LOCATION CORVAL CAEstablished Series
TAXONOMIC CLASS: Fine-silty, mixed, superactive, thermic Pachic Haploxerolls
TYPICAL PEDON: Corval loam - on a east facing slope of 1 percent under annual grasses at an elevation of 250 feet. (Colors are for dry soil unless otherwise stated.)
A--0 to 8 inches; brown (10YR 4/3) loam, very dark grayish brown (10YR 3/2) moist; moderate fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine roots; common very fine tubular pores; slightly acid (pH 6.2); abrupt smooth boundary. (8 to 25 inches thick)
Bw1--8 to 24 inches; brown (10YR 4/3) clay loam, dark brown (10YR 3/3) moist; moderate fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine roots; many very fine and few fine tubular pores; slightly acid (pH 6.3); clear smooth boundary.
Bw2--24 to 36 inches; brown (10YR 4/3) clay loam, dark brown (10YR 3/3) moist; moderate fine angular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; few very fine roots; many very fine tubular pores; slightly acid (pH 6.5); clear smooth boundary.
Bw3--36 to 46 inches; dark yellowish brown (10YR 4/4) clay loam, dark yellowish brown (10YR 3/4) moist; moderate fine angular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; few very fine roots; many fine tubular pores; neutral (pH 6.6); clear smooth boundary.
Bw4--46 to 60 inches; brown (10YR 4/3) clay loam, dark brown (10YR 3/3) moist; moderate fine angular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; few very fine roots; many very fine tubular pores; neutral (pH 6.6); clear smooth boundary.
Bw5--60 to 70 inches; dark yellowish brown (10YR 4/4) clay loam, dark yellowish brown (10YR 3/4) moist; moderate fine angular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine tubular pores; neutral (pH 6.8).
TYPE LOCATION: Colusa County, California; about 7.5 miles southwest of Williams CA; 2900 feet west and 1500 feet north of the southeast corner of Sec. 16, T.14N., R.3W.,MDB&M 39 degrees 3' 50" N. Latitude and 122 degrees 11' 50" W. longitude; USGS Cortina Creek CA quadrangel.
RANGE IN CHARACTERISTICS: The mean annual soil temperature is 59 to 63 degrees F. The soil between the depths of 6 and 17 inches is dry in all parts from May 15 to October 31 and moist in some or all parts from November 1 to May 15. Weighted average clay content of the 10 to 40 inch textural control section ranges from 27 to 35 percent clay.
The A horizon has dry color of 10YR 5/3, 4/3 and moist color of 10YR 3/3 or 3/2. Reaction is slightly acid. Texture is loam or clay loam.
The upper Bw horizon to a depth of at least 20 inches has dry color of 10YR4/3 and moist color of 10YR 3/3. Texture is silty clay loam or clay loam. Reaction is slightly acid to neutral.
The lower part of the Bw has dry color of 10YR 5/4,4/4,4/3 and moist color of 10YR 4/4,3/4 or 3/3. Texture is silty clay loam or clay loam. Reaction is slightly acid to neutral.
COMPETING SERIES: These are the Coyotecreek, Crow Hill, Horst, Moonbend and Suey series. Crow Hill soils have a paralithic contact at 20 to 40 inches and contain large amounts of diatomaceous earth. Coyotecreek and Horst soils average 18 to 27 percent clay in the textural control section. Moonbend soils are moderately well drained and stratified. Moonbend has temporary water tables, are effervescent and have greater than 40 percent silt. Suey soils formed in loess deposits on hills and terraces, average less than 27 percent clay in the textural control section and have a difference of 12 degrees F. between the mean winter and mean summer temperature.
GEOGRAPHIC SETTING: Corval soils are on nearly level high flood plains and alluvial fans at elevations of 90 to 1400 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 22 inches. Average January temperature is about 43 degrees F; average July temperature is about 76 degrees F. Mean annual temperature is 58 to 62 degrees F. The frost-free season is 185 to 250 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Capay, Goldeagle(T), Positas, Balcom and Westfan soils. Capay soils are in basins and have fine textures. Goldeagle(T) and Positas soils are on steep hills and have fine textured argillic horizons. Balcom soils are fine-loamy, have a paralithic contact at 20 to 40 inches and are on steep hills. Westfan soils are fine-loamy.
DRAINAGE AND PERMEABILITY: well drained; negligable to low runoff; moderately slow permeability. Subject to rare flooding.
USE AND VEGETATION: used for livestock grazing in upland valleys and for cropland in the Sacramento Valley. Native vegetation is scattered blue and valley oaks and annual grasses and forbs.
DISTRIBUTION AND EXTENT: High flood plains of streams in foothill valleys of the Coast Range west of the lower Sacramento Valley and alluvial fans in the lower Sacramento Valley. The soils are not extensive. MLRA 17 and some small areas of 15.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Colusa County SSA, California, Colusa
Soil Survey 1997. Source of name is coined from Cortina Valley.
DIAGNOSTIC Horizons and features recognized in this pedon are:
1. Mollic Epipedon - 0 to 36 inches (A,Bw1,Bw2) ranges
from 30 to 40 inches thick.
1.1 Organic carbon estimated to be greater than 0.70 percent.
1.2 Pachic Subgroup - Mollic epipedon extends to more than 20 inches.
2. Cambic horizon - 8 to 70 inches (Bw1,Bw2,Bw3,Bw4,Bw5)
ranges from 20 to more than 60 inches thick.
Other Diagnostic Horizons or Soil Characteristics:
1. Fine-silty family: Fine sand and coarser sands range
from 10 to 15 percent in the 10 to 40 inch textural control
section.
1.1 PSA by local hydrometer methods and #140 sieve analysis:
HORIZON DEPTH CLAY SILT SAND %FINE SAND+COARSER SANDS
A 0-8 26 36 38 13.4
Bw1 8-24 30 36 34 12.5
Bw2 24-36 32 38 30 14.4
Bw3 36-46 32 42 26 12.4
Bw4 46-60 32 32 36 18.6
Bw5 60-70 32 34 34 20.6
Weighted average clay content of the 10 to 40 inch textural
control section is 31.0 percent.
2. Temperature - Moisture (Xeric-Thermic)
2.1 The 6 to 17 inch SMCS is dry in all parts from May 15 to
October 31 and is moist in some or all parts from November 1
to May 15.
2.2 The MAST is 59 to 63 degrees F.