LOCATION SUPAN              CA
Established Series


The Supan series comprises Pachic Argixerolls of a fine-loamy mixed, mesic family. The soils have brown, near reddish brown slightly acid sola with loam A horizons, clay loam Bt horizons and gravelly B3 horizons that rest at moderate depths, rather abruptly on partly weathered rock.

TAXONOMIC CLASS: Fine-loamy, mixed, superactive, mesic Pachic Argixerolls

TYPICAL PEDON: Supan loam.

A1--0 to 5 inches; brown (7.5YR 4/3) loam, dark reddish brown (5YR 3/3) moist; weak medium subangular blocky structure; hard, friable, slightly sticky, slightly plastic; abundant very fine and few fine roots; many very fine pores; slightly acid; clear wavy boundary. (4 to 15 inches thick)

A3--5 to 18 inches; brown (7.5YR 4/3) loam, dark reddish brown (5YR 3/3) moist; moderate medium and coarse subangular blocky structure; hard, friable, slightly sticky, slightly plastic; few very fine, fine and medium roots; many very fine pores; few subrounded gravels and cobbles; few thin discontinuous clay films, slightly acid; clear irregular boundary. (5 to 15 inches thick)

B2t--18 to 36 inches; brown (7.5YR 4/3) clay loam, dark reddish brown (5YR 3/3) moist; moderate medium subangular blocky structure; hard or very hard, very firm, sticky, plastic; few very fine, fine and medium roots; few very fine pores; thick continuous clay films mainly in pores; few subrounded cobbles increasing in number with depth; slightly acid; gradual irregular boundary. (10 to 20 inches thick).

B3--36 to 42 inches; brown (7.5YR 5/4) gravelly loam, dark reddish brown (5YR 4/3) moist; massive; hard, friable, slightly sticky, slightly plastic; few roots; few very fine pores; thin continuous clay films in some pores; many partly weathered rock fragments; slightly acid; abrupt irregular boundary. (6 to 20 inches thick)

R--42 + inches; partly weathered but hard volcanic breccia with few, widely spaced, narrow, and nearly vertical cracks.

TYPE LOCATION: Tehama County, California, two miles north, 6 miles east of Paynes Creek. Near the center of NW 1/4 of the NW 1/4 of sec. 19, T. 29 N., R. 2 E.

RANGE IN CHARACTERISTICS: The soils are about neutral or slightly acid throughout although the lower solum may be moderately acid. Soil depth is mostly in the range of 30 inches to 48 inches. Colors are for dry soil; moist colors may be one hue (1/4 letter interval) redder and normally are one or more values darker.

The A horizon is brown or dark brown of 7.5YR or 10YR hue, rarely of 5YR hue; massive, platy, or weak granular; loam or gravelly loam. The transition to the B2t horizon is gradual through an A3 or B1 horizon or both. The B2t horizon most commonly is the same color as the A horizon but may be one unit in value darker and may be 1 or 2 units of chroma higher.

The B2t horizon is heavy clay loam or clay and the structure is subangular blocky. The B3 horizon is the same color as the B2t horizon but has a coarser texture, loam or light clay loam, is nearly massive, and is less porous than the horizons above.

COMPETING SERIES: These include the Auburn, Guenoc, Inks, Parrish, Rescue, and Trabuco series. The Auburn soils are shallow over bedrock and the Guenoc soils have very cobbly or very gravelly clay loam Bt horizons. The Parrish soils have strongly acid Bt horizons. The Rescue soils have yellowish red A horizons and red fine loamy argillic horizons. Trabuco soils have thinner A horizons lower in organic matter, abrupt AB boundaries and are in a thermic family.

GEOGRAPHIC SETTING: The Supan soils occur on sloping, plateau-like areas under shrub-grass vegetation. Underlying rock is andesitic and basaltic tuff-breccia or similar rocks. Elevation range from 1,500 to 4,000 feet. The climate is moist, subhumid mesothermal with mean annual rainfall of 30 to 45 inches, warm dry summer and cool wet winters. Mean annual temperature is about 54 degrees F., average January temperature about 40 degrees F., and average July temperature about 68 degrees F.

GEOGRAPHICALLY ASSOCIATED SOILS: Supan soils occur in the same general area as the Guenoc, Inks, and Toomes soils.

DRAINAGE AND PERMEABILITY: Well drained; medium, to rapid runoff; moderately slowly permeable.

USE AND VEGETATION: Used for grazing. Natural vegetation is grass, oak, digger pine and shrubs.

DISTRIBUTION AND EXTENT: Upper foothills of the Cascade Range, Sierra Nevada Range and in scattered areas of coastal counties in California. The soils are extensive (50,000-100,000 acres).


SERIES ESTABLISHED: Soil survey of Tehama County, California, 1955; name from Supan Ranch, Tehama County.

REMARKS: The Supan series was formerly classified in the Noncalcic Brown group. The present classification is based on a cumulic mollic epipedon, a fine argillic horizon, and a mean annual temperature between 47 degrees and 59 degrees F.

The activity class was added to the classification in February of 2003. Competing series were not checked at that time. - ET

OSED scanned by SSQA. Last revised by state on 5/65.

National Cooperative Soil Survey