LOCATION COSKI IDEstablished Series
TAXONOMIC CLASS: Coarse-loamy, mixed, superactive Xeric Haplocryolls
TYPICAL PEDON: Coski gravelly coarse sandy loam - forest; on a 55 percent southwest-facing slope. (Colors are for dry soil unless otherwise noted.)
Oi--0 to 0.5 inch; very dark brown (10YR 2/2) slightly decomposed needles, twigs, and cones; moderately acid (pH 5.8); abrupt wavy boundary. (0 to 3 inches thick)
A1--0.5 to 5 inches; dark grayish brown (10YR 4/2), brown (10YR 5/3) crushed gravelly coarse sandy loam, very dark brown (10YR 2/2), very dark grayish brown (10YR 3/2) crushed moist; weak fine granular structure; slightly hard, very friable; many fine, common medium, and few coarse roots; common very fine tubular pores; 20 percent angular pebbles, mostly less than 5 mm across; moderately acid (pH 6.0); clear wavy boundary. (1 to 6 inches thick)
A2--5 to 15 inches; brown (10YR 5/3) gravelly coarse sandy loam, dark brown (10YR 3/3) moist; weak coarse subangular blocky structure that parts to weak fine granular; slightly hard, very friable; common fine and few medium roots; common very fine tubular pores; 15 percent angular fine and medium pebbles; moderately acid (pH 5.8); clear wavy boundary. (4 to 11 inches thick)
Bw1--15 to 26 inches; light yellowish brown (10YR 6/4), pale brown (10YR 6/3) crushed gravelly coarse sandy loam, brown (10YR 4/3) moist; few 1 to 2-inch diameter spots of browner material associated with grayer spots; weak coarse subangular blocky structure; slightly hard, very friable; common fine and few medium and coarse roots; many very fine tubular pores; 20 percent angular pebbles; very few clay films in some pores and on some coarse fragments; moderately acid (pH 5.9); clear wavy boundary. (8 to 15 inches thick)
Bw2--26 to 40 inches; light yellowish brown (10YR 6/4) gravelly coarse sandy loam, brown (10YR 4/3) moist; common spots of slightly browner material associated with grayer (partially uncoated particles) spots; weak coarse subangular blocky structure; slightly hard, very friable; common fine, few medium and coarse roots; many very fine and few fine tubular pores; 17 percent angular pebbles; very few clay films in some pores and on coarse fragments; moderately acid (pH 5.8); gradual wavy boundary. (7 to 15 inches thick)
C1--40 to 56 inches; light yellowish brown (10YR 6/4) very cobbly loamy coarse sand, dark yellowish brown (10YR 4/4) moist; massive; soft, very friable; few fine and common medium roots; 50 percent angular and subangular cobbles and pebbles; moderately acid (pH 5.8); clear irregular boundary. (2 to 20 inches thick)
C2--56 to 62 inches; yellowish very cobbly coarse sand; single grain; loose; few fine and common medium roots; moderately acid (pH 6.0). (0 to 20 inches thick)
TYPE LOCATION: Boise County, Idaho; SE 1/4 NE 1/4 section 10, T.9N., R.6E.; coordinates from the fiducial center of aerial photograph ELD 22-211 are 0.3 inch south and 1.0 inch west.
RANGE IN CHARACTERISTICS:
Depth to bedrock - 40 to 60 inches or more
Average annual soil temperature - 38 to 44 degrees F
Clay content in control section - 7 to 13 percent
Thickness of mollic epipedon - 10 to 15 inches
Coarse fragments in control section - 10 to 35 percent
A horizon
Value - 4 or 5 dry, 2 or 3 moist
Chroma - 2 or 3
Reaction - slightly or moderately acid
Bw horizon
Value - 5 through 7 dry, 3 through 5 moist
Chroma - 2 through 4
Texture - SL, COSL, GR-COSL, GR-SL
Reaction - slightly or moderately acid
C horizon
Texture - GR-COSL, GRV-COSL, CBV-COSL, CBV-LCOS, CBV-COS, GR-LCOS, GR-COS
COMPETING SERIES: These are the similar Arkson, Branham, Clergern, Dinnen, Lockman, Sawcreek, Sula, and Teoculli series. Arkson and Sula soils lack large amounts of coarse sand in the profile. Branham and Sawcreek soils are 20 to 40 inches deep to bedrock. Clergern and Teoculli soils have less than 15 percent rock fragments in the profile. Dinnen soils lack cambic horizons. Lockman soils are not dry for as much as 45 consecutive days.
GEOGRAPHIC SETTING: Coski soils are in rolling to very steep mountain sideslopes. Slopes range from 10 to 70 percent. Elevation is 4,500 to 8,000 feet. The areas at the lower elevations have northerly slopes. The soils formed in residuum, alluvium and colluvium derived from intermediate intrusive bedrock. Average annual precipitation is 25 to 35 inches and includes 8 to 15 feet of snowfall. The average annual air temperature is 36 to 43 degrees F. The average freeze-free period is about 30 to 80 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Broad Canyon, Koppes, Quartzburg, and Scriver series. The Quartzburg soils have bedrock at 20 to 30 inches and sandy control sections. Quartzburg soils are on south-facing slopes. Broad Canyon, Koppes, and Scriver soils are on landscape positions similar to Coski soils.
DRAINAGE AND PERMEABILITY: Well or somewhat excessively drained; medium or rapid runoff; and moderately rapid permeability.
USE AND VEGETATION: Used for forestry, grazing, wildlife, watershed, and recreation. The natural vegetation is mainly mixed Douglas-fir and ponderosa pine with dominantly ninebark ground cover in most areas. A broken conifer stand with forb-grass cover in openings and abundant tall shrubs, such as maple, serviceberry, mountain ash, aspen, willow, and redstem ceanothus is common in the higher areas.
DISTRIBUTION AND EXTENT: Throughout the Garden Valley Ranger District, Boise County, and other parts of the Idaho Batholith. Moderately extensive.
MLRA OFFICE RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Middle Fork Payette River Area, Boise and Valley Counties, Idaho, 1964.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - the zone from 0 to 15 inches (A horizon).
Cambic horizon - the zone from 15 to 40 inches (Bw horizon).
Particle-size control section - the zone from 10 to 40 inches.