LOCATION SWEEN CA
The Sween series consists of moderately deep, well drained soils that formed in material weathered from basic igneous rocks. Sween soils are on rounded hills and uplands and have slopes of 15 to 50 percent. The mean annual precipitation is about 17 inches and the mean annual air temperature is about 60 degrees F.
TAXONOMIC CLASS: Fine, smectitic, thermic Typic Argixerolls
TYPICAL PEDON: Sween clay loam, annual grass pasture. (Colors are for dry soil unless otherwise noted.)
A11--0 to 4 inches; gray (10YR 5/1) clay loam, very dark gray (10YR 3/1) moist; moderate fine granular structure; hard, friable, sticky and plastic; many very fine and fine root; common very fine and fine interstitial pores; moderately acid (pH 6.0); clear smooth boundary. (3 to 7 inches thick)
A12--4 to 13 inches; gray (10YR 5/1) clay loam, very dark gray (10YR 3/1) moist; weak medium subangular blocky structure; hard, friable, sticky and plastic; many very fine and fine roots; many very fine, common fine tubular pores; slightly acid (pH 6.2); clear smooth boundary. (7 to 12 inches thick)
B21t--13 to 19 inches; light brownish gray (2.5Y 6/2) clay, dark grayish brown (2.5Y 4/2) moist; strong medium angular blocky structure; very hard, very firm, very sticky and very plastic; common very fine and fine roots; common very fine and fine tubular pores; thin continuous clay films on faces of peds and lining pores; few fine and medium slickensides; neutral (pH 7.0); gradual smooth boundary. (4 to 8 inches thick)
B22t--19 to 27 inches; pale brown (10YR 6/3) clay, brown (10YR 4/3) moist; strong medium angular blocky structure; very hard, very firm, very sticky and very plastic; common very fine roots; common very fine tubular pores; thin continuous clay films on faces of peds; slightly alkaline (pH 7.5); gradual smooth boundary. (6 to 10 inches thick)
C--27 to 32 inches- light yellowish brown (10YR 6/4) coarse sandy loam, dark yellowish brown (10YR 4/4) moist; weak medium subangular blocky structure; very hard, very firm, sticky and plastic; few very fine roots; few very fine tubular pores; slightly alkaline; gradual irregular boundary. (0 to 12 inches thick)
R--32 to 40 inches; yellowish brown and gray partially weathered basic igneous rock.
TYPE LOCATION: San Benito County, California; 1/2 mile northeast of junction of U. S. Highway 101 and State 156 on U. S. 101, 100 yards northwest of highway.
RANGE IN CHARACTERISTICS: Depth to a lithic contact of basic igneous rock is 24 to 40 inches. The mean annual soil temperature is about 62 degrees to 64 degrees F. and the soil temperature usually is not below 47 degrees F. at any time. The soil between depths of about 5 and 15 inches is usually dry all of the time from May until about mid-December and is moist in some or all parts all the rest of the year. Cobblestones and gravel make up as much as 35 percent of the A and C horizons and up to 25 percent of the B2t horizons in some pedons. Other pedons have as little as 1 or 2 percent rock fragments in all horizons. Base saturation is more than 75 percent in all parts of the profile.
The A horizon is gray, dark gray or dark grayish brown (10YR 5/1, 4/1, 4/2; 2.5Y 4/2). It is loam or clay loam and is neutral to medium acid. The horizon has weak or moderate granular or subangular blocky structure. It has approximately 3 or 4 percent organic matter in the upper part and 1 to 1.5 percent in the lower part.
The B2t horizon is pale brown, light brownish gray, brown, yellowish brown, light yellowish brown or grayish brown (10YR 6/3, 6/2, 5/3, 5/4, 2.5Y, 6/2, 6/4, 5/2). It is heavy clay loam or clay and has 35 to 50 percent total clay. Absolute clay increase from the A horizon to the B2t horizon is 10 to 15 percent and the upper boundary of the B2t horizon is clear to gradual. This horizon has moderate to strong angular blocky or subangular blocky structure. It is slightly acid to mildly alkaline.
The C horizon is light yellowish brown, pale brown, yellowish brown or light olive brown (10YR 6/4, 6/3, 5/4; 2.5Y, 6/4, 5/4). It is coarse sandy loam, sandy loam to sandy clay loam or clay loam and is mildly or moderately alkaline, but is noncalcareous. The C horizon of soil material is thin or lacking in some pedons.
COMPETING SERIES: These are the Pagan,
Fagan and Todos soils are 40 to 60 inches deep to weathered sandstone and shale. Gabino and Sespe soils have B2t horizon hue of 5YR or 2.5YK. Los Osos soils have a paralithic contact at depths of 24 to 40 inches, and have an increase (absolute) of 6 to 10 percent clay from the A horizon to the B2t horizon.
GEOGRAPHIC SETTING: The Sween soils are on rounded hills and have slopes of 15 to 50 percent. Elevations are 0 to 2,500 feet. They formed in material weathered from basic igneous rock. The climate is dry subhumid mesothermal with warm dry summers and cool moist winters. Mean annual precipitation is 14 to 20 inches. Average January temperature is 49 degrees F., average July temperature is 68 degrees F., and mean annual temperature is 60 degrees F. The freeze-free season is 260 to 290 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing
Los Osos soils and the
San Benito soils. Cibo soils lack a B2t horizon and have more than 35 percent clay throughout the profile Henneke soils have serpentine bedrock at a depth of less than 20 inches. San Benito soils lack a B2t horizon and have less than 35 percent clay throughout the profile.
DRAINAGE AND PERMEABILITY: Well-drained; rapid to very rapid runoff; slow permeability.
USE AND VEGETATION: Used mainly for grazing. Vegetation is annual grasses and forbs with a few shrubs and a few scattered live oak trees.
DISTRIBUTION AND EXTENT: Central part of the Coast Range in California. The soils are inextensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: San Benito County, California 1973.
OSED scanned by SSQA. Last revised by state on 12/76.
National Cooperative Soil Survey