, Texas wintergrass, and Virginia wildrye.
DISTRIBUTION AND EXTENT: Mainly in Texas, occurring primarily in the Grand Prairie, and eastern part of the Edwards Plateau and to a lesser extent in the Blackland Prairies and Cross Timbers LRA's The series is of large extent.
MLRA OFFICE RESPONSIBLE: Temple, Texas
SERIES ESTABLISHED: Reconnaissance Survey of Southwest Texas; 1911.
REMARKS: The control section averages 34.1 percent silicate clay and 35.6 percent total clay. We elect to classify this series in a fine family.
Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - 0 - 40 inch zone.
Cambic horizon - 40 - 80 inch zone.
ADDITIONAL DATA: NSSL-Coryell County, Texas S80TX-99-003 (81P510-515).