LOCATION COSHO                   WA

Established Series
Rev. CAB/SBC
12/2022

COSHO SERIES

The Cosho series consists of moderately deep, well drained soils formed in volcanic ash and glacial drift on valley walls and bedrock benches. Slopes are 10 to 50 percent. The mean annual precipitation is about 1,700 millimeters. The mean annual temperature is about 9 degrees C.

TAXONOMIC CLASS: Ashy over sandy or sandy-skeletal, amorphic over isotic, frigid Typic Udivitrands

TYPICAL PEDON: Cosho gravelly ashy sandy loam, on a bedrock bench landform with a SE facing slope of 35 percent at 762 meters elevation under coniferous forest vegetation. When described on September 6, 2006 the soil was slightly moist throughout. (Colors are for moist soil unless otherwise noted.)

Oi--0 to 6 cm; slightly decomposed plant material; common very fine, fine, and medium roots; clear wavy boundary.

Oe--6 to 14 cm; moderately decomposed plant material; many very fine and medium and few very fine, coarse and very coarse roots; abrupt irregular boundary.

E--14 to 15 cm; very dark grayish brown (10YR 3/2) gravelly ashy sandy loam, light brownish gray (10YR 6/2) dry; weak fine subangular blocky structure; soft, very friable, nonsticky, nonplastic; common very fine and fine and few medium roots; 10 percent fine gravel and 5 percent medium and coarse gravel; very strongly acid (pH 4.8); abrupt wavy boundary.

Bw--15 to 53 cm; dark yellowish brown (10YR 3/4) gravelly ashy sandy loam, yellowish brown (10YR 5/4) dry; moderate medium subangular blocky structure; soft, very friable, nonsticky, nonplastic; few very fine, fine, coarse, and very coarse and common medium roots; 10 percent fine gravel and 15 percent medium and coarse gravel; moderately acid (pH 5.6); clear wavy boundary.

2BC--53 to 75 cm; dark yellowish brown (10YR 3/4) very gravelly loamy sand, dark yellowish brown (10YR 4/4) dry; moderate medium subangular blocky structure; soft, very friable, nonsticky, nonplastic; few very fine, fine, medium, and coarse; 10 percent fine gravel, 20 percent medium and coarse gravel, and 15 percent cobbles; moderately acid (pH 5.9); gradual wavy boundary.

2C--75 to 90 cm; olive brown (2.5Y 4/3) very gravelly loamy sand, light olive brown (2.5Y 5/3) dry; weak medium subangular blocky structure; soft, very friable, nonsticky, nonplastic; few fine roots; 15 percent fine gravel, 15 percent medium and coarse gravel, and 15 percent cobbles; moderately acid (pH 6.0).

2R--90 cm; metavolcanic bedrock.

TYPE LOCATION: North Cascades National Park, Whatcom County, Washington; 34 meters west and 141 meters south of NE corner of Section 30, T37N, R12E Willamette Meridian; Mount Triumph, Washington USGS quadrangle; 48 degrees, 40 minutes, 7 seconds north latitude, 121 degrees, 16 minutes, 53 seconds west longitude; NAD83; UTM 626540 meters E, 5392037 meters N, zone 10.

RANGE IN CHARACTERISTICS:
Mean annual soil temperature: 6 to 8 degrees C. Frigid soil temperature regime.
Soil moisture control section: dry for less than 45 consecutive days from June to October. Udic soil moisture regime.
Thickness of volcanic ash mantle: 38 to 83 centimeters
Depth to bedrock (lithic contact): 50 to 100 centimeters
The particle-size control section in this soil is contrasting. Most characteristics are listed by horizon.

E horizon:
Hue - 7.5YR or 10YR
Value - 3 to 5 moist, 5 to 7 dry
Chroma - 1 to 3 moist or dry
Fine earth texture - ashy FSL, ashy SL, or ashy LS
Rock fragments - 0 to 30 percent total
0 to 25 percent gravel
0 to 10 percent cobbles
0 to 5 percent stones
Clay content - 1 to 8 percent
Volcanic glass - 15 to 50 percent
Reaction - extremely acid to strongly acid
Thickness - 1 to 13 centimeters

Bw horizon:
Hue -7.5YR or 10YR
Value - 3 to 4 moist, 5 to 6 moist
Chroma - 3 to 6 moist or dry
Fine earth texture - ashy FSL or ashy SL
Rock fragments - 10 to 30 percent total
10 to 30 percent gravel
0 to 15 percent cobbles
0 to 5 percent stones
Clay content - 3 to 8 percent
Volcanic glass - 15 to 50 percent
Reaction - strongly acid to moderately acid
Thickness - 38 to 70 centimeters

2BC horizon:
Hue -10YR or 2.5Y
Value - 3 to 5 moist, 4 to 6 moist
Chroma - 4 to 6 moist or dry
Fine earth texture - COSL, LS, or LCOS
Rock fragments - 35 to 80 percent total
25 to 55 percent gravel
10 to 20 percent cobbles
0 to 10 percent stones
Clay content - 1 to 6 percent
Volcanic glass - 5 to 15 percent
Reaction - moderately acid to slightly acid
Thickness - 0 to 35 centimeters

2C horizon:
Hue -2.5Y or variegated
Value - 4 to 5 moist, 5 to 6 moist
Chroma - 3 or 4 moist or dry
Fine earth texture -LS, LCOS, or S
Rock fragments - 40 to 90 percent total
30 to 65 percent gravel
10 to 25 percent cobbles
0 to 10 percent stones
Clay content - 0 to 6 percent
Volcanic glass - 0 to 10 percent
Reaction - moderately acid to slightly acid

COMPETING SERIES: These are the Caribouridge, Garveson, and Hysing soils. The Caribouridge soils have glassy over mixed mineralogy and ashy silt loam textures in the upper part of the particle-size control section. Garveson soils are very deep and have ashy silt loam textures in the upper part of the particle-size control section. Hysing soils have ashy silt loam textures in the upper part of the particle-size control section and a paralithic contact at 105 to 140 cm.

GEOGRAPHIC SETTING: The Cosho soils are on bedrock benches and valley walls, at elevations of 230 to 780 meters. Slopes are 10 to 50 percent. These soils formed in mixed volcanic ash and glacial drift over glacial drift. The climate consists of cool, dry summers and cold, wet winters. Mean annual precipitation ranges from 1,700 to 2,500 millimeters, and mean annual air temperature ranges from 5 to 10 degrees C. Frost-free season is 60 to 90 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Ledeir (T), Benzarino, and Thorton (T) soils. Ledeir soils form on the more stable portions of the same landforms, have spodic horizons, and are very deep to bedrock. Benzarino soils form on less stable portions of the same landforms and have a lithic contact within 50 cm. Thorton soils form on the same landforms, are ashy over loamy-skeletal, and are very deep to bedrock.

DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY: Well drained; high to very high saturated hydraulic conductivity.

USE AND VEGETATION: Used for watershed, recreation, woodland, and wildlife habitat. Potential natural vegetation consists of western hemlock, Douglas-fir, and western redcedar with an understory of vine maple, Oregon-grape, serviceberry and, twinflower.

DISTRIBUTION AND EXTENT: Western slopes of the North Cascade Mountains, Washington. MLRA 3. Series is of moderate extent.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon

SERIES ESTABLISHED: North Cascades National Park Service Complex soil survey, 2011.

REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon: 0 to 18 centimeters (Oi, Oe, E, and upper 3 centimeters of the Bw horizon)
Albic horizon: 14 to 15 centimeters (E horizon)
Cambic horizon: 15 to 53 centimeters (Bw horizon)
Andic soil properties: 14 to 53 centimeters (E and Bw horizons)
Lithologic discontinuity: 53 centimeters
Lithic contract: 90 centimeters (2R horizon)
Particle size-control section: 14 to 114 centimeters (0 to 100 centimeters from the mineral surface)

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National Cooperative Soil Survey
U.S.A.