Established Series


The Sehorn series consists of moderately deep, well drained soil on foothills. These soils formed in residuum weathered from calcareous sandstone and shale. Slope ranges from 2 to 75 percent. The mean annual precipitation is about 25 inches and the mean annual temperature is about 61 degrees F.

TAXONOMIC CLASS: Fine, smectitic, thermic Aridic Haploxererts

TYPICAL PEDON: Sehorn clay loam, rangeland. (Colors are for dry soil unless otherwise noted.)

A1--0 to 7 inches; pale brown (10YR 6/3) clay loam, dark brown (10YR 4/3) moist; moderate medium subangular blocky structure; hard, friable, sticky and plastic; common fine roots; slightly acid in upper part, neutral in lower part; abrupt wavy boundary. (4 to 10 inches thick)

Bss1--7 to 15 inches; brown (10YR 5/3) clay, dark brown (10YR 4/3) moist; moderate and strong very coarse subangular blocky structure; very hard, firm, very sticky; common medium and fine roots; common slickensides; neutral; clear wavy boundary. (8 to 10 inches thick)

Bss2--15 to 29 inches; brown (10YR 5/3) clay, dark brown (10YR 4/3) moist; moderate very coarse subangular blocky structure; very hard, firm, sticky; common roots; few shale fragments in lower part; common slickensides; neutral in upper part, slightly alkaline in lower part; gradual irregular boundary. (6 to 24 inches thick)

R--29 to 32 inches; grayish brown, shattered shale and fine grained sandstone.

TYPE LOCATION: Glenn County, California; 2 1/2 miles southeast of Newville; in the SE1/4 section 14, T.22 N., R.6 W.

RANGE IN CHARACTERISTICS: Depth to the bedrock is 20 to 40 inches. The mean annual soil temperature at a depth of 20 inches ranges from 60 to 63 degrees F. Cracks 3/8 to 1 inch wide develop in the soil during late May and June and cracks remain open until October and November. Cracks remain closed during the rest of the year. Cracks extend from the surface to a depth of 20 inches or down to shale bedrock.

The A horizon is 10YR 6/2, 6/3, 5/4, 4/4, 5/3; 2.5Y 5/2, 5/3, 5/4; 5Y 5/2. Moist 10YR 4/4, 4/3, 3/3; 2.5Y 4/2, 4/3; 5Y 4/3. Texture is silty clay, silty clay loam, clay loam or clay. This horizon usually has moderate to strong prismatic angular blocky or subangular blocky structure, but some pedons have granular or platy structure. Reaction is slightly acid to moderately acid.

The Bss horizons generally have colors as listed above, although value may be little higher or a little lower than in the A horizon. These horizons are clay or silty clay with an average of 40 to 60 percent clay. There is a small increase in clay content from upper horizons to lower horizons, but clay films are lacking. Few to common intersecting slickensides are present, but strong evidence of churning is absent. Reaction ranges from neutral to moderately alkaline. Some pedons have lime with segregations just above the bedrock or in fractures in the upper part of the bedrock.

COMPETING SERIES AND THEIR DIFFERENTIAE: These are the Alo, Altamont, Auld, Balcom, Capay, Castaic, Centerville, Cibo, Myers, Nacimiento, Porterville, and Seville soils. Altamont, Auld, Capay, Centerville, Cibo, Porterville, and Seville soils have moist value of 3 throughout the upper 12 inches or more of the profile. Also, Capay, Porterville, Seville, and Myers soils lack lithic or paralithic contacts. Balcom, Castaic, and Nacimiento soils lack slickensides and have less than 35 percent clay in the control section.

GEOGRAPHIC SETTING: The Sehorn soils occur on gently sloping to very steep uplands under grass and oaks. Slopes are 2 to 75 percent. Elevations are 200 to 2,000 feet. The climate is subhumid, with hot, dry summers and cool, moist winters. The mean annual precipitation is 14 to 35 inches. The mean annual temperature is about 58 to 64 degrees F.; the average January temperature is 42 degrees F.; and the average July temperature is 75 degrees F. The frost free season is about 200 to 300 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Altamont and Balcam soils, and the Contra Costa, Dibble, and Millsholm soils. Contra Costa and Dibble soils have argillic horizons. Millsholm soils have bedrock at depths of less than 20 inches.

DRAINAGE AND PERMEABILITY: Well drained; low to very high runoff; slow permeability.

USE AND VEGETATION: Used for grazing with a few areas of gently sloping soils used for dryland grain. Natural vegetation is annual grasses and forbs with blue oaks and shrubs.

DISTRIBUTION AND EXTENT: Foothills of the eastern slopes of the northern Coast Range, California. The soils are moderately extensive.


SERIES ESTABLISHED: Glenn County, California, 1957.


Series reclassified May 1996. Competing series not reviewed at that time.

Series updated 8-20-96: Runoff old terminology, medium to very rapid changed to new terminology low to very high.

ADDITIONAL DATA: Colusa County, NSSL Pedon 94P-50, S93CA-011-022 at 39 degrees North latitude, 20 minutes, 44 seconds, 122 degrees west longitude, 19 minutes, 23 seconds.

National Cooperative Soil Survey