LOCATION POMO CAEstablished Series
TAXONOMIC CLASS: Fine-loamy, mixed, superactive, thermic Typic Haploxeralfs
TYPICAL PEDON: Pomo loam - on a southeast facing slope of 20 percent under annual grasses and forbs at 2,120 feet elevation. (Colors are for dry soil unless otherwise stated. When described October 27, 1978, the soil was dry throughout.)
A1--0 to 1 inch; yellowish brown (10YR 5/4) loam, dark brown (10YR 3/3) moist; moderate medium granular structure; soft, very friable, slightly sticky and nonplastic; many very fine and fine roots; many fine and medium interstitial pores; 3 percent pebbles 2 to 25 mm in diameter; neutral (pH 6.9); abrupt wavy boundary. (0 to 2 inches thick)
A2--1 to 11 inches; yellowish brown (10YR 5/4) loam, dark yellowish brown (10YR 4/4) moist; moderate medium coarse and very coarse prismatic structure, parting to coarse and very coarse angular blocky; slightly hard, very friable, slightly sticky and slightly plastic; many very fine roots; many very fine and fine, common medium and few coarse tubular pores; 7 percent pebbles 2 to 50 mm in diameter; neutral (pH 6.8); abrupt wavy boundary. (10 to 15 inches thick)
BA--11 to 20 inches; yellowish brown (10YR 5/4) gravelly loam, dark yellowish brown (10YR 3/4) moist; moderate fine medium and coarse subangular blocky structure; slightly hard, very friable, slightly sticky and slightly plastic; many very fine roots; many very fine and fine tubular and common medium tubular and interstitial pores; 15 percent pebbles 2 to 75 mm in diameter; neutral (pH 6.7); clear wavy boundary. (0 to 10 inches thick)
Bt1--20 to 28 inches; dark yellowish brown (10YR 4/4) gravelly loam, dark yellowish brown (10YR 3/4) moist; weak fine and medium subangular blocky structure; slightly hard, very friable, slightly sticky and slightly plastic; few very fine roots; many very fine and few fine and medium tubular and common fine interstitial pores; few thin clay films on peds and in pores; 15 percent pebbles 2 to 75 mm in diameter and 5 percent cobbles 8 to 15 cm in diameter; neutral (pH 6.7); gradual wavy boundary. (8 to 10 inches thick)
Bt2--28 to 40 inches; dark yellowish brown (10YR 3/4) gravelly loam, dark yellowish brown (10YR 3/6) moist; weak fine and medium subangular blocky structure; slightly hard, very friable, slightly sticky and slightly plastic; few very f1ne roots; many very fine and few medium and coarse tubular and many very fine and fine interstitial pores; few thin clay films on peds and in pores; 15 percent pebbles 2 to 75 mm in diameter and 5 percent cobbles 8 to 15 cm in diameter; neutral (pH 6.8); gradual wavy boundary. (9 to 12 inches thick)
C--40 to 58 inches; dark yellowish brown (10YR 3/4) very gravelly clay loam, dark yellowish brown (10YR 3/6) moist; massive; hard, friable, sticky and slightly plastic; few very fine roots; many very fine tubular and interstitial pores; common thin clay films on rock fragments; 50 percent pebbles 2 to 75 mm in diameter; neutral (pH 6.8). (10 to 20 inches thick)
2R--58 inches; weathered fractured sandstone. Fractures occur at 3 to 10 inch intervals both horizontally and vertically and are 0 to 1 inch wide.
TYPE LOCATION: Lake County, California; about 875 feet east and 1,370 feet south of the northwest corner of sec. 28, T. 16 N., R. 10 W.
RANGE IN CHARACTERISTICS: The depth of a lithic contact typically is 50 to 60 inches but ranges from 40 to 60 inches. The solum ranges from 21 to 42 inches thick. The soil profile has 0 to 5 percent coarse and very coarse sand. The soil between the depth of 7 and 21 inches is moist in all parts between January 1 to April 15. It is dry in all parts from 75 to 90 days from June 15 to September 15. The mean annual soil temperature is 59 degrees to 62 degrees F. Most pedons are neutral throughout but some range to moderately acid in the lower part of the profile.
The A horizon is 7.5YR 5/4; 10YR 5/3 or 5/4. Moist color is 7.5YR 4/4; 10YR 4/3 or 4/4. There is usually a thin (1 to 2 inch) surface layer with moist colors of 10YR 3/2 or 3/3. It is sandy loam or loam and gravel ranges from 1 to 15 percent. Some pedons lack a BA horizon.
The Bt horizon is 7.5YR or 10YR 4/4, 5/4 or 10YR 3/4. Moist color is 7.5YR or 10YR 3/4, 3/6, 4/4 or 5/4 moist. It is gravelly loam or gravelly clay loam and has 15 to 35 percent gravel and 2 to 10 percent cobbles. Base saturation is 75 to 90 percent (sum of cations). Few thin to common moderately thick clay films are on peds and in pores. The absolute clay increase from the A to Bt horizon is 3 to 7 percent. Clay content varies from 25 to 35 percent.
The C horizon is gravelly clay or very gravelly clay loam and has 30 to 50 percent clay. Gravel content ranges from 20 to 60 percent.
COMPETING SERIES: These are the Arbuckle, Blasingame, Borden, Bressa, Fallbrook, Montpellier, Sesame, Snelling, Tivy (T), Wasioja and Wyman series. Arbuckle soils formed in alluvium, are dry in all parts from 145 days and have a massive and hard surface horizon. Blasingame, Bressa, Sesame and Tivy soils have a paralithic contact at 20 to 40 inches. Borden and Wasioja soils are calcareous in the lower Bt horizon and in the C horizon. Fallbrook soils have 15 to 28 percent coarse and very coarse sand. Montpellier soils have more than 15 percent coarse and very coarse sand and have hues of 5YR or 2.5YR in the argillic horizons. Wyman soils have massive and hard A1 horizons and 7.5YR and 5YR hues in the B2t horizon. Snelling soils have more than 20 percent coarse and very coarse sand and are dry in the moisture control section for more than 200 days.
GEOGRAPHIC SETTING: Pomo soils are on hills and mountains. They usually occur on south, southeast or southwest facing slopes. Slopes are 15 to 50 percent and are complex because of high frequency of landslips occurring on this soil. Pomo soils formed in colluvium or material weathered from sandstone, shale, and graywacke. Elevations are 1,400 to 3,000 feet. The climate is subhumid with hot dry summers and cool wet winters. Mean annual precipitation is 30 to 40 inches. Mean January temperature is 40 degrees F; mean July temperature is 70 degrees F; mean annual temperature is 56 degrees to 59 degrees F. Frost-free season is 155 to 200 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Bressa soils and the Maymen, Millsholm, and Sleeper soils. Maymen and Millsholm soils are less than 20 inches to a lithic contact. Sleeper soils are fine.
DRAINAGE AND PERMEABILITY: Well drained; rapid to very rapid runoff; moderately slow permeability.
USE AND VEGETATION: Used mostly for rangeland. Vegetation is annual grasses and some forbs consisting mainly of soft chess, purple needlegrass and filaree.
DISTRIBUTION AND EXTENT: Foothills and lower mountains in the Coast Range of northern California. These soils are not extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Lake County, California 1983.
REMARKS: The activity class was added to the classification in January of 2003. Competing series were not checked at that time. - ET
OSED scanned by SSQA. Last revised by state on 3/84.