Established Series
Rev. RCH


The El Peco series is a member of a coarse loamy, mixed thermic family of Typic Durorthids. The soils have very pale brown, strongly alkaline, fine sandy loam A horizons, similar C horizons overlying a strongly lime-silica cemented duripan.

TAXONOMIC CLASS: Coarse-loamy, mixed, superactive, thermic Entic Durixerepts

TYPICAL PEDON: El Peco fine sandy loam - annual grass pasture.

A--0 to 8 inches; very pale brown (10YR 7/3) fine sandy loam, grayish brown (2.5Y 5/2) moist; massive; hard, friable, slightly sticky; slight amount of lime disseminated through horizon; few fine roots; organic matter content very low; strongly alkaline (pH 8.5); abrupt wavy boundary. (4 to 12 inches thick).

C1--8 to 14 inches; very pale brown (10YR 7/3) fine sandy loam; grayish brown (2.5Y 5/2) moist; massive; hard, firm, slightly sticky; moderate amount of disseminated lime; soil material is compact and does not readily slake in water; strongly alkaline (pH 8.5); clear wavy boundary. (4 to 6 inches thick).

C2--14 to 38 inches; very pale brown (10YR 7/3) fine sandy loam; light olive brown (2.5Y 5/4) moist; massive; slightly hard, friable, slightly sticky; irregularly shaped, discontinuous areas of compaction, 1 to 3 inches in size, similar in character to horizon above; areas of compaction are hard, firm and slightly sticky; moderate amount of disseminated lime; strongly alkaline (pH 8.5); abrupt smooth boundary. (10 to 24 inches thick).

C3mca--38 to 43 inches; light gray (2.5Y 7/2) strongly lime-silica cemented duripan of silty texture, slightly darker, thin (1/8") cemented layer on surface of duripan; grayish brown (2.5Y 5/2) moist; coarse platy structure to massive; very few pores; strongly alkaline (pH 8.5); clear smooth boundary. (1 to 5 inches thick).

C4--43 inches +; light gray (2.5Y 7/2) very compact silty substratum; light olive brown (2.5Y 5/4) moist; very weak medium to fine platy structure to massive; hard to very hard, very firm; few fine pores; slightly calcareous; strongly alkaline (pH 8.5); continues to indefinite depth but interstratified with softly consolidated coarser materials of variable thickness.

TYPE LOCATION: Madera County, California; near center SE 1/4 Sec. 28, T. 12S., R.15E., 0.6 miles SE of junction of Avenue 7 and Firebaugh Boulevard, on Avenue 7.

RANGE IN CHARACTERISTICS: El Peco soils have ochric epipedons and duripans. Depth to the duripan ranges from 18 to 36 inches and is modally 24 inches. Extremes range from 6 to 60 inches but this is usually because of cuts and fills made in land leveling. The soils are usually dry between 10 and 40 inches; have mean soil temperatures greater than 59 degrees F., and have mixed mineralogy.

The A horizons range in color from very pale brown, pale brown, and light brownish gray in 2.5Y and 10YR hues; texture is fine sandy loam; reaction is moderately to very strongly alkaline and slightly calcareous.

The upper C horizon ranges in color from very pale brown, pale brown, light gray and light brownish gray in 10YR and 2.5Y hues; in texture is fine sandy loam; in reaction from strongly to very strongly alkaline. This horizon may have some compacted, weakly cemented areas that are discontinuous and 1 to 3 inches in size.

The Cm horizon is strongly cemented with lime and silica, but less than half the volume is destroyed by acid. The color is light brownish gray to light gray and there may be yellowish, brown or reddish mottles in places. The duripan often consists of a series of layers 1 to 4 inches in thickness separated by uncemented material that is silty, loamy or sandy. Degree of cementation is variable but usually decreases with depth.

COMPETING SERIES: There are no other series in the same family. In the subgroup there are the Crebbin soils which have soil temperatures less than 59 degrees F. and the Stewart which is in a fine loamy family. Similar soils are the Fresno soils which have argillic horizons over the duripan and Pozo soils which have mollic epipedons.

SETTING: The El Peco soils occur on nearly level to slightly depressed areas of old alluvial fans lying in the basin rim zone of large valley troughs. The microrelief is irregular low hummocky. The soils are developed in alluvium from granitic rock. They occur at elevations of 100 to 300 feet in a subhumid, mesothermal climate with mean annual rainfall of 8 to 9 inches, with hot, dry summers and cool, moist winters. Mean annual temperature is about 63 degrees F., average January temperature about 45 degrees F., and average July temperature about 82 degrees F.

PRINCIPAL ASSOCIATED SOILS: These include the Chino, Dinuba, and Traver soils which lack duripans.

DRAINAGE AND PERMEABILITY: Somewhat poorly drained with very slow permeability and slow to very slow runoff.

USE AND VEGETATION: Used mainly for dry pasture for livestock. Where reclaimed, cotton, alfalfa and irrigated pasture are grown with fair success. Vegetation consists of annual grasses, forbs, salt and alkali-tolerant plants--salt grass, alkali sacaton, inkweed, alkali heath, coyote thistle, jackass clover.

DISTRIBUTION AND EXTENT: Central San Joaquin Valley, California. The soils are moderately extensive, comprising 15,000 acres in Fresno and Madera Counties.


SERIES ESTABLISHED: Madera Area, California, 1959. (Source of name is El Peco Ranch, Madera County, California.)

REMARKS: The soils were formerly classified in the Alluvial group.

OSED scanned by SSQA. Last revised by state on 6/2/66.

National Cooperative Soil Survey