LOCATION COTATI             CA
Established Series
REV: DFW-JMK-DJE-ET
02/2003

COTATI SERIES


The Cotati series consists of deep and very deep, moderately well drained soils formed in material weathered from soft sedimentary rocks. Cotati soils are on terraces and have slopes of 2 to 30 percent. The mean annual precipitation is 30 inches and the mean annual temperature is 59 degrees F.

TAXONOMIC CLASS: Fine, mixed, active, thermic Ultic Palexeralfs

TYPICAL PEDON: Cotati fine sandy loam - on a southeast facing slope of 4 percent in dryland pasture at 190 feet elevation. (Colors are for dry soil unless otherwise stated).

Ap--0 to 5 inches; light brownish gray (10YR 6/2) fine sandy loam, very dark grayish brown (10YR 4/2) moist; weak fine granular structure in surface inch, massive below with apparent compaction by livestock; hard, friable, slightly sticky and nonplastic; many very fine and few fine roots; common very fine interstitial pores; strongly acid (pH 5.5); clear wavy boundary. (4 to 10 inches thick)

A1--5 to 11 inches; grayish brown (2.5Y 5/2) fine sandy loam, dark grayish brown (10YR 4/2) moist; massive; slightly hard, friable, slightly sticky and nonplastic; many very fine and few fine roots; many very fine tubular, many very fine and fine interstitial pores; common worm casts; strongly acid (pH 5.3); clear wavy boundary. (4 to 12 inches thick)

A2--11 to 19 inches; light brownish gray (2.5Y 6/2) fine sandy loam, dark grayish brown (10YR 4/2) moist; massive; slightly hard, friable, slightly sticky and slightly plastic; many very fine roots; many very fine tubular, many very fine and fine interstitial pores; common worm holes and casts; some mixing of E horizon into this horizon by worm activity; strongly acid (pH 5.1); clear wavy boundary. (6 to 12 inches thick)

El--19 to 22 inches; light gray (5Y 7/2) sandy loam, grayish brown (2.5Y 5/2) moist; massive parting to single grain: slightly hard, friable, slightly sticky and slightly plastic; many very fine and few fine roots; many very fine tubular and many very fine and fine interstitial pores; common worm holes and casts; some mixing of A2 into this horizon by worm activity; strongly acid (pH 5.3); abrupt wavy boundary. (2 to 10 inches thick)

Bt1--22 to 35 inches; grayish brown (10YR 5/2) clay, light olive brown (2.5Y 5/4) moist; moderate coarse prismatic structure; very hard, very firm, sticky and very plastic; many very fine roots; many very fine tubular pores; continuous moderately thick clay films on peds and in tubular pores; common compression faces and slickensides; very strongly acid (pH 4.5); gradual wavy boundary. (10 to 20 inches thick)

Bt2--35 to 48 inches;light brownish gray (2.5Y 6/2) clay, pale olive (5Y 6/3) moist; weak coarse prismatic structure but prisms break diagonally along slickenside planes; very hard, firm and very firm, sticky and very plastic; few very fine roots; common very fine tubular pores; moderately thick clay films in pores nand on peds; common compression faces and slickensides; extremely acid (pH 4.0); clear wavy boundary. (6 to 18 inches thick)

Bt3--48 to 55 inches;light gray (2.5Y 7/2) clay, olive (5Y 5/3) moist; massive; very hard, friable and firm, very sticky and very plastic; very few very fine roots; few very fine tubular pores; thick clay films in pores; few slickensides; extremely acid (pH 4.2); gradual wavy boundary. (6 to 12 inches thick)

C--55 to 68 inches; light gray (5Y 7/2) clay, olive gray (5Y 5/2) with streaks of dark brown (10YR 3/3) moist; massive; very hard, firm and friable, very sticky and plastic; no roots; common very fine tubular pores; common moderately thick and thick clay films in pores and bridging mineral grains; very strongly acid (pH 4.5); few brittle areas in this horizon probably indicative of irregular transition to weakly consolidated shale or siltstone.

TYPE LOCATION: Sonoma County, 2.5 miles northwest of Cotati, on Maffia Brothers Ranch about 200 feet northwest of junction of driveway and Gravenstein Highway, in the NW 1/4, NW 1/4, section 28, T.6 N., R.8 W.

RANGE IN CHARACTERISTICS: Depth to weakly consolidated shale or siltstone ranges from 40 to more than 60 inches. The mean annual soil temperature varies from 59 to 63 degrees F. The base saturation ranges from 35 to 50 percent throughout. Between a depth of 6 to 18 inches the soil is dry in all parts from July to October, and is moist in all parts from December thru April in most years. Gravel content ranges from 0 to 10 percent throughout the profile.

The A horizon is 10YR 5/2, 6/1, 6/2, 2.5Y 5/2, 6/1 or 6/2 dry. It is fine sandy loam or loam with 10 to 25 percent clay. It is medium through very strongly acid.

The Bt horizon is 10YR 5/2, 5/3, 6/2, 2.5Y 5/2, 5/3 or 7/2. Moist colors are 2.5Y 5/4, 5Y 5/3 or 6/3. It is clay and sandy clay with 40 to 50 percent clay. It is strongly through extremely acid.

The C horizon is 5Y 7/1 or 7/2. Moist colors are 5Y 5/2 or 4/2 with streaks of 10YR 3/2 or 3/3. It is strongly or very strongly acid.

COMPETING SERIES: These are the Forbesville and Redvine series. Forbesville and Redvine soils have hues of 7.5YR or redder throughout and a base saturation of 50 to 75 percent.

GEOGRAPHIC SETTING: The Cotati soils occur on undulating to smooth terraces with slopes of 2 to 30 percent. The soils formed in old sediments of weakly consolidated sandstone, siltstone, and shale, interbedded with clayey materials and conglomerates at elevations of 60 to 800 feet. The climate has hot dry summers and cool moist winters. Mean annual precipitation varies from 20 to 30 inches. Mean annual temperature is 59 degrees F, mean January temperature is 47 degrees F, and mean July temperature is 66 degrees F. Frost-free season varies from 230 to 260 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Clear Lake, Goldridge, Sebastopol and Steinbeck soils. Clear Lake soils lack an argillic horizon and are montmorillonitic. Goldridge soils are fine-loamy and isomesic. Steinbeck soils are fine-loamy and mesic. Sebastopol soils are mesic and have base saturation less than 35 percent.

DRAINAGE AND PERMEABILITY: Moderately well drained; slow to rapid runoff; moderately rapid over very slow permeability.

USE AND VEGETATION: Used for pasture and hay, Christmas tree production and small orchards. Vegetation in uncultivated areas is annual grasses and forbs with scattered live oak and black oak.

DISTRIBUTION AND EXTENT: Northern and Central Coastal California. The soils are moderately extensive.

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

SERIES ESTABLISHED: Alameda County, California 1963.

REMARKS: This is a classification change from fine, mixed, mesic Ultic Palexeralfs to fine, mixed, thermic Ultic Palexeralfs.

Diagnostic horizons and features are as follows:

1. Ochric epipedon - 0 to 22 inches (Ap, A1, A2, E); ranges from 16 to 30 inches thick. Clay content by field estimates is 18 percent. Organic matter is assumed to be less than 1 percent and decreases with depth. B.S. is assumed to be between 35 to 50 percent.

2. Argillic horizon - 22 to 55 inches (Bt1, Bt2, Bt3); ranges from 28 to 50 inches thick. B.S. by grab sample was between 35 to 50 percent. The Textural control section is 22 to 42 inches or the top 20 inches of the argillic horizon. Clay content by field estimates of the textural control section was 43 percent.

3. Mixed mineralogy--by assumption--no cracks to indicate montmorillonitic.

4. Soil temperature 59 to 62 degrees F, based on similar soils in area--all data from other surveys in area show similar grassland soils to be thermic not mesic.

5. Soil moisture in control section.

Moist in some parts soil temperature greater than 41 degrees F--259 days (71 percent of time).

Moist in some parts soil temperature more than 46 degrees F. (3/1-6/15) 107 days.

Last revised by the state on 6/88.


National Cooperative Soil Survey
U.S.A.