LOCATION BRESSA CAEstablished Series
TAXONOMIC CLASS: Fine-loamy, mixed, active, thermic Typic Haploxeralfs
TYPICAL PEDON: Bressa silt loam, annual grass rangeland. (Colors are for dry soil unless otherwise noted.)
A1--0 to 4 inches; pale brown (10YR 6/3) silt loam, brown (10YR 4/3) when moist; weak, medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine and fine roots; many very fine and fine tubular and interstitial pores; slightly acid (pH 6.5); clear, smooth boundary.
A2--4 to 10 inches; pale brown (10YR 6/3) silt loam, brown (10YR 4/3) when moist; weak, medium, subangular blocky structure; slightly hard, friable, sticky and plastic; many very fine and fine roots; many very fine and fine tubular and interstitial pores; slightly acid (pH 6.5); clear, smooth boundary. (Combined thickness of the A horizon is 6 to 12 inches).
BAt--10 to 15 inches; light yellowish brown (10YR 6/4) silty clay loam, dark yellowish brown (10YR 4/4) when moist; weak, medium, subangular blocky structure; hard, firm, sticky and plastic; common very fine and fine roots; many fine tubular and interstitial pores; few thin clay films on peds and in pores; slightly acid (pH 6.5); clear, smooth boundary. (3 to 6 inches thick)
Bt--15 to 23 inches; yellowish brown (10YR 5/4) silty clay loam, dark yellowish brown (10YR 4/4) when moist; moderate, medium, subangular blocky structure; hard, firm, sticky and plastic; common very fine, few coarse roots; many fine tubular and interestitial pores; many moderately thick clay films on peds and in pores, and as bridges; moderately acid (pH 5.6); gradual, smooth boundary. (5 to 10 inches thick)
Bct--23 to 33 inches; yellowish brown (10YR 5/4) silty clay loam, dark yellowish brown (10YR 4/4) when moist; moderate, medium, subangular blocky structure; hard, firm, sticky and plastic; few fine roots; many fine tubular and interstitial pores; many moderately thick clay films on peds in pores, and as bridges; moderately acid (pH 5.6); abrupt, smooth boundary. (6 to 12 inches thick)
Cr--33 to 37 inches; weathered soft, fractured fine grained sandstone.
TYPE LOCATION: Napa County, California; one mile north on Gordon Valley Road from intersection of Wooden Valley cross road; about 100 feet north on road from cattle guard and 150 feet east of road on hillside; NE 1/4 SW 1/4 sec 19, T. 6 N., R. 2 W. (Projected; in Spanish Land Grant).
RANGE IN CHARACTERISTICS: Depth to weathered sandstone or shale is 20 to 40 inches. The mean annual soil temperature is between 59 degrees and 69 degrees F, and the soil temperature is always above 41 degrees F. The soil between depths of about 6 and 17 inches is dry in all parts from June to October or November and is moist in all parts from December to April. Pebbles make up 2 to 15 percent. Coarse and very coarse sand make up less than 10 percent of the profile. The soil commonly increases in acidity as depth increases and is moderately acid to neutral.
The A horizon dry color is 10YR 7/1, 6/2, 6/3, 7/3 or 6/4. Moist colors are 10YR 3/2, 3/3, 3/4, 4/2, 4/3 or 4/4. In some pedons the top one or two inches is 10YR 5/2, 5/3. This horizon is silt loam, loam, fine sandy loam, or sandy loam. The pedons with silt loam are commonly underlain by shale, and the pedons with sandy loam are commonly underlain by sandstone. The surface 10 inches has 0.5 to 2.8 percent organic matter.
The Bt horizon dry color is 10YR 7/4, 6/4, 6/3, 5/4, 5/6; 2.5Y 4/4 or 7.5YR 6/6. Moist color are 10YR 4/2, 4/4, 5/4; 7.5YR 5/4 or 5/6. In some pedons, faces of peds are 10YR 7/3, 7/4, 8/3 or 8/2. This horizon is clay loam or silty clay loam, and has 27 to 35 percent clay. It has prismatic or subangular blocky structure. It has more than 75 percent base saturation.
The upper part of the weathered sandstone or shale commonly is moderately or slightly acid but within 30 inches in some pedons the reaction is slightly or moderately alkaline and is with or without seams of lime.
COMPETING SERIES: These are the Arbuckle, Blasingame, Borden, Esparto, Fallbrook, Montpellier, Pomo, Ramona, Sesame, Snelling, Tivy, Wasioja, and Wyman series. Arbuckle, Borden, Esparto, Montpellier, Pomo, Ramona, Snelling, Wasioja, and Wyman soils lack a paralithic contact within 40 inches of the surface. Blasingame soils have hue of 2.5YR or 5YR in the B2t horizon. Fallbrook soils have a paralithic contact at depth greater than 40 inches and have B2t horizons with 5YR hue. Sesame and Tivy soils have value of 4 or 5 in the A horizon and have 12 to 22 percent coarse and very coarse sand in the control section.
GEOGRAPHIC SETTING: Bressa soils have slopes of 5 to 75 percent and are at elevations of 400 to 3,000 feet. They formed in material weathered from fine grained sandstone and shale. The climate is subhumid with hot dry summers and cool moist winters. Mean annual precipitation is 20 to 40 inches. Mean January temperature is 47 degrees F.; mean July temperature varies from 72 to 75 degrees F.; and mean annual temperature is 55 to 68 degrees F. The frost free season is 150 to 290 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Contra Costa, Dibble, Fagan, Lodo, Maymen, Millsholm and Sobrante soils. Contra Costa, Dibble, and Fagan soils have fine control sections. Also, Fagan soils have mollic epipedons. Lodo, Maymen, and Millsholm soils have a lithic contact at depths of less than 20 inches. Sobrante soils have moist values of less than 3.5 in the upper A horizon and have 5YR and 2.5YR hues in the B2t horizon.
DRAINAGE AND PERMEABILITY: Well drained; medium to very rapid runoff; moderately slow permeability.
USE AND VEGETATION: Used for dryland range and as habitat for wildlife. Adjacent to lakes it is used for recreation. Vegetation is mainly annual grasses and forbs with a few scattered oak and Digger pines.
DISTRIBUTION AND EXTENT: Coast Ranges of Central California. The soils are moderately extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Napa County, California, 1974.
REMARKS: The activity class was added to the classification in January of 2003. Competing series were not checked at that time. - ET