LOCATION CALLAHAN           TX

CALLAHAN SERIES

The Callahan series consists of moderately deep, well drained, slow permeable soils that formed in clayey shale interbedded with thin sandstone strata. These soils are on gently to strongly sloping plains. Slopes range from 1 to 12 percent.

TAXONOMIC CLASS: Fine, mixed, active, thermic Typic Haplustalfs

TYPICAL PEDON: Callahan loam--cultivated. (Colors are for dry soil unless otherwise stated.)

Ap--0 to 7 inches; reddish brown (5YR 4/4) loam, dark reddish brown (5YR 3/4) moist; massive; hard, firm; few fine roots; few fine pores; surface has 1/4 inch crust that is very hard; moderately alkaline; clear smooth boundary. (1 to 10 inches thick)

Bt--7 to 18 inches; reddish brown (5YR 4/3) clay, dark reddish brown (5YR 3/3) moist; compound moderate, medium prismatic structure, parting to moderate fine blocky structure; very hard, very firm; few fine roots; few fine pores; thin patchy clay films on faces of peds that are one- half value darker than the inside of the peds; few fine pebbles of quartz; moderately alkaline; clear smooth boundary. (7 to 18 inches thick)

Btk--18 to 30 inches; reddish brown (5YR 4/4) clay, dark reddish brown (5YR 3/4) moist; moderate fine blocky structure; very hard, very firm; few fine roots; few fine pores; the surfaces of the peds are shiny; few fine pebbles of quartz; few films and threads of calcium carbonate; few strongly and weakly cemented concretions of calcium carbonate; slight effervescence; moderately alkaline; gradual wavy boundary. (8 to 20 inches thick)

Btk/C--30 to 36 inches; yellowish red (5YR 5/6) clay, yellowish red (5YR 4/6) moist; weak medium blocky structure; very hard, firm; few thin patchy clay films on faces of peds; 10 percent by volume of partially weathered fragments of shale; few strongly and weakly cemented concretions of calcium carbonate; strong effervescence; moderately alkaline; clear smooth boundary. (0 to 10 inches thick)

Cdk--36 to 70 inches; thin lenses and strata of pink, claystone bedrock, interbedded with weakly cemented sandstone and yellow clay loam; massive; extremely hard, very firm; cleavage planes and horizontal bedding are evident; few concretions of calcium carbonate and few soft bodies of calcium carbonate; strong effervescence; moderately alkaline.

TYPE LOCATION: Coleman County, Texas; about 15 miles south, 61 degrees east of the Coleman County Courthouse at a point in a cultivated field that is 150 feet south of U. S. Highway 84 and 67, and 0.2 mile west of the Brown-Coleman County Line post on U. S. Highway 84 and 67.

RANGE IN CHARACTERISTICS: The solum is 20 to 40 inches thick. Calcium carbonate in the form of films, threads, soft bodies and concretions occur at depths of 18 to 28 inches below the surface. Coarse fragments of siliceous pebbles, sandstone fragments, and concretions range from a few to about 10 percent by volume. Reaction ranges from neutral to moderately alkaline in the A and upper Bt horizons and from mildly to moderately alkaline in the lower part of the solum.

The A horizon has hue of 5YR to 10YR, value of 4 to 6, and chroma of 2 to 4. Soils with values and chromas of less than 3.5 have A horizons less than 8 inches thick. The A horizon is loam, sandy clay loam, clay loam or their stony or cobbly counterparts.

The Btk and Btk/C horizons have hue of 2.5YR to 7.5YR, value of 3 to 7, and chroma of 3 to 6. They are clay or clay loam, and range in clay content from 35 to
50 percent.

The Cd layer is claystone bedrock or dense clay that is commonly interbedded with thin strata of sandstone and alkaline loamy or clayey sediments.

COMPETING SERIES: These are the Bluegrove, Bonti, Lindale, Menard, Pedernales, Thurber, Travis, Truce, Wichita, Windthrost, and Winters series. Bluegrove, Bonti, Pedernales, Travis, Truce, Windthorst, and Winters soils lack secondary carbonates within 28 inches of the surface. In addition, Bonti and Travis soils have less than 75 percent base saturation. Lindale, Pedernales, Truce, Windthorst, and Winters soils lack a paralithic contact within 40 inches of the surface. Menard soils have Bt horizons with less than 35 percent clay. Thurber soils have montmorillonitic mineralogy. Wichita soils have sola thicker than 40 inches.

GEOGRAPHIC SETTING: Callahan soils are on gently sloping to strongly sloping plains flanked by receding esacrpments of claystone and sandstone of lower Permian and upper Pennsylvanian age. Slopes range from 1 to 12 percent and are dominantly about 2 percent. The soil formed in reddish clay loam, or clay residuum over claystone and weakly cemented sandstone bedrock several feet thick. The climate is dry subhumid with a mean annual precipitation of 24 to 30 inches. Elevation ranges from 850 to 2300 feet and Frost Free period ranges from 220 to 250 days. Thornthwaite annual P-E index of 32 to 44, and mean annual air temperature of 64 to 67 degrees F.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Bonti, Truce, and Winters series, and the Owens and Throck series. Owens soils have sola less than 20 inches thick; and, in addition, Owens and Throck soils lack argillic horizons.

DRAINAGE AND PERMEABILITY: Well drained; high runoff on slopes 1 to 5 percent slopes and very high runoff on slopes 5 to 12 percent slopes; slow permeability.

USE AND VEGETATION: Used for cultivation and rangeland. Cultivated crops are mostly small grains and grain sorghum. Native vegetation consists mostly of curlymesquite, buffalograss, and Texas wintergrass with a few scattered hackberry, post oak, and mesquite trees.

DISTRIBUTION AND EXTENT: Mainly in Central Texas, in the southern part of the North Central Prairies and Rolling Red Plains. The series is of moderate extent.

MLRA OFFICE RESPONSIBLE: Temple, Texas

SERIES ESTABLISHED: Coleman County, Texas; 1968.

REMARKS: Callahan soils were formerly included in the Windthorst series.

Diagnostic horizons and features recognized in this pedon:

Ochric epipedon - 0 to 7 inches

Argillic horizon - the zone from 7 to 36 inches.

Densic material - occurs at 36 to 70 inches.