LOCATION OLOMPALI CAEstablished Series
TAXONOMIC CLASS: Fine, smectitic, mesic Ultic Palexeralfs
TYPICAL PEDON: Olompali loam, on a southwest facing convex slope of 9 percent under annual grasses, wire grass, coyote brush, plantain and wildiris at 75 feet elevation. (Colors are for dry soil unless otherwise stated. When described (1/23/75) this soil was moist throughout.)
A11--0 to 8 inches; grayish brown (10YR 5/2) loam structure, very dark brown (10YR 2/2) moist; moderate fine subangular blocky parting to moderate coarse granular; slightly hard, friable, sticky and plastic; many very fine and fine roots; many very fine and fine interstitial and vesicular pores, common very fine tubular pores; medium acid (pH 6.0); clear wavy boundary. (4 to 9 inches thick)
A12--8 to 13 inches; variegated pale brown and grayish brown (10YR 5/2, 6/3) heavy loam, variegated very dark grayish brown and dark brown (10YR 3/2, 4/3) moist; moderate fine subangular blocky structure parting to weak medium granular; slightly hard, very friable, sticky and plastic; many very fine and fine roots; many very fine and fine interstitial and vesicular pores, common very fine tubular pores; slightly acid (pH 6.3); abrupt wavy boundary. (4 to 6 inches thick)
B21t--13 to 19 inches; yellowish brown (10YR 5/6) clay, yellowish brown (10YR 5/4) moist, large distinct light yellowish brown (10YR 6/4) mottles, strong brown (7.5YR 5/8) moist; moderate medium prismatic structure; hard, very firm, very sticky and very plastic; common very fine roots; few very fine interstitial pores; many moderately thick clay films in pores; neutral (pH 6.8); abrupt wavy boundary. (3 to 7 inches thick)
B22t--19 to 28 inches; variegated brown and yellowish brown (10YR 5/3, 5/4) clay, light olive brown (2.5Y 5/4) moist, many medium prominent yellowish brown (10YR 5/8) mottles, yellowish brown (7.5YR 5/8) moist; moderate medium subangular blocky structure; hard, very firm, sticky and plastic; few very fine roots; common very fine interstitial pores; many moderately thick clay films in pores; many large irregularly shaped manganese concretions; neutral (pH 7.0); gradual wavy boundary. (7 to 10 inches thick)
B23t--28 to 42 inches; mixed colors of pale brown, light yellowish brown and brownish yellow (10YR 6/3, 6/4, 6/6) gravelly clay, light olive brown (2.5Y 5/4) moist with large prominent yellowish brown (10YR 5/8) mottles moist; weak fine and medium subangular blocky structure; hard, very firm, sticky and plastic; few very fine roots; common very fine interstitial pores; many moderately thick clay films lining pores; common medium irregularly shaped manganese concretions; neutral (pH 7.0); abrupt wavy boundary. (13 to 15 inches thick)
B24t--42 to 60 inches; mixed colors of pale brown, light yellowish brown, and brownish yellow (10YR 6/3, 6/4, 6/6) clay with many large prominent yellowish brown (10YR 5/6) mottles, light olive brown (2.5Y 5/4) moist with many large prominent strong brown (7.5YR 5/8) moist mottles; massive; hard, very firm, sticky and plastic; few very fine roots; few very fine interstitial pores; continuous thick clay films lining pores; common medium irregularly shaped manganese concretions; neutral (pH 7.0).
TYPE LOCATION: Marin County, California; about 3/4 miles north on Highway 1 from entrance to Herb Angress Ranch, 100 feet SW of Highway 1, 122 degrees 51 feet 20 inches W. latitude and 38 degrees 10 feet 20 inches N. longitude.
RANGE IN CHARACTERISTICS: The solum is 60 inches or more thick. The mean annual soil temperature is 54 degrees to 59 degrees F. These soils are moist in all parts of the moisture control section from November through June. It is dry in some parts the rest of the time. Organic matter is more than 1 percent to a depth of 20 inches. Base saturation is 35 to 50 percent in some parts of the A horizon, and is 50 to 75 percent by sum of cations in all parts of the argillic horizon. Clay increase between the lower boundary of the A horizon and upper boundary of the Bt horizon is more than 15 percent absolute within 1 inch.
The A horizon has dry color of 10YR 4/2, 5/2, 5/3 or 6/3 and moist color of 10YR 2/2, 3/2 or 4/3. It is loam, silty loam, or clay loam. It is slightly acid or medium acid.
The Bt horizon has variegated dry color of 10YR 5/2, 5/3, 5/4, 5/6, 6/3, 6/4 or 6/6 and moist color of 10YR 4/3, 5/4, 5/8 or 2.5Y 5/4. It is medium acid to neutral and is clay or gravelly clay.
COMPETING SERIES: These are the Cotati, Cronkhite, Rohnerville and the Spreckles series in other families. Cotati soils have on a A2 horizon and strongly acid to extremely acid B2 horizon. Cronkhite soils have less than 15 percent clay increase between the lower part of the A horizon and upper part of the Bt horizon. Rohnerville soils have base saturation less than 35 percent above the paralithic contact. Spreckles soils have sola 22 to 36 inches thick and are underlain by cemented Tuffareous sediments.
GEOGRAPHIC SETTING: Olompali soils are on dissected marine terraces near the coast line. Slopes are 2 to 50 percent. The soils formed in alluvium from mixed sources. Elevations are 50 to 800 feet. The climate is subhumid mesothermal with warm dry summers and moist cool winters. Mean annual precipitation is 35 to 45 inches. Mean January temperature is about 48 degrees F; mean July temperature is about 58 degrees F. and mean annual temperature is 53 degrees F. to 58 degrees F. Frost-free season is 250 to 300 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Los Osos, Soulajule, Tocaloma and Yorkville soils and the competing Cronkhite soils. Los Osos, Soulajule and Tocaloma soils are 20 to 40 inches deep to a paralithic contact, and have a xeric soil moisture regime. Yorkville soils have a mollic epipedon.
DRAINAGE AND PERMEABILITY: Somewhat poorly drained; medium to rapid runoff; very slow permeability. This soil has a perched water table at a depth of 12 to 24 inches during the months of December to March on the clay B2t horizon. The water table is absent during the growing season.
USE AND VEGETATION: Used for rangeland, watershed and wildlife habitat. Vegetation is annual grasses and forbs and scattered shrubs.
DISTRIBUTION AND EXTENT: Cental and northern coastal California. The soils are of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Marin County, California, 1979.