LOCATION SOBEGA CAEstablished Series
TAXONOMIC CLASS: Fine-loamy, mixed, active, mesic Humic Dystrudepts
TYPICAL PEDON: Sobega loam, on a southeast facing convex slope of 12 percent under ryegrass plantain, needlegrass, filaree, and soft chess at 80 feet elevation. (Colors are for dry soil unless otherwise stated. When described (1/20/75) the soil was moist throughout.)
A11--0 to 10 inches; brown (10YR 5/3) loam, very dark grayish brown (10YR 3/2) moist; moderate medium granular structure; slightly hard, very friable, slightly sticky and slightly plastic; common very fine and fine roots; many very fine and fine, and medium irregular and tubular pores; strongly acid (pH 5.5); clear wavy boundary. (6 to 10 inches thick)
A12--10 to 17 inches; brown (10YR 5/3) mixed with pale brown (10YR 6/3) loam, very dark grayish brown (10YR 3/2) mixed with dark yellowish brown (10YR 4/4) moist; weak medium subangular blocky structure; slightly hard, very friable, slightly sticky and slightly plastic; common very fine and fine roots; many very fine and fine irregular and tubular pores; medium acid (pH 5.8); clear wavy boundary. (7 to 15 inches thick)
B2t--17 to 22 inches; variegated yellow (10YR 7/6) and very pale brown (10YR 8/4) loam, variegated yellowish brown (10YR 5/4) and dark brown (10YR 3/3) moist; weak medium granular structure; hard, very friable, slightly sticky and slightly plastic; few very fine and fine irregular pores; few thin clay films in bridges between mineral grains; medium acid (pH 5.8); gradual irregular boundary. (5 to 10 inches thick)
Cr--22 to 38 inches; yellow and very pale brown (10YR 8/6, 8/4) soft, deeply weathered sandstone; medium acid (pH 5.8); thick clay films in fractures.
TYPE LOCATION: Marin County, California; near Tomales High School; about 400 feet east on road from field house and 100 feet south of road and about 1,800 feet east of Hwy 1 and 1,500 feet north of Tomales-Petaluma Road.
RANGE IN CHARACTERISTICS: Depth to a paralithic contact is 20 to 40 inches. Mean annual soil temperature is 55 degrees to 59 degrees F. The soil moisture control section is moist in some part from October until sometime in August. Moisture in the summer is due, in part, from heavy fog and low evapotranspiration rates. It is dry in all parts less than 45 consecutive days in August and September. Base saturation is less than 50 percent throughout the solum but commonly increases slightly with increasing depth. Organic matter is 1 percent or more to a depth of less than 20 inches. Reaction is very strongly acid to medium acid commonly becoming less acid with increasing depth. Gravel ranges from 5 to 15 percent. Clay averages 18 to 27 percent in the particle-size control section and there is only 1 or 2 percent more clay in the B horizon than the A horizon. The soil is loam or sandy loam.
The A horizon has dry color of 10YR 5/2 or 5/3 in the upper part and 10YR 5/3, 6/2, 6/3 or 6/4 in the lower part. Moist colors are 10YR 3/2 or 3/3 in the upper part and 10YR 3/2, 4/2, 4/3, 4/4, 5/2 or 5/3 in the lower part. This horizon has moderate granular or moderate subangular blocky structure.
The B2 horizon has dry color of 10YR 6/6, 6/8, 8/3, 8/4, 7/6 or 8/6 and moist color of 10YR 5/6, 5/8, 7/3, 7/4, 6/6, 7/6, 5/4, 3/3, 4/3, 4/4, 4/6 or 6/3. It has weak granular to moderate subangular blocky structure.
COMPETING SERIES: These are the Kehoe and Sirdrak series in other families. Kehoe and Sirdrak soils have isomesic soil temperature.
GEOGRAPHIC SETTING: Sobega soils are on uplands. Slopes are 2 to 50 percent. The soils formed in material weathered from coarse grained strongly weathered sandstone. Elevations are 50 to 800 feet. The climate is subhumid mesothermal with cool foggy summers and cool moist winters. Mean annual precipitation is 28 to 40 inches. Mean January temperature is about 44 degrees F.; mean July temperature is about 65 degrees F.; mean annual temperature is about 55 degrees to 59 degrees F. Frost-free season is about 275 to 300 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Olompali, Steinbeck, and Tomales soils. All of these soils have an argillic horizon.
DRAINAGE AND PERMEABILITY: Well drained; medium runoff; moderate permeability.
USE AND VEGETATION: Used mainly for range. Natural vegetation is annual grasses and forbs.
DISTRIBUTION AND EXTENT: Central coastal California. The series is of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Marin County, California, 1979.