LOCATION ACO CA
Established Series
Rev. NEE-LCL-RCH-ET
04/2015
ACO SERIES
The Aco series consists of very deep, well to somewhat excessively drained soils that formed in mixed alluvium on terraces slightly above the flood plain. Slopes are 0 to 8 percent. The mean annual precipitation is about 4 inches and the mean annual air temperature is about 72 degrees F.
TAXONOMIC CLASS: Coarse-loamy, mixed, superactive, hyperthermic Typic Haplocalcids
TYPICAL PEDON: Aco sandy loam - native shrubs (Colors are for dry soil unless otherwise noted.) Surface pavements of very coarse sand and gravel up to 3 inches in diameter. Some pebbles have weak desert varnish and some are imbedded to 1/2 inch into the soils surface.
A1--0 to 3 inches; pinkish gray (7.5YR 7/2) sandy loam, brown (7.5YR 5/4) moist; strong fine medium, thick and very thick platy structure; slightly hard, very friable, nonsticky, nonplastic; few fine roots; many very fine discontinuous vesicular pores; few colloidal coatings on sand grains; slightly effervescent; moderately alkaline (pH 8.4); clear wavy boundary. (2 to 5 inches thick)
Bk1--3 to 18 inches; Light brown (7.5YR 6/4) coarse sandy loam, strong brown (7.5YR 5/6) moist; massive; soft, very friable, nonsticky, nonplastic; few very fine and medium roots; few very fine open vesicular pores in upper portion of horizon and common very fine tubular pores throughout; few colloidal coatings and stains on mineral grains; violently effervescent with about 7 percent by volume of medium to large, irregular lime concretions; moderately alkaline (pH 8.2); diffuse irregular boundary. (12 to 18 inches thick)
Bk2--18 to 46 inches; light brown (7.5YR 6/4) sandy loam, brown (7.5YR 5/4) moist; massive; slightly hard, very friable, slightly sticky, nonplastic; common very fine pores; few colloidal coatings and stains on mineral grains; violently effervescent with about 9 percent by volume of medium to large, irregular lime concretions; moderately alkaline (pH 8.2); gradual wavy boundary. (26 to 30 inches thick)
C--46 to 60 inches; very pale brown (10YR 7/4) fine sand, light yellowish brown (10YR 6/4) moist; single grained; loose; violently effervescent, lime on bottoms of some rock fragments near top of the horizon; moderately alkaline (pH 8.0).
TYPE LOCATION: Riverside County, California; about 1,180 feet south and 335 feet west of monument in NE corner of sec. 2, T. 6 S., R. 22 E.
RANGE IN CHARACTERISTICS: At a depth of 20 inches the mean winter soil temperature is about 57 F, the mean summer soil temperature is about 96 F, and the mean annual soil temperature about 74 F. Gravel content ranges from 1 to 20 percent, except the immediate surface pavement may have more than 20 percent. The soils are usually dry and are calcareous throughout. Organic matter content is less than 0.5 percent and decreases regularly with depth. The undisturbed surface has a weak to moderate pavement of pebbles that usually have a weak desert varnish.
The A horizon has hue of 7.5YR or 10YR, dry value of 6 to 7 or rarely 8; moist value or 5 or 6, dry chroma of 2 through 5, and moist chroma of 4 through 6. It ranges from fine sand to fine sandy loam. In undisturbed areas, it has weak to strong platy structure and in tilled areas it is massive or single grained. This horizon is soft to slightly hard. It ranges in pH from about 7.9 to 8.4. It is slight to violently effervescent which is stronger on the surface of plates than on broken edges.
The Bk horizon ranges slightly lighter or slightly redder than the A horizon, but has essentially the same color range slightly lighter or slightly redder than the A horizon. The 10 to 40 inch zone is coarse sandy loam or sandy loam and has less than 18 percent clay. The Bk horizon commonly is massive, but ranges to having weak structure. It is soft to slightly hard. Lime accumulations in the form of soft masses, concretions and coatings on pebbles occur less than 10 inches below the surface and some secondary lime continues to a depth of 40 inches or more. Calcium carbonate equivalent is 5 to 15 percent.
Generally, the C horizons below 45 to 65 inches consist of loose, fine sand.
COMPETING SERIES: These are the
Coolidge,
Laveen,
Rillito and
Toltec series. The Coolidge, Laveen, Rillito and Toltec soils are intermitantly moist within the moisture control section during July through September. In addition the Laveen soilsare loam and very fine sandy loam in the control section, Rillito soils have 15 to 35 percent gravel and Toltec soils have coarse fragments consisting of pan fragments.
GEOGRAPHIC SETTING: Aco soils are on terraces slightly above the flood plain at elevations of 30 to about 1,000 feet. Slopes are less than 8 percent and usually less than 2 percent. The soils formed in relatively young coarse and moderately coarse textured alluvium from a wide variety of rocks. The climate is arid with an average annual precipitation of about 4 inches that occurs as gentle winter rains or as erratic high intensity summer storms. The average July temperature is about 92 F, the average January temperature is about 53 F, and the mean annual temperature is about 72 F. The frost-free season is about 290 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the
Carrizo,
Chuckawalla,
Cibola,
Holtville,
Imperial,
Orita,
Ripley, and Thermal soils and the competing
Indio, Mecca, and
Meloland soils. All of these soils except Chuckawalla and Orita occur on flood plains at slightly lower elevations than Aco and lack lime segregations. Chuckawalla and Orita soils are generally at slightly higher elevations and have argillic horizons.
DRAINAGE AND PERMEABILITY: Well to somewhat excessively drained; permeability is moderately rapid. Runoff is mostly low, a few more sloping areas may have medium runoff.
USE AND VEGETATION: In recent years some areas have been brought under irrigation and are used for growing citrus, alfalfa, and melons. Principal native plants are creosotebush, white bursage, and a few minor annuals.
DISTRIBUTION AND EXTENT: Aco soils have been mapped along the lower Colorado River in California and may occur in Arizona. They are moderately extensive in MLRA 31.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: PHOENIX, ARIZONA
SERIES ESTABLISHED: Riverside County, California, 1971.
REMARKS: Diagnostic horizons and features recognized in the profile:
1. Calcic horizon -- 3 to 46 inches (BK1 and Bk2)
The Aco soils have previously classified as Typic Torriorthents and as Red Desert soils.
Last revised by the state on 5/98.
National Cooperative Soil Survey
U.S.A.