LOCATION LOS ROBLES CAEstablished Series
TAXONOMIC CLASS: Fine-loamy, mixed, superactive, thermic Typic Haploxerepts
TYPICAL PEDON: Los Robles clay loam - on a less than 1 percent slope in a cultivated area at 250 feet elevations. (Colors are for dry soil unless otherwise stated.)
Ap--0 to 7 inches; brown (10YR 4/3) clay loam, very dark brown (10YR 2/2) moist; cloddy; hard, firm, sticky and plastic; many very fine roots; many very fine and fine, few medium tubular and interstitial pores; neutral (pH 6.6); abrupt smooth boundary. (4 to 10 inches thick)
Bw--7 to 20 inches; brown (10YR 4/3) clay loam, very dark brown (10YR 2/2) moist; moderate medium subangular blocky structure; very hard, firm; sticky and plastic; many very fine, common fine, few medium roots; many very fine and fine, few medium tubular and interstitial pores; continuous thin clay films lining pores; neutral (6.6); gradual wavy boundary. (10 to 25 inches thick)
BC--20 to 44 inches; brown (10YR 4/3) clay loam, dark brown (10YR 3/3) moist; weak medium subangular blocky structure; hard, firm, sticky and plastic; common very fine, fine and medium roots; many very fine and fine tubular and interstitial pores; common thin clay films lining pores; neutral (pH 6.6); gradual wavy boundary. (20 to 30 inches thick)
C--44 to 60 inches; brown (10YR 5/3) clay loam, dark brown (10YR 3/3) moist; massive; hard, firm, sticky and plastic; few very fine, fine and medium roots; many very fine and fine, few medium tubular and interstitial pores; neutral (pH 6.6).
TYPE LOCATION: Tehama County, California; 660 feet west of HWY 99E on Oklahoma Avenue, just N of Dairyville; in T.26 N, R.2 W. Red Bluff quadrangle.
RANGE IN CHARACTERISTICS: The soil between the depths of 5 and 15 inches is moist in all parts from November 15 to May 15 and is dry in all parts from June 1 to October 15. The mean annual soil temperature is about 61 to 67 degrees F. and is never below 47 degrees F. at any time. Most pedons have less than 15 percent gravel in all horizons, usually less than 5 percent. Some pedons have 15 to 35 percent gravel throughout. Some pedons have 35 to 60 percent gravel in the lower C horizons. Some part of the 10 to 40 inch zone has 27 to 35 percent clay contents.
The A horizon is 10YR 5/3, 5/2, 4/2, 4/3, 3/2, 3/3; 7.5YR 3/2, 4/2, 5/2. Moist colors are 10YR 2/2, 3/2, 3/3, 4/2; 7.5YR 3/2. It is loam, silt loam or clay loam or their gravelly equivalents. In most pedons it is massive and hard or very hard in some or all parts. It has 1.5 to 3.5 percent organic matter in the upper half and averages less than 1 percent in the lower half. It is slightly acid or neutral.
The Bw horizon is 10YR 5/3, 4/3, 4/2; 7.5YR 4/2, 4/4, 5/4; 5YR 5/2, 5/3. Moist colors are 4/3, 3/3, 3/2, 2/2; 7.5YR 3/2, 3/4; 5YR 3/2, 3/3. It is heavy loam, heavy silt loam, clay loam or the gravelly equivalents. It has weak or moderate structure. There is less than 1.2 times as much clay increase compared to the A horizon. It is slightly acid to slightly alkaline.
The C horizons is less red or has lower chroma than the Bw horizon and is 2.5Y 4/2; 10YR 5/3, 4/3; 7.5YR 4/4; 5YR 5/4. Moist colors are 2.5Y 3/2; 10YR 4/3, 3/3; 7.5YR 3/4; 5YR 3/3. It is slightly acid to slightly alkaline and is a few pedons there is a small amount of segregated lime in the lower part. Some pedons have an indurated hardpan below 40 inches.
COMPETING SERIES: This is the Zacharias (T) series. It is more than 175 days dry in all parts, and in addition formed in alluvium from mixed sources and the rainfall is 8 to 12 inches.
GEOGRAPHIC SETTING: The Los Robles soils are on fans and terraces and have slopes of 0 to 15 percent. The soils formed in material from basalt and andesitic rocks. Elevations are 100 to 1,000 feet. The climate is subhumid with hot dry summers and cool moist winters. Mean annual precipitation varies from 13 to 35 inches. The mean January temperature is 47 to 52 degrees F.; the mean July temperature is 70 to 79 degrees F.; mean annual temperature varies from 58 to 65 degrees F. Frost free season is about 220 to 310 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Brentwood, Cropley, Keefers, Rincon, Tuscan and Zamora soils. Brentwood soils have a fine textural control section and typically are on nearly level fans. Cropley soils have a clay texture and intersecting slickensides and are on nearly level flood plains or gently to moderately sloping fans. Keefers soils have an argillic horizons, are skeletal and are on similar landscape. Rincon and Zamora soils both have argillic horizons with Rincon having a fine textural control section and Zamora having a fine-silty one. Tuscan soils have a duripan at a depth of less than 20 inches. Rincon, Tuscan and Zamora are on similar topography.
DRAINAGE AND PERMEABILITY: Well drained; slow to medium runoff; moderately slow permeability.
USE AND VEGETATION: Used for cropland with such crops as irrigated fruit and nuts, field crops, pasture and rangeland. Uncultivated areas have a cover of annual grasses and forbs and some have scattered valley oak or live oak.
DISTRIBUTION AND EXTENT: Dominantly edges and inter-mountain valleys near the Sacramento Valley, California.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California.
SERIES ESTABLISHED: Tehama County, California; l962.
REMARKS: Study of profile descriptions and limited data indicate that most of the Los Robles soils lack sufficient clay increase for an argillic horizon. Accordingly, the series is removed from the fine-loamy, mixed, thermic family of Mollic Haploxeralfs. Former Los Robles pedons that have an argillic horizon will mostly go to the Pleasanton series.
Series description entered into Ames database on 04/2000. The classification was updated in February 2001 using the Eighth Edition to Soil Taxonomy. This series was formerly classified as fine-loamy, mixed, thermic Typic Xerochrepts. Lab data was unavailable at that time to indicate whether minerology is isotic. Competing series were not checked at that time.
Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - 0 to 7 inches (Ap)
Cambic horizon - 7 to 20 inches (Bw)