LOCATION COSKI                   ID

Established Series
Rev. CWT/BDG/RJS
02/2016

COSKI SERIES

The Coski series consists of deep and very deep, well drained soils on forested mountain slopes. They formed in slope alluvium and colluvium derived from intermediate intrusive bedrock. Slopes are 10 to 70 percent. The average annual precipitation is about 700 mm, and the average annual air temperature is about 5.6 degrees C.

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 1 cm; very dark brown (10YR 2/2) slightly decomposed needles, twigs, and cones; moderately acid (pH 5.8); abrupt wavy boundary. (0 to 8 cm thick)

A1--1 to 14 cm; 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 gravel, mostly less than 5 mm across; moderately acid (pH 6.0); clear wavy boundary. (3 to 15 cm thick)

A2--14 to 39 cm; 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 gravel; moderately acid (pH 5.8); clear wavy boundary. (10 to 28 cm thick)

Bw1--39 to 67 cm; 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 gravel; very few clay films in some pores and on coarse fragments; moderately acid (pH 5.9); clear wavy boundary. (20 to 38 cm thick)

Bw2--67 to 103 cm; 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 gravel; very few clay films in some pores and on coarse fragments; moderately acid (pH 5.8); gradual wavy boundary. (18 to 38 cm thick)

C1--103 to 144 cm; 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 gravel; moderately acid (pH 5.8); clear irregular boundary. (5 to 50 cm thick)

C2--144 to 159 cm; yellowish very cobbly coarse sand; single grain; loose; few fine and common medium roots; 50 percent angular and subangular cobbles and gravel moderately acid (pH 6.0).

TYPE LOCATION: Boise County, Idaho; SE 1/4 NE 1/4 section 10, T.9N., R.6E.; Latitude - 44 degrees, 7 minutes, 59.57 seconds North; Longitude - 115 degrees, 43 minutes, 36.39 seconds West; NAD83; USGS Quadrangle - Scott Creek, Idaho.

RANGE IN CHARACTERISTICS:
Depth to bedrock - 100 to 150 cm or more
Average annual soil temperature - 3.3 to 7.2 degrees C.
Clay content in control section - 7 to 13 percent
Thickness of mollic epipedon - 25 to 38 cm
Coarse fragments in control section - 10 to 35 percent

A1, A2 horizons
Value - 4 or 5 dry, 2 or 3 moist
Chroma - 2 or 3 dry or moist
Textures - sandy loam, coarse sandy loam
Clay content - 0 to 15 percent
Rock fragments - 0 to 30 percent gravel, 0 to 11 percent cobbles, 0 to 8 percent stones, 0 to 30 percent total rock fragment content
Reaction - 5.6 to 6.5

Bw1, Bw2 horizons
Value - 5 to 7 dry, 3 to 5 moist
Chroma - 2 to 4 dry or moist
Texture - sandy loam, coarse sandy loam
Clay content - 0 to 15 percent
Rock fragments - 5 to 32 percent gravel, 0 to 6 percent cobbles, 5 to 35 percent total rock fragment content
Reaction - 5.6 to 6.5

C1, C2 horizons
Value - 5 to 8 dry, 4 or 5 moist
Chroma - 2 to 4 dry or moist
Texture - coarse sandy loam, loamy coarse sand, coarse sand
Clay content - 0 to 15 percent
Rock fragments - 5 to 35 percent gravel, 0 to 35 percent cobbles, 15 to 60 percent total rock fragment content
Reaction - 5.1 to 6.5

COMPETING SERIES:
Arkson (NV) - do not have a cambic horizon, have textures of loam or fine sandy loam in the C horizons
Lockman (ID) - have a cambic horizon less than 38 cm thick

GEOGRAPHIC SETTING:
Landform - mountain slopes
Elevation - 1,370 to 2,440 meters
Slope - 10 to 70 percent (dominant slopes are 30 to 50 percent)
Aspect - northerly at lower elevations
Parent Material - slope alluvium and colluvium derived from intermediate intrusive bedrock
Mean annual precipitation - 625 to 1,100 mm
Mean annual air temperature - 2.2 to 7.2 degrees C.
Frost-free period - 30 to 90 days

GEOGRAPHICALLY ASSOCIATED SOILS: These are the 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. Koppes and Scriver soils are on landscape positions similar to Coski soils.

DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY: Well or somewhat excessively drained; medium or rapid runoff; and high saturated hydraulic conductivity.

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. About 55,350 acre in extent. MLRA 43B.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) 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 - from 1 to 39 cm (A1, A2 horizons).
Cambic horizon - from 39 to 103 cm (Bw1, Bw2 horizons).
Particle-size control section - from 26 to 101 cm (part of A2, Bw1, part of Bw2 horizons).

ADDITIONAL DATA: Laboratory data exists for a pedon that is taxadjunct to this series. KSSL Lab Pedon No. 79P0346.

Coski soils have a cryic temperature regime and a xeric moisture regime.

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National Cooperative Soil Survey
U.S.A.