Established Series


The San Benito series is a member of the fine-loamy, mixed, thermic family of Calcic Pachic Haploxerolls. Typically, San Benito soils have dark grayish brown, neutral, clay loam A horizons and light yellowish brown, moderately alkaline, clay loam C horizons over shale at a depth of about 48 inches.

TAXONOMIC CLASS: Fine-loamy, mixed, superactive, thermic Calcic Pachic Haploxerolls

TYPICAL PEDON: San Benito clay loam - grassland. (Colors are for dry soil unless otherwise noted.)

A11--0 to 10 inches; dark grayish brown (10YR 4/2) clay loam, very dark grayish brown (10YR 3/2) moist; moderate fine subangular blocky structure that parts readily to moderate fine granular structure; very hard, firm sticky, plastic; many very fine roots; common very fine interstitial pores; neutral (pH 6.8); clear smooth boundary. (8 to 12 inches thick)

A12--10 to 28 inches; dark grayish brown (10YR 4/2) clay loam, very dark grayish brown (10YR 3/2) moist; moderate medium subangular blocky structure; very hard, firm, sticky, plastic; common very fine roots; few very fine interstitial and tubular pores; few fine pressure faces; neutral (pH 7.0); gradual smooth boundary. (12 to 18 inches thick)

C1ca--28 to 48 inches; light yellowish brown (10YR 6/4) clay loam, dark yellowish brown (10YR 4/4) moist; weak medium subangular blocky structure; hard, friable, sticky, plastic; common very fine roots; common very fine and fine tubular pores; lime disseminated and as coatings in pores and on some ped surfaces; moderately alkaline (pH 8.0); gradual smooth boundary. (8 to 30 inches thick)

C2--48 to 60 inches; yellowish brown, soft, calcareous sandy shale.

TYPE LOCATION: San Benito County, California; 5 miles north of San Benito; 1/2 mile west of Willow Creek Road, center part of sec. 8, T.15S., R.8E.

RANGE IN CHARACTERISTICS: Depth to a paralithic contact of soft shale, sandstone or consolidated sediments is 40 to 60 inches. The mean annual soil temperature at a depth of 20 inches is 60 degrees to 66 degrees F. The soil temperature usually does not go below 47 degrees F. Soil between the depths of about 4 and 12 inches is usually moist in some or all parts from some time in October or November until some time in May. The same soil zone usually is dry all the rest of the year. The soil is usually clay loam or silty clay loam with more than 15 percent fine sand or coarser. A few pedons are loam or silt loam. Vertical cracks 1/4 to 1/2 inch wide develop upon soil drying and extend from the surface to a depth of 20 inches or more. Pressure faces and a few non-intersecting slickensides are present in some pedons.

The dry A horizon is grayish brown, dark grayish brown, brown or dark brown in 10YR or 2.5Y hue and is very dark grayish brown or dark brown moist. Organic matter content is 1.5 to 4 percent in the upper 20 inches and exceeds 1 percent to a depth of as much as 30 inches. The A horizon has moderate or strong granular or subangular blocky structure. It is neutral or slightly alkaline, but is not calcareous in the upper part except where soils are mixed or overturned by rodents or tillage. This horizon is 20 to 30 inches thick.

The C horizon is grayish brown, light brownish gray, pale brown, light yellowish brown or yellowish brown. It is moderately alkaline and is calcareous in some part. This horizon has few to many lime segregations in some part which occur as small soft masses, veins, coatings or powder. Some pedons have a few clay films. Some discrete shale fragments are present in some pedons.

COMPETING SERIES: These are the Alo, Altamont, Ayar, Castaic, Gazos, Linne, Nacimiento, and Salinas series. Alo, Altamont, and Ayar soils have intersecting slickensides and clay texture. Castaic soils have ochric epipedons. Gazos soils are slightly and moderately acid. Linne soils have a chroma of less than 2. Nacimiento soils are calcareous throughout and have a mollic epipedon less than 20 inches thick. Salinas soils lack a paralithic contact and have a chroma of less than 2 in the A horizon.

GEOGRAPHIC SETTING: San Benito soils formed in residuum weathered from shale and sandstone with strongly sloping to very steep slopes at elevations of 25 to 3,500 feet. The climate is subhumid mesothermal with warm dry summers and cool moist winters. Mean annual precipitation is 12 to 25 inches. Average January temperature is about 48 degrees F., average July temperature is about 69 degrees F., and the mean annual temperature is about 58 degrees to 62 degrees F. The average freeze-free season is 240 to 300 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Altamont, Castaic, and Nacimiento soils and the Diablo, Huerhuero, San Ysidro, and Soper soils. Diablo soils are clays with a chroma of less than 1.5 in the upper part. Huerhuero, San Ysidro, and Soper soils have argillic horizons and Huerhuero and San Ysidro soils have ochric epipedons.

DRAINAGE AND PERMEABILITY: Well-drained; medium to very rapid runoff; moderately slow permeability.

USE AND VEGETATION: Used primarily for range. Some areas are used for growing cultivated crops. Vegetation is mostly annual grass and forbs with some scattered oak and patches of brush.

DISTRIBUTION AND EXTENT: Central and southern part of the Coast Range in California. The soils are extensive.


SERIES ESTABLISHED: San Benito County, California, 1971.

REMARKS: San Benito series was formerly classified as a regosolic member of the Chestnut group.

The activity class was added to the classification in February of 2003. Competing series were not checked at that time. - ET

OSED scanned by SSQA. Last revised by state on 11/72.

National Cooperative Soil Survey