Established Series
Rev. CLG


The San Antonio series consists of deep, well drained, slowly permeable soils formed in ancient alluvial sediments. These soils are on nearly level to gently sloping uplands and stream terraces. Slopes range from 0 to 5 percent.
TAXONOMIC CLASS: Fine, smectitic, hyperthermic Typic Haplustalfs

TYPICAL PEDON: San Antonio clay loam - cropland.
(Colors are for dry soil unless otherwise stated.)

Ap--0 to 8 inches; dark brown (10YR 4/3) clay loam, dark brown (10YR 3/3) moist; weak medium subangular blocky structure when moist; very hard and massive when dry, firm, sticky; 1 to 2 percent pebble size iron and chert fragments on the surface; slightly acid, abrupt smooth boundary. (6 to 15 inches thick)

Bt--8 to 20 inches; dark reddish brown (5YR 3/2) clay; dark reddish brown (5YR 2/2) moist; strong medium blocKy structure; extremely hard, very firm, very sticky; thin continuous clay films; cracks 1/8 to 1/4 inches wide in upper 10 inches filled with soil from above; slightly acid, clear smooth boundary (8 to 14 inches thick)

Btk--20 to 28 inches; Reddish brown (5YR 4/4) clay; dark reddish brown (5YR 3/4) moist; weak medium blocky structure; extremely hard, firm, sticky; thin discontinuous clay films; few fine concretions and soft masses of calcium carbonate; calcareous, moderately alkaline; gradual smooth boundary. (8 to 14 inches thick)

Bk--28 to 42 inches; light yellowish brown (10YR 6/4) clay loam, yellowish brown (10YR 5/4) moist; few fine faint reddish yellow and brown mottles; weak medium subangular blocky structure; hard, firm, sticky; an estimated 7 percent by volume of concretions and soft masses of calcium carbonate; calcareous; moderately alkaline; gradual smooth boundary. (10 to 16 inches thick)

Ck--42 to 60 inches; very pale brown (10YR 7/4) clay loam, light yellowish brown (10YR 6/4) moist; few fine distinct mottles of reddish yellow and brown; massive; an estimated 5 percent by volume of concretions and soft masses of calcium carbonate; few fragments of sandstone; calcareous; moderately alkaline.

TYPE LOCATION: Bexar County, Texas. Approximately 9 miles southeast of the courthouse in San Antonio. One half mile south of Boldtville on Foster road, then west one half mile on Lodi road, in cultivated field 75 yards west of Lodi road.

RANGE IN CHARACTERISTICS: Solum thickness ranges from 40 to 60 inches. Depth to secondary calcium carbonate ranges from 18 to 28 inches.

The A horizon is dark brown (7.5YR 4/2; 10YR 4/3), dark grayish brown (10YR 4/2), or very dark grayish brown (10YR 3/2). It is dominantly clay loam, but is sandy clay loam or loam.

The Btk horizon is dark reddish brown (5YR 3/2, 2/2, 3/3), dark brown (7.5YR 4/2, 3/2), or reddish brown (5YR 4/3). The Bt and Btk horizons are clay loam or clay with a clay content of 35 to 50 percent. The Bt horizon is slightly acid through moderately alkaline. The Btk horizon is reddish brown (5YR 5/4, 4/4), brown (7.5YR 5/2, 5/4), light yellowish brown (10YR 6/4), or reddish yellow (7.5YR 6/6) and some pedons have a few faint brownish or yellowish mottles. It is mildly or moderately alkaline. The C horizon is pink (5YR 7/3, 7/4), light reddish brown (5YR 6/3, 6/4), reddish yellow (7.5YR 7/6), light yellowish brown (10YR 6/4), or very pale brown (10YR 7/3, 7/4). It is clay loam or sandy clay loam.

In some pedons the C horizon has a few faint to distinct reddish brown and reddish yellow mottles. Sandstone fragments are few to common below about 40 inches.

COMPETING SERIES: There are no other series in the same family. Similar soils include the Floresville, Normangee and Webb series. Floresville and Webb soils have mixed mineralogy and secondary forms of calcium carbonate occur at depths of more than 28 inches. Normangee soils have mean annual soil temperatures less than 72 degrees F.

GEOGRAPHIC SETTING: San Antonio soils are on nearly level to gently sloping, plain to slightly concave erosional uplands and stream terraces. Slope gradients dominantly range from 0 to 3 percent but are up to 5 percent. The soil formed in calcareous clay loams such as that of the Willis Point formation that are 6 to 10 feet thick over mudstone or sandstone. The climate is subtropical. The mean annual precipitation ranges from 25 to 36 inches; the Thornthwaite P-E index is about 36 to 44. The mean annual temperature ranges from 70 to 72 degrees F.

GEOGRAPHICALLY ASSOCIATED SOILS: These include Duval, Miguel, and Willacy soils. The Duval and Willacy soils have fine-loamy control sections. In addition, Willacy soils have friable epipedons when the soil is moist. The Miguel soils, as well as the Willacy soils have secondary calcium carbonate at depths below 28 inches. These soils occur on similar surfaces.

DRAINAGE AND PERMEABILITY: Well drained; slow runoff; slow permeability.

USE AND VEGETATION: Used mostly for rangeland. Small areas are used to grow grain sorghum and forage sorghum. Native vegetation includes little bluestem, fourflower trichloris, sideoats grama, buffalograss, mesquite, and sensitive briar.

DISTRIBUTION AND EXTENT: Occurs in the north central portion of the Rio Grande Plain and is moderately extensive.


SERIES ESTABLISHED: Bexar County, Texas, San Antonio area; 1904.

REMARKS: Diagnostic horizons and features recognized in this pedon are:

Ochric epipedon - 0 to 8 inches.

Argillic horizon - 8 to 28 inches.

Calcic horizon - 28 to 42 inches.

National Cooperative Soil Survey
U. S. A.