Established Series


The Clear Lake series consists of very deep, poorly drained soils that formed in fine textured alluvium derived from mixed rock sources. Clear Lake soils are in flood basins, flood plains and in swales of drainageways. Slopes are 0 to 5 percent. The mean annual precipitation is about 20 inches and the mean annual air temperature is about 60 degrees F.

TAXONOMIC CLASS: Fine, smectitic, thermic Xeric Endoaquerts

TYPICAL PEDON: Clear Lake clay, annual pasture. (Colors are for dry soil unless otherwise stated when described there was a water table at 48 inches).

Ag--0 to 13 inches; dark gray (N 4/0) clay, very dark gray (N 3/0) moist, few fine faint redoximorphic concentrations; strong medium granular structure at the surface and strong very coarse prismatic structure below when dry, massive when wet; very hard, firm, very sticky and very plastic; many fine roots; common very fine and fine pores; grass seeds, grass and burned plant remains in cracks and along cleavage planes; neutral (pH 7.0); gradual wavy boundary. (4 to 15 inches thick)

Bssg1--13 to 19 inches; dark gray (N 4/0) clay, very dark gray (N 3/0) moist; strong coarse prismatic structure when dry, massive when wet; extremely hard, very firm, very sticky and very plastic; many fine roots; many very fine and fine pores; many slickensides; grass remains in cracks and along cleavage planes; moderately alkaline (pH 8.0); clear wavy boundary. (5 to 10 inches thick)

Bssg2--19 to 45 inches; dark gray (N 4/0) clay, very dark gray (N 3/0) moist; strong coarse prismatic structure; extremely hard, very firm, very sticky and very plastic; few roots; few very fine and fine pores; many slickensides; few fine iron-manganese concretions; smooth pressure faces on peds; slightly calcareous; moderately alkaline (pH 8.0); diffuse irregular boundary. (10 to 35 inches thick)

Bssk--45 to 60 inches; grayish brown (2.5Y 5/2) clay, light olive brown (2.5Y 5/4) moist; tongues of very dark grayish brown (2.5Y 3/2) moist in the upper part; light yellowish brown (10YR 6/4) masses of iron accumulations; massive; very hard, very firm, very sticky and very plastic; few fine roots; very few very fine pores; few slickensides; few fine iron-manganese concretions; few soft lime masses; slightly calcareous; moderately alkaline (pH 8.0).

TYPE LOCATION: Solano County, California; 300 feet south, 300 feet east of northwest corner of sec. 25, T. 6 N., R. 2 E.; 38 degrees, 20 minutes, 35 seconds north latitude and 121 degrees, 42 minutes, 41.7 seconds west longitude; NAD83

RANGE IN CHARACTERISTICS: The combined thickness of the Ag, Bssg, and Bssk horizons is more than 60 inches. The mean annual soil temperature is 59 degrees to 65 degrees F. On drying, large cracks extend as deep as 48 inches and form large prisms. The cracks open and close at least once each year and are open by June or July and are closed by October or November. Various amounts of undecomposed plant material and surface soil are in these cracks. Common to many slickensides are in the zone from 12 to 48 inches. In some pedons moderate amounts of plant remains are in the lower part of the Ag horizon and the upper part of the Bssg horizon as well as in tongues of the Ag horizon extending in to the Bssg horizon. These soils have a calcium to magnesium ratio of more than 2.

The Ag and Bssg horizons have 10YR, 2.5Y or 5Y hue or is of neutral hue; value ranges from 2 through 5. Chromas are 1 or 0 moist and dry. Moist values are 1 or 2 units darker. In some pedons, colors are mottled with hues of 7.5YR or 10YR, values of 3 to 5 and chromas of 2 to 6. In other pedons concretions of Fe and Mn are present. These horizons range from moderately acid to moderately alkaline (pH 5.6 to 8.4) in the upper part and from slightly alkaline to moderately alkaline and calcareous in the lower part. The more acid surfaces are probably the result of cultural practices, especially extensive use of fertilizers and other agricultural chemicals. In areas adjacent to streams or sloughs, there is an overwash of stratified fine sandy loam or silty clay loam. Texture is clay loam, silty clay or clay.

The Bssk horizon has 10YR, 2.5Y or 5Y hue or is neutral; value ranges from 3 through 6 and chroma from 1 through 6; colors are mottled with hues of 10YR, 7.5YR, 2.5Y and 5Y. This horizon ranges from slightly alkaline to strongly alkaline and is usually calcareous with segregations of accumulated lime in soft masses or seams. In some pedons the lower part is stratified and noncalcareous. Texture is silty clay or clay.

COMPETING SERIES: These are the Carhart, Copus, Dodgeland, and Hildreth series. Carhart soils are 20 to 40 inches to paralithic material. Hildreth soils overlie unrelated material and are somewhat poorly drained. Copus soils have neutral pH. Dodgeland soils have hue of 10YR and less than 40 percent clay in some horizons.

GEOGRAPHIC SETTING: Clear Lake soils are in flood basins, flood plains and in swales of drainageways. Slopes are 0 to 5 percent. Elevations are 5 to 2,000 feet. The soils formed in fine textured alluvium derived from igneous, metamorphic and sedimentary rocks. The soils are in a dry subhumid climate of relatively hot dry summers and cool moist winters. Mean annual precipitation ranges from 10 to 35 inches. Mean January temperature varies from 42 degrees to 47 degrees F., mean July temperature varies from 69 degrees to 72 degrees F., and mean annual temperature varies from 58 degrees to 62 degrees F. The frost-free season is 160 to 300 days. Cooler temperatures and a shorter frost-free season occurs in Lake County.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Cropley, Antioch, Capay, Pacheco, Salinas and San Ysidro soils. Antioch soils have natric horizons. Capay soils have a chroma of 2 or more throughout. Cropley soils have chromas of 1.5 or more within 40 inches. Pacheco and Salinas soils have a mollic epipedon and have less than 35 percent clay. San Ysidro soils have an ochric epipedon and lack cracks and slickensides.

DRAINAGE AND PERMEABILITY: Poorly drained; negligible to high runoff (if assumed concave runoff is always negligible); slow to very slow permeability. A water table is at depths of 4 to 10 feet in the late summer and in some areas is very near the surface during wet months of winter. Some areas are artificially drained.

USE AND VEGETATION: Used for growing many row crops such as tomatoes, beans and sugar beets, dry farmed to grain, or irrigated and dry farmed pasture. Also used for rangeland. Native vegetation is grasses and forbs.

DISTRIBUTION AND EXTENT: In central California coastal valleys, small valleys of the Coast Range and in the San Joaquin and Sacramento Valleys. The soils are moderately extensive in MLRA- 14, 15 and 17.


SERIES ESTABLISHED: Lake County (Clear Lake Area), California, 1927.

REMARKS: Hildreth soils are currently listed in the same family. As currently described, Hildreth soils would not classify as Vertisols. A part of the Hildreth soils may belong to another series or different subgroup. More study of the Hildreth soils is needed to accurately classify these soils. In future MLRA updates Clear Lake mapped in MLRA 17 should be separated from acreage mapped in MLRA 14 (Coast Range Valleys). Differentia in this family is weak and has overlapping colors, plus marginal separations based on reaction classes, salinity and other factors.

Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - 0 to 45 inches
Slickensides - 19 to 60 inches
Reduced matrix - 0 to 45 inches
Redox concentrations - 0 to 13 inches and 19 to 60 inches
Secondary carbonates - 45 to 60 inches
Aquic conditions - 0 to 60 inches

Series classification updated May 1996. Competing series not reviewed at that time.

ADDITIONAL DATA: Two pedons in Sonoma County, CA: S61CA-097-009 (40A-3087), at 38 degrees north latitude, 14 minutes, 54 seconds, 122 degrees West longitude, 36 minutes, 31 seconds; and S61CA-097-010 (40A-3088), at 38 degrees North latitude, 16 minutes, 14 seconds, 122 West longitude, 38 minutes, 38 seconds. Two pedons in Solano County: NSSL pedon S79CA-095-000-000 (type location) and S91CA-099-005 (partial pedon). One pedon in Colusa County: S89CA-011-005.

Runoff terminology adjusted 5/96 to the adjective criteria of the Soil Survey Manual, 10/93.
Edits made for SDJR projects 12/2014 - AEC

National Cooperative Soil Survey