Established Series


The Vallecitos series consists of shallow, well drained soils formed from metamorphic bedrock. Vallecitos soils are on hills and have slopes of 9 to 75 percent. The mean annual precipitation is about 18 inches and the mean annual temperature is about 60 degrees F.

TAXONOMIC CLASS: Clayey, smectitic, thermic Lithic Ruptic-Inceptic Haploxeralfs

TYPICAL PEDON: Vallecitos gravelly loam - rangeland. (Colors are for dry soil unless otherwise noted.)

A1--0 to 1.5 inches; brown (10YR 5/3) gravelly loam, dark brown (10YR 3/3) moist; weak fine granular structure; soft, friable; slightly sticky and slightly plastic; many very fine roots; many very fine pores; moderately acid (pH 6.0); clear smooth boundary. (1 to 3 inches thick)

A2--1.5 to 6 inches; brown (7.5YR 5/3) gravelly loam, dark brown (7.5YR 3/3) moist; massive; hard, friable, slightly sticky and plastic; many very fine roots; many very fine pores; slightly acid (pH 6.5); abrupt wavy boundary. (3 to 9 inches thick)

Bt1--6 to 12 inches; reddish brown (5YR 4/3) clay loam, dark reddish brown (5YR 3/3) moist; weak angular blocky structure; very hard, firm, slightly sticky and very plastic; common very fine roots; many very fine pores; thin continuous clay films lining pores and as bridges; neutral (pH 7.0); clear smooth boundary. (0 to 12 inches thick)

Bt2--12 to 16 inches; brown (10YR 4/3) clay loam, brown (10YR 4/3) moist; massive; very hard, firm, slightly sticky and very plastic; few very fine roots; common very fine pores; thin continuous clay films lining pores and as bridges; neutral (pH 7.0); abrupt broken boundary. (0 to 8 inches thick)

R--16 to 20 inches; bluish gray (5B 5/1) metamorphosed bedrock with clay films along cleavage planes.

TYPE LOCATION: Alameda County, California; 0.5 miles north and .1 mile east of the NW corner, sec. 9; NW1/4, SE1/4 NW1/4 section 9, T.5 S., R.4 E.

RANGE IN CHARACTERISTICS: Depth to a lithic contact is 10 to 20 inches (See Remarks). Depth to bedrock varies sharply over a surface distance of 20 to 80 inches. Usually the soil below a depth of 5 inches is continuously moist in some or all parts from November until April or May. The soil is dry all the rest of the year. The mean annual soil temperature is about 61 to 67 degrees F. The soil is neutral to moderately acid throughout and the pH is not below 6.0. It does not become more acid with depth. Dominantly rock fragments are less than 1 1/2 inches in diameter and make up less than 30 percent of the profile.

The A horizon is 10YR 6/3, 5/2, 5/3, 5/4; 7.5YR 6/2, 5/2, 5/3, 5/4. Moist colors are 10YR 4/3, 4/2, 3/3, or 7.5YR 4/2, 3/3, 3/2. It is loam, fine sandy loam or gravelly loam and in most pedons is massive and hard in some or all parts. Organic matter is about 1.2 to 2 percent in most parts and is as much as 4 to 5 percent in the uppermost few inches. The lower boundary is abrupt to clear. It has 20 to 27 percent clay and 0 to 25 percent gravel.

The Bt horizon is 10YR 6/3, 6/2, 4/3; 7.5YR 4/4, 5/4, 5/6, 6/2, 6/4 or more commonly reddish brown 5YR 4/3, 4/6, 5/3, 5/4, 5/6, 6/3, 6/4. Moist color is 10YR 4/3, 4/2, 3/3; 7.5YR 4/4, 4/2; 5YR 4/4, 4/3 or 3/3. It is clay loam, clay, gravelly clay loam or gravelly clay. This horizon is massive or it has weak to moderate angular or subangular blocky structure. In some areas the Bt horizon is lacking. It has 35 to 50 percent clay and 0 to 30 percent gravel.

Some pedons have a clay loam BA horizon and it has the same range in color as the Bt horizon. In areas where a pedon is lacking a Bt horizon, an associated BA horizon, or a Bw horizon 2 to 7 inches thick is present. It is brown or reddish brown in 7.5YR or 5YR hue and has one or two units higher chroma or a redder hue or both than the A horizon. It is heavy loam or clay loam, but the difference in clay content between the A horizon and the Bw horizon is less than 20 percent. This horizon has few to common thin clay films.

COMPETING SERIES: There are no other soils in this family.

GEOGRAPHIC SETTING: Vallecitos soils are on 9 to 75 percent slopes at elevations of 100 to 3,000 feet on north slopes and up to 3,800 feet on south-facing slopes. They formed in material weathered from metamorphosed sandstone and shale dominantly of the Franciscan Formation. The climate is dry subhumid mesothermal with cool moist winters and warm dry summers. The mean annual precipitation is 12 to 25 inches. Snow is rare and quickly melted. Mean annual temperature is 57 to 64 degrees F., average January temperature is 46 to 51 degrees F., and average July temperature is 70 to 77 degrees F. The frost-free period is 220 to 300 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Climara, Henneke, Lodo, Los Gatos and Montara soils and the competing Gaviota, Los Osos and Millsap soils. Climara soils have clay texture throughout and have intersecting slickensides. Henneke and Montara soils have mollic epipedons and serpentinitic mineralogy. Lodo soils have a mollic epipedon and lack an argillic horizon. Los Gatos soils are 24 to 40 inches deep to a lithic contact and have mesic temperature.

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

USE AND VEGETATION: Used mainly for livestock grazing. Vegetation is annual grasses, forbs and scattered oak, sagebrush, chamise and Digger pine.

DISTRIBUTION AND EXTENT: Coast Range of California, mostly in the central and north-central part. The series is extensive in MLRA-15.


SERIES ESTABLISHED: Alameda County (Livermore Valley Area), California, 1910.

REMARKS: The classification was updated in February 2001 using the Eighth Edition to Soil Taxonomy. This series was formerly classified as clayey, smectitic, thermic Lithic Ruptic-Xerochreptic Haploxeralfs. Competing series were not checked at that time.

Diagnostic horizons and features recognized in this pedon are:

Ochric epipedon - the zone from the surface to a depth of 6 inches (A1,A2)

Argillic horizon - the zone from 6 to 16 inches (Bt1, Bt2). This horizon is discontinuous.

Lithic contact - the boundary at 16 inches (R)

ADDITIONAL DATA: Laboratory data on the typifying pedon is S59Calif-01-8.

National Cooperative Soil Survey