LOCATION COLUSA             CA
Established Series
Rev: GMK/WFA/WBS/WRR
01/2001

COLUSA SERIES


The Colusa series consists of very deep, somewhat poorly drained soils that formed in alluvium from mixed sources. They are on nearly level flood plains with slopes of 0 to 2 percent. The mean annual precipitation is 16 inches and the mean annual temperature is about 61 degrees F.

TAXONOMIC CLASS: Coarse-loamy, mixed, superactive, thermic Typic Natrixeralfs

TYPICAL PEDON: Colusa loam - on a west facing slope of 2 percent in a pasture at an elevation of 50 feet. (Colors are for dry soil unless otherwise stated.)

A--0 to 2 inches; pale brown (10YR 6/3) loam, dark brown (10YR 3/3) moist; strong medium platy structure; very hard, friable, slightly sticky and slightly plastic; many coarse roots; common very fine tubular pores; very strongly alkaline (pH 9.3); clear smooth boundary.

Btn1--2 to 9 inches; pale brown (10YR 6/3) loam, dark brown (10YR 3/3) moist; strong fine prismatic parting to strong fine angular blocky structure; very hard, firm, slightly sticky and slightly plastic; many coarse roots; few coarse and many very fine tubular pores; few thin clay films line pores; very strongly alkaline (pH 10.2); clear smooth boundary.

Btn2--9 to 20 inches; pale brown (10YR 6/3) loam; dark brown (10YR 3/3) moist; moderate coarse parting to weak moderater prismatic structure; hard, friable, slightly sticky and slightly plastic; common coarse roots; common coarse, many very fine and few fine and medium tubular pores; few thin clay films line pores; very strongly alkaline (pH 10.5); clear smooth boundary.

Btn3--20 to 26 inches; pale brown (10YR 6/3) loam, dark brown (10YR 3/3) moist; moderate medium angular blocky structure; hard, friable, slightly sticky and slightly plastic; few coarse roots, common very fine, fine and medium tubular pores; few thin clay films line pores and ped faces; very strongly alkaline (pH 10.5); clear smooth boundary.

Btn4--26 to 37 inches; pale brown (10YR 6/3) loam, dark brown (10YR 3/3) moist; moderate medium angular blocky structure; hard, friable, slightly sticky and slightly plastic; common coarse and many fine tubular pores; few thin clay films line pores and ped faces, many moderately thick clay films line planes of strata; very strongly alkaline (pH 10.6); abrupt smooth boundary.

Btn5--37 to 53 inches; pale brown (10YR 6/3) loam, brown (10YR 4/3) moist; moderate medium angular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine and few medium tubular pores; few thin clay films line pores and ped faces; very strongly alkaline (pH 10.5); clear smooth boundary.

Bn1--53 to 65 inches; brown (10YR 5/3) fine sandy loam, dark brown (10YR 4/3) moist; moderate medium angular blocky structure; slightly hard, friable, slightly sticky and slightly plastic, common very fine, fine and few medium tubular pores; very strongly alkaline (pH 10.3); clear smooth boundary.

Bn2--65 to 80 inches; brown (10YR 5/3) fine sandy loam, olive brown (2.5Y 4/3) moist; moderate medium angular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common fine, few very fine and medium tubular pores; very strongly alkaline (pH 10.0).

TYPE LOCATION: Colusa County, California; about 1 mile south of the town of Colusa CA; 1200 feet north and 2180 feet east of the southwest corner of Sec. 33, projected, T.16N,.R. 1W. MDB&M; 39 degrees, 11 minutes, 35 seconds North latitude and 121 degrees, 59 minutes, 40 seconds West longitude; USGS Meridian CA quadrangle.

RANGE IN CHARACTERISTICS: The mean annual soil temperature is 63 to 65 degrees F and the soil temperature is not below 47 degrees F at any time. The soil between the depths of 6 and 18 inches is dry in all parts from May 15 to October 31 and moist in some part from November 1 to May 15. Weighted average clay content of the 2 to 22 inch textural control section ranges from 14 to 18 percent clay. Depth to natric horizon ranges from 0 to 10 inches.

The A horizon is 10YR 6/3, 6/2, 5/2 and 10YR 4/2, 3/3, 3/2 moist. Texture is loam. Reaction is slightly alkaline to very strongly alkaline. SAR ranges from 50 to 100.

The Btn horizon is 10YR 6/3, 5/3, 4/3. Moist colors are 10YR 3/2, 3/3. Texture is loam or silt loam. Reaction is strongly alkaline or very strongly alkaline. SAR ranges from 75 to 175.

The Bn horizon is 2.5Y 6/4, 6/2; 10YR 6/3, 6/4, 5/3. Moist colors are 2.5Y 5/4, 5/2, 4/3. Texture is fine sandy loam or loam. Reaction is strongly to very strongly alkaline. SAR ranges from 15 to 75.

COMPETING SERIES: There are no other series in this family. Solano and Waukena soils in other families average greater than 18 percent clay in the textureal control section. Solano has strongly acid A horizons and Waukena has calcareous Bt horizons.

GEOGRAPHIC SETTING: Colusa soils are on nearly level high flood plains at elevations of 35 to 60 feet. The soils formed in mixed alluvium. The climate has hot dry summers and cool moist winters with frequent fogs. Mean annual precipitation varies from 14 to 16 inches. Average January temperature is about 45 degrees F; average July temperature is about 78 degrees F.Mean annual temerature is 60-62 degrees F. The frost-free season is 225 to 250 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are Vina and Moonbend soils. Vina soils lack sodium in the profile. Moonbend soils have fine-silty textural control sections and lack sodium in the profile.

DRAINAGE AND PERMEABILITY: Somewhat poorly drained, negligible to low runoff; slow permeability, some improvement of drainage has occured due to levee and flood control structures on the Sacramento River. Water tables fluctuate with water levels in adjacent streams. A fluctuating water table occurs below 40 inches during the months of December thru March.

USE AND VEGETATION: Pasture, both dryland and irrigated saltgrass. Small areas are occasionally cropped with poor results. Natural vegetation is salt grass and other halophytic plants. Scattered valley oaks and cottonwoods are found along channels.

DISTRIBUTION AND EXTENT: Flood plain of the Sacramento River in the lower Sacramento Valley. The soils are not extensive. MLRA 17.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California

SERIES ESTABLISHED: Colusa County, Soil Survey Area, 1997. Series was originally proposed in 1944, Colusa County, CA.

REMARKS: The series had been used in MLRA 30 as recorded in SC file (found in MUIR database). This needs to de corrected during updates.

Major Diaognostic Horizons:

1. Ochric Epipedon - 0 to 2 inches (A) ranges from 2 to 11 inches thick.

1.1 SAR > 15.

2. Natric horizon - 2 to 80 inches (Btn1, Btn2, Btn3, Btn4, Btn5) ranges from 11 to 54 inches thick.

2.1 Clay increase is more than 1.2 times A horizon.

2.2 Clay films line pores.

2.3 SAR exceeds 15 in all parts.

Other Diagnostic Horizons or Soil Characteristics:

1. Bn horizon - 53 to 80 inches (Bn1, Bn2)

1.1 SAR is > than 15.

2. EC is less than 12 throughout profile.

ADDITIONAL DATA: NSSL sample # S89CA-011-001 (89P-62).


National Cooperative Soil Survey
U.S.A.