The Willows series consists of very deep, poorly drained soils in basins. These soils formed in alluvium derived from mixed sources. Slope ranges from 0 to 2 percent. The mean annual precipitation is 14 to 16 inches, and the mean annual temperature is 60 to 62 degrees F.

Taxonomic class: Fine, smectitic, thermic Sodic Endoaquerts

Willows silty clay, 0 to 1 percent slopes, frequently flooded, in a fallow rice paddy. Described on September 24, 1993.

Ap1—0 to 5 inches; dark grayish brown (2.5Y 4/2) silty clay, very dark grayish brown (2.5Y 3/2) moist; weak medium subangular blocky structure parting to moderate medium coarse granular structure; very hard, firm, sticky and plastic; many very fine roots; many very fine and fine low continuity interstitial and tubular pores; noneffervescent; common fine distinct yellowish brown (10YR 5/4) cylindrical masses of iron accumulation; neutral (pH 7.0); clear smooth boundary.

Ap2—5 to 13 inches; dark grayish brown (2.5Y 4/2) silty clay, very dark grayish brown (2.5Y 3/2) moist; Weak coarse angular blocky structure; very hard, firm, sticky and plastic; common very fine roots; many very fine low continuity tubular pores; prisms 25 to 35 cm across; compacted layer; few prominent discontinuous pressure faces on faces of peds; noneffervescent; common fine distinct yellowish brown (10YR 5/4) masses of iron accumulation; moderately alkaline (pH 7.9); gradual smooth boundary.

Bw—13 to 20 inches; grayish brown (2.5Y 5/2) silty clay, very dark grayish brown (2.5Y 3/2) moist; moderate coarse angular blocky structure; very hard, firm, sticky and plastic; few very fine roots; many very fine low continuity tubular pores; prisms 25 to 35 cm across; compacted layer; few prominent discontinuous pressure faces on faces of peds; slightly effervescent on concretions; common fine irregular very dark gray (10YR 3/1) slightly hard iron-manganese concretions; few fine distinct yellowish brown (10YR 5/4) masses of iron accumulation; moderately alkaline (pH 8.1); gradual smooth boundary.

Bssy1—20 to 39 inches; brown (10YR 5/3) silty clay, brown (10YR 4/3) moist; strong coarse angular blocky structure; very hard, firm, sticky and plastic; few very fine roots; many very fine low continuity tubular pores; prisms 25 to 35 cm across, prisms break to wedge-shaped peds; few prominent discontinuous pressure faces on faces of peds and few prominent patchy organic coats in root channels and/or pores and common prominent continuous intersecting slickensides on faces of peds; common fine irregular white (10YR 8/1) soft masses of lime; common fine white threads white (10YR 8/1) soft masses of gypsum; common fine rounded very dark gray (10YR 3/1) slightly hard iron-manganese concretions; slightly alkaline (pH 7.8); clear smooth boundary.

Bssy2—39 to 54 inches; brown (10YR 5/3) silty clay, brown (10YR 4/3) moist; strong coarse angular blocky structure; very hard, firm, sticky and plastic; few very fine roots; many very fine low continuity tubular pores; prism break to wedge shaped peds, common prominent continuous intersecting slickensides on faces of peds; few prominent patchy organic coats in root channels and/or pores; common fine irregular white (10YR 8/1) soft masses of lime; common fine threads white (10YR 8/1) soft masses of gypsum; common fine rounded very dark gray (10YR 3/1) slightly hard iron-manganese concretions; strongly effervescent on concretions; moderately alkaline (pH 7.9); clear smooth boundary.

Bssy3—54 to 60 inches; brown (10YR 5/3) silty clay, brown (10YR 4/3) moist; moderate coarse angular blocky structure; very hard, firm, sticky and plastic; few very fine roots; many very fine low continuity tubular pores; prism break to wedge shaped peds; iron accumulations are along pore linings or on surfaces of slickensides; common prominent continuous intersecting slickensides on faces of peds; common fine irregular white (10YR 8/1) soft masses of lime; common fine threads white (10YR 8/1) soft masses of gypsum; common coarse and very coarse irregular soft masses of lime; common fine rounded iron-manganese concretions; strongly effervescent on concretions; few medium distinct light brownish gray (10YR 6/2) masses of iron accumulation, moderately alkaline (pH 8.0); gradual smooth boundary.

Bssy4—60 to 72 inches; brown (10YR 5/3) clay, brown (10YR 4/3) moist; common medium distinct gray (10YR 5/1) moist irregular iron depletions; moderate coarse angular blocky structure parting to moderate medium subangular blocky; very hard, firm, deformable, sticky and plastic; few very fine roots throughout; many very fine low continuity tubular pores; prisms break to wedge-shaped peds; iron depletions are along pore linings or on surfaces of slickensides; common prominent continuous intersecting slickensides on faces of peds; common fine irregular white (10YR 8/1) soft masses of lime throughout and common fine threads white (10YR 8/1) soft masses of gypsum throughout and common fine rounded slightly hard iron-manganese concretions throughout; strongly effervescent on concretions (HCL, 1 normal); moderately alkaline (pH 8.2); clear wavy boundary.

Bssy5—72 to 80 inches; yellowish brown (10YR 5/4) silty clay, dark yellowish brown (10YR 4/4) moist; common medium gray (10YR 5/1) moist irregular iron depletions; moderate coarse subangular blocky structure; very hard, firm, deformable, sticky and plastic; few very fine roots throughout; many very fine low continuity tubular pores; prisms break to wedge-shaped peds; iron depletions are along pore linings or on surfaces of slickensides; common prominent continuous intersecting slickensides on faces of peds; common fine irregular white (10YR 8/1) soft masses of lime throughout and common fine threads white (10YR 8/1) soft masses of gypsum throughout and common fine rounded very dark gray (10YR 3/1) slightly hard iron-manganese concretions throughout; strongly effervescent on concretions (HCL, 1 normal); moderately alkaline (pH 8.1); clear smooth boundary.

Bssky—80 to 87 inches; yellowish brown (10YR 5/4) clay, dark yellowish brown (10YR 4/4) moist; few fine greenish gray (5GY 5/1) moist irregular iron depletions; moderate coarse subangular blocky structure; very hard, firm, deformable, sticky and plastic; few very fine roots throughout; few fine tubular pores; prisms break to wedge-shaped peds; iron depletions are along pore linings or on surfaces of slickensides; common prominent continuous intersecting slickensides on faces of peds; common fine irregular white (10YR 8/1) soft masses of lime throughout and common fine threads white (10YR 8/1) soft masses of gypsum throughout and common fine rounded very dark gray (10YR 3/1) iron-manganese concretions throughout; violently effervescent on concretions (HCL, 1 normal); strongly alkaline (pH 8.7).

Type location: Colusa County, California; located about 3 miles west of Colusa; 2200 feet north and 2250 feet west of the southeast corner of section 27, T. 16 N., R. 2 W., MDB&M; 39 degrees, 12 minutes, 40 seconds north latitude and 122 degrees, 4 minutes, 55 seconds west longitude; USGS Colusa, California topographic quadrangle.

The mean annual soil temperature is 63 to 65 degrees F. The soil temperature is above 47 degrees F. the entire year. The soil moisture control section, 6 to 17 inches, is dry in all parts from May 15 to October 31 unless irrigated and is moist in some or all parts from November 1 to May 15. The weighted average clay content of the textural control section, 10 to 40 inches, ranges from 40 to 60 percent.

The A horizon is 10YR 6/2, 6/1, 5/2, 5/1; 2.5Y 5/2, 4/2. Moist color is 10YR 3/2, 3/1; 2.5Y 3/2. Texture is silty clay. Reaction is slightly acid to moderately alkaline.

The Bw, Bssy and Bssky horizons have is 10YR 6/4, 6/3, 5/4, 5/3; 2.5Y 6/4, 5/2. Moist color is 10YR 4/4, 4/3, 3/4,3/3; 2.5Y 4/4, 4/2, 3/2. Texture is silty clay or clay. Reaction is slightly to strongly alkaline.