LOCATION ARCO IDEstablished Series
TAXONOMIC CLASS: Fine-silty, mixed, superactive, frigid Aquic Calcixerolls
TYPICAL PEDON: Arco silt loam, pastureland; on a 0 percent slope at 5,320 feet elevation. When described on May 3, 1975, the soil was moist throughout. (Colors are for dry soil unless otherwise noted.)
A--0 to 4 inches; gray (10YR 5/1) silt loam, very dark gray (10YR 3/1) moist; moderate medium platy structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine and few fine roots; common very fine tubular pores; strongly effervescent; moderately alkaline (pH 8.0); clear wavy boundary. (3 to 6 inches thick)
Bw--4 to 15 inches; gray (10YR 5/1) silt loam, very dark gray (10YR 3/1) moist; weak fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine roots; common very fine and few fine tubular pores; strongly effervescent; moderately alkaline (pH 8.0); gradual wavy boundary. (8 to 14 inches thick)
Bk--15 to 26 inches; light brownish gray (10YR 6/2) silt loam, dark grayish brown (10YR 4/2) moist; weak fine and medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine and few fine and medium roots; many very fine tubular pores; strongly effervescent; moderately alkaline (pH 8.0); abrupt wavy boundary. (8 to 41 inches thick)
Bkg1--26 to 32 inches; light gray (5Y 6/1) silt loam, gray (5Y 5/1) moist; few fine faint light yellowish brown (10YR 6/4) moist redoc concentrations; weak fine subangular blocky structure; soft, very friable, slightly sticky and slightly plastic; common very fine and few fine and medium roots; common very fine and many fine tubular pores; violently effervescent; slightly alkaline (pH 7.5); clear wavy boundary. (4 to 12 inches)
Bkg2--32 to 45 inches; gray (5Y 5/1) silt loam, dark gray (5Y 4/1) moist; common medium faint light yellowish brown (10YR 6/4) moist redox concentrations; massive; soft, very friable, slightly sticky and slightly plastic; few very fine, fine, and medium roots; common very fine, many fine, and few medium tubular pores; 50 percent lime veins in matrix; violently effervescent; slightly alkaline (pH 7.4); clear wavy boundary. (10 to 15 inches thick)
Bg--45 to 60 inches; gray (5Y 5/1) silt loam, dark gray (5Y 4/1) moist; common fine faint light yellowish brown (10YR 6/4) moist redox concentrations; massive; soft, very friable, slightly sticky and slightly plastic; few very fine roots; few fine tubular pores; slightly effervescent; slightly alkaline (pH 7.4); abrupt wavy boundary.
TYPE LOCATION: Butte County, Idaho; about 0.5 miles west of Arco; about 1,770 feet south and 420 feet east from the northwest corner of section 36, T.4N., R.26E.
RANGE IN CHARACTERISTICS:
Average annual soil temperature - 43 to 45 degrees F.
Mollic epipedon thickness - 11 to 20 inches
Depth to calcic horizon - 11 to 20 inches
Depth to redox concentrations - 20 to 48 inches
Depth to high water table - 24 to 36 inches
Particle-size control section - averages 22 to 32 percent clay
A horizon
Hue - 10YR or 2.5Y
Value - 4 or 5 dry, 2 or 3 moist
Chroma - 1 or 2 dry or moist
Reaction- slightly or moderately alkaline
Bw horizon
Hue - 10YR or 2.5Y
Value - 4 through 5 dry, 2 or 3 moist
Chroma - 1 or 2 dry or moist
Bk horizon
Hue - 10YR or 2.5Y
Value - 5 through 7 dry, 3 through 5 moist
Chroma - 1 or 2 dry or moist
Texture - SIL or SICL
Bkg and Bg horizons
Hue - 10YR, 2.5Y, or 5Y
Value - 5 through 7 dry, 4 through 6 moist
Chroma - 1 or 2 dry or moist
Texture - SIL, SICL, or GR-L
Reaction - slightly alkaline or moderately alkaline
Coarse fragments - 0 to 25 percent
COMPETING SERIES: There are no other series in the same family.
GEOGRAPHIC SETTING: Arco soils are on stream terraces, flood plains, and basin floors. Slopes range from 0 to 2 percent. Elevations range from 4,700 to 5,900 feet. These soils formed in mixed alluvium. The average annual precipitation is 8 to 12 inches, the average annual air temperature is 41 to 43 degrees F., and the frost-free period is 70 to 90 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Mooretown, Borah, Blackfoot, and Sancrane soils. Mooretown soils are on valley flats, have coarse-loamy particle-size control sections, and have mollic epipedons that are 30 to 60 inches thick. Borah soils are on valley flats, have sandy-skeletal particle-size control sections, and have mollic epipedons that are 20 to 40 inches thick. Blackfoot soils are on flood plains and low terraces and have fine-loamy particle-size control sections. Sancrane soils are on flood plains and stream terraces, are poorly drained, and are 20 to 35 inches to strongly contrasting textures.
DRAINAGE AND PERMEABILITY: Somewhat poorly drained; slow runoff; moderately slow permeability. This soil is occasionally flooded for brief periods in the spring of some years. The drainage of some areas has been altered and is now moderately well drained.
USE AND VEGETATION: Mostly nonirrigated pastureland and hayland. Also used for irrigated cropland, hayland, and pastureland. The natural vegetation is sedges, basin big sagebrush, basin wildrye, rabbitbrush, and streambank wheat grass. Cropland is hay, small grains, and potatoes.
DISTRIBUTION AND EXTENT: East central Idaho. These soils are not extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Custer-Lemhi Counties, Idaho, 1999.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - The zone from the soil surface to 15 inches (A and Bw horizons)
Calcic horizon - The zone from 15 to 45 inches (Bk, Bkg1, and Bkg2 horizons)
Particle-size control section - The zone from 10 to 40 inches (part of the Bw horizon, the Bk and Bkg1 horizons, and part of the Bkg2 horizon)