LOCATION COURVASH MTEstablished Series
TAXONOMIC CLASS: Ashy over loamy-skeletal, amorphic over mixed, superactive, frigid Alfic Udivitrands
TYPICAL PEDON: Courvash cobbly silt loam, in coniferous forest (colors are for moist soil unless otherwise noted).
Oi--0 to 1 inch; undecomposed and slightly decomposed needles and twigs. (1 to 2 inches thick)
A--1 to 2 inches; very dark brown (10YR 2/2) gravelly ashy silt loam, dark grayish brown (10YR 4/2) dry; moderate fine granular structure; soft, very friable, nonsticky and nonplastic; many very fine and fine and common medium roots; 15 percent pebbles; moderately acid (pH 5.6); abrupt wavy boundary. (1 to 3 inches thick)
Bw1--2 to 10 inches; dark yellowish brown (10YR 3/4) cobbly ashy silt loam, yellowish brown (10YR 5/4) dry; weak very fine granular structure; soft, very friable, nonsticky and nonplastic; common very fine and fine and few medium roots; 10 percent cobbles, 20 percent pebbles; moderately acid (pH 5.6); gradual wavy boundary.
Bw2--10 to 18 inches; dark yellowish brown (10YR 4/4) cobbly ashy silt loam, light yellowish brown (10YR 6/4) dry; weak very fine granular structure; soft, very friable, nonsticky and nonplastic; common very fine and fine and few medium roots; 20 percent cobbles, 10 percent pebbles; moderately acid (pH 5.6); clear smooth boundary. (Combined thickness of the Bw1 and Bw2 horizons is 16 to 25 inches).
2E--18 to 31 inches; pale brown (10YR 6/3) very cobbly loam, very pale brown (10YR 8/3) dry; weak very fine granular structure; slightly hard, friable, nonsticky and nonplastic; few fine and few medium roots; trace stones, 30 percent cobbles, 15 percent pebbles; moderately acid (pH 5.6); gradual wavy boundary. (9 to 15 inches thick)
2Bt/E--31 to 43 inches; Bt part (60 percent) is dark yellowish brown (10YR 4/4) very cobbly loam, light yellowish brown (10YR 6/4) dry; E part (40 percent) is pale brown (10YR 6/3) very cobbly loam, very pale brown (10YR 8/3) dry; weak fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; few fine and medium roots; few distinct clay films on faces of peds and in pores; 5 percent stones, 30 percent cobbles, 15 percent pebbles; moderately acid (pH 5.6); gradual wavy boundary. (7 to 15 inches thick)
2Bt--43 to 60 inches; dark yellowish brown (10YR 4/4) very cobbly clay loam, light yellowish brown (10YR 6/4) dry; moderate fine angular blocky structure; hard, firm, slightly sticky and slightly plastic; few fine and medium roots; common distinct clay films on faces of peds and in pores; 5 percent stones, 35 percent cobbles and 15 percent pebbles; moderately acid (pH 5.6);
TYPE LOCATION: Sanders County, Montana; 200 feet west and 2,400 feet south of the NE corner of sec. 10, T. 27 N., R. 33 W.
RANGE IN CHARACTERISTICS:
Soil temperature - 42 to 45 degrees.
A horizon - Value: 4 or 5 dry; 2 or 3 moist
Chroma: 2, 3 or 4
Clay content: 2 to 10 percent
Volcanic glass content in the 0.02 to 2.0 mm fraction: 12 to 20 percent
Acid-oxalate extractable Al plus 1/2 Fe: 1.60 to 2.25
Phosphate retention: 25 to 75 percent
15-bar water retention on air dried samples: 8 to 12 percent
Bulk density: 0.85 to 1.00 g/cc
Rock fragments: 15 to 35 percent; 0 to 5 percent cobbles, 15 to 30 percent pebbles
Reaction: pH 5.6 to 6.5
Bw1 horizon - Value: 5 or 6 dry, 3 or 4 moist
Chroma: 3, 4 or 6
Clay content: 2 to 10 percent
Volcanic glass content in the 0.02 to 2.0 mm fraction: 12 to 20 percent
Acid-oxalate extractable Al plus 1/2 Fe: 1.60 to 2.25
Phosphate retention: 25 to 75 percent
15-bar water retention on air dried samples: 8 to 12 percent
Bulk density: 0.85 to 1.00 g/cc
Rock fragments: 15 to 35 percent--10 to 15 percent cobbles, 5 to 20 percent pebbles
Reaction: pH 5.6 to 6.5
Bw2 horizon - Value: 6 or 7 dry, 4 or 5 moist
Chroma: 3, 4 or 6
Clay content: 2 to 10 percent
Volcanic glass content in the 0.02 to 2.0 mm fraction: 12 to 20 percent
Acid-oxalate extractable Al plus 1/2 Fe: 1.60 to 2.25
Phosphate retention: 25 to 75 percent
15-bar water retention on air dried samples: 8 to 12 percent
Bulk density: 0.85 to 1.00 g/cc
Rock fragments: 15 to 35 percent--10 to 20 percent cobbles, 5 to 15 percent pebbles
Reaction: pH 5.6 to 6.5
2E horizon - Value: 7 or 8 dry; 5 or 6 moist
Chroma: 2 or 3
Texture: loam, silt loam, or fine sandy loam
Clay content: 12 to 20 percent
Rock fragments: 35 to 60 percent--trace stones, 20 to 30 percent cobbles, 15 to 30 percent pebbles
Reaction: pH 5.1 to 6.0
2Bt/E horizon - Value: B part - 6 or 7 dry; 4 or 5 moist E part: 7 or 8 dry; 5 or 6 moist
Chroma: B part: 4 or 6, E part: 2 or 3
Texture: loam, clay loam or sandy clay loam
Clay content: 18 to 27 percent
Rock fragments: 35 to 60 percent--0 to 5 percent stones, 20 to 30 percent cobbles, 15 to 25 percent pebbles
Reaction: pH 5.1 to 6.0
2Bt horizon - Value: 6 or 7 dry; 4 or 5 moist
Chroma: 4 or 6
Texture: loam, clay loam or sandy clay loam
Clay content: 20 to 35 percent
Rock fragments: 35 to 60 percent--0 to 5 percent stones, 20 to 35 percent cobbles, 15 to 20 percent pebbles
Reaction: pH 5.1 to 6.0
COMPETING SERIES:
Limberjim (OR) - has a lithic contact of basalt t 40 to 60 inches.
Syrupcreek (OR) - has a lithic contact of basalt at 20 to 40 inches.
GEOGRAPHIC SETTING:
Landform - ground moraines and mountains.
Elevation - 2,200 to 3,000 feet.
Slope - 4 to 35 percent.
Parent material - glacial till with a mantle of volcanic ash.
Climate - long, cold winters; moist springs, warm summers.
Mean annual precipitation - 28 to 34 inches, much of which falls as snow and spring rains.
Mean annual temperature - 42 to 45 degrees F.
Frost-free period - 70 to 90 days.
DRAINAGE AND PERMEABILITY: Well drained, moderately slow permeability.
USE AND VEGETATION: Courvash soils are used mainly for woodland, understory grazing, and wildlife habitat. Potential native vegetation is mainly western larch, Douglas-fir, grand fir, lodgepole pine, Engelmann spruce, western hemlock, and western redcedar. Understory vegetation is mainly twinflower, queencup beadlily, pachistima, arnica, blue huckleberry, western goldthread, oregon grape, snowberry, wild sarsaparilla and other forbs and shrubs.
DISTRIBUTION AND EXTENT: Courvash soils are of small extent in the valleys of northwestern Montana.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana.
SERIES ESTABLISHED: Sanders County, Montana 1997.
REMARKS: Soil Interpretation Record: MT1511. Diagnostic horizons and features recognized in this pedon are: a volcanic ash mantle from the mineral soil surface to 18 inches (A, Bw1 and Bw2 horizons); an ochric epipedon from the mineral soil surface to 7 inches (A, Bw1 horizons); an albic horizon from 18 to 31 inches (2E horizon); an argillic horizon from 31 to 60 inches (2Bt/E, 2Bt horizons); a particle size control section from 0 to 40 inches below the mineral soil surface (A, Bw1, Bw2, 2E, and 2Bt/E horizons). Courvash soils have a udic moisture regime and a frigid temperature regime.
ADDITIONAL DATA: Lab data S94MT-089-003