LOCATION COMBEST MTEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, frigid Andic Haplustepts
TYPICAL PEDON: Combest gravelly ashy silt loam, forested (colors are for dry soil unless otherwise noted).
Oi--0 to 2 inches; undecomposed and slightly decomposed forest litter.
A--2 to 4 inches; very dark grayish brown (10YR 3/2) gravelly ashy silt loam, very dark brown (10YR 2/2) moist; weak fine granular structure; soft, very friable, nonsticky and slightly plastic; many very fine, fine, medium, and coarse roots; volcanic ash component; 20 percent gravel; slightly acid (pH 6.4); clear smooth boundary. (2 to 3 inches thick)
Bw--4 to 12 inches; light yellowish brown (10YR 6/4) gravelly ashy silt loam, dark yellowish brown (10YR 4/4) moist; weak fine granular structure; soft, very friable, nonsticky and slightly plastic; many very fine, fine, medium, and coarse roots; 30 percent gravel; slightly acid (pH 6.4); abrupt wavy boundary. (8 to 10 inches thick)
2E--12 to 26 inches; light gray (10YR 7/2) very gravelly sandy loam, grayish brown (10YR 5/2) moist; weak fine subangular blocky structure; soft, very friable, nonsticky and nonplastic; common very fine and fine, few medium and coarse roots; 15 percent cobbles, 40 percent gravel; slightly acid (pH 6.2); gradual wavy boundary. (4 to 16 inches thick)
2E/Bw--26 to 60 inches; E part (80 percent) is light gray (10YR 7/2) extremely cobbly sandy loam, grayish brown (10YR 5/2) moist that surrounds the B part (20 percent) is pale brown (10YR 6/3) extremely cobbly sandy loam, brown (10YR 5/3) moist; massive; soft, very friable, nonsticky and nonplastic; few very fine, fine, and medium roots; 30 percent cobbles, 40 percent gravel; moderately acid (pH 6.0).
TYPE LOCATION: Sanders County, Montana; 1,800 feet north and 800 feet west of the SE corner of sec. 28, T. 20 N., R. 27 W.
RANGE IN CHARACTERISTICS:
Soil temperature - 44 to 47 degrees F.
Moisture control section - between 8 and 24 inches.
A horizon - Value: 3, 4, or 5 dry; 2 or 3 moist
Chroma: 2 or 3
Clay content: 5 to 15 percent
Rock fragments: 15 to 35 percent--0 to 5 percent cobbles, 15 to 30 percent gravel
Moist bulk density: 0.85 to 1.0 g/cc
Acid oxalate extraction Al + 1/2 Fe: 0.4 to 1.0 percent
Reaction: pH 5.6 to 6.5
Bw horizon - Clay content: 5 to 15 percent
Rock fragments: 15 to 35 percent--0 to 5 percent cobbles, 15 to 30 percent gravel
Acid oxalate extraction Al + 1/2 Fe: 1.0 to 1.25 percent
Moist bulk density: 0.85 to 1.0 g/cc
Reaction: pH 5.6 to 6.5
2E horizon - Value: 6 or 7 dry
Chroma: 1, 2, or 3
Texture: sandy loam or loam
Clay content: 5 to 10 percent
Rock fragments: 35 to 75 percent0 to 5 percent stones and boulders, 10 to 20 percent cobbles, 25 to 55 percent gravel
Reaction: pH 5.6 to 6.5
2E/Bw horizon - Value: E part 6 or 7, B part 5 or 6 dry; E part 5 or 6, B part 4 or 5 moist
Chroma: E part 2 or 3, B part 3 or 4
Texture: sandy loam, coarse sandy loam or loam
Clay content: 5 to 10 percent
Rock fragments: 60 to 80 percent--0 to 5 percent stones and boulders, 30 to 40 percent cobbles, 20 to 40 percent gravel
Reaction: pH 5.6 to 6.5
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING:
Landform mountain slopes.
Elevation - 2,400 to 5,400 feet.
Slope - 4 to 70 percent.
Parent material - volcanic ash over colluvium derived from argillite and quartzite.
Climate - long, cold winters; moist springs; warm summers.
Mean annul precipitation - 17 to 28 inches, much of which falls as snow and as spring rain.
Mean annual temperature - 39 to 45 degrees F.
Frost-free period - 70 to 90 days.
GEOGRAPHICALLY ASSOCIATED SOILS:
DRAINAGE AND PERMEABILITY: Somewhat excessively drained; moderately rapid permeability.
USE AND VEGETATION: Combest soils are used for timber production, wildlife habitat, and watersheds. Potential native vegetation is mainly Douglas-fir and ponderosa pine with an understory of white spirea, saskatoon serviceberry, elk sedge, and pinegrass.
DISTRIBUTION AND EXTENT: Combest soils are of small extent in western Montana. MLRA 43A.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana.
SERIES ESTABLISHED: Sanders County, Montana, 1997.
REMARKS: Soil interpretation record: MT1290. Diagnostic horizons and features recognized in this pedon are: an ochric epipedon from the mineral soil surface to 7 inches (A, Bw horizons); an ash influenced layer from 2 to 12 inches (A, Bw horizons); an albic horizon from 12 to 26 inches (2E horizon); a cambic horizon from 12 to 60 inches (2E, 2E/Bw horizons); a particle-size control section from 10 to 40 inches below the mineral soil surface (2E, 2E/Bw horizons). Combest soils have a frigid temperature regime and an ustic moisture regime.