LOCATION SOURDOUGH MTEstablished Series
TAXONOMIC CLASS: Fine-loamy over sandy or sandy-skeletal, mixed, superactive, frigid Typic Argiustolls
TYPICAL PEDON: Sourdough loam, in hayland (colors are for dry soil unless otherwise noted).
A--0 to 8 inches; very dark grayish brown (10YR 3/2) loam, very dark gray (10YR 3/1) moist; moderate fine granular structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine, common fine and few medium roots; 5 percent pebbles, 5 percent cobbles; neutral (pH 7.0); clear smooth boundary. (7 to 12 inches thick)
AB--8 to 12 inches; very dark grayish brown (10YR 3/2) silt loam, very dark gray (10YR 3/1) moist; moderate medium subangular blocky structure parting to moderate fine granular; slightly hard, friable, slightly sticky and slightly plastic; many very fine and common fine and medium roots; 5 percent pebbles, 5 percent cobbles; neutral (pH 7.0); clear smooth boundary. (0 to 6 inches thick)
Bt1--12 to 15 inches; dark grayish brown (10YR 4/2) silty clay loam, very dark grayish brown (10YR 3/2) moist; moderate medium subangular blocky structure; hard, friable, moderately sticky and slightly plastic; many very fine, common fine and few medium roots; common faint clay films on faces of peds and lining pores; 5 percent pebbles and 5 percent cobbles; neutral (pH 7.2); clear smooth boundary.
Bt2--15 to 26 inches; brown (10YR 5/3) silty clay loam, dark brown (10YR 4/3) moist; weak medium prismatic structure parting to moderate medium subangular blocky; hard, friable, moderately sticky and moderately plastic; common very fine and fine and few medium roots; common distinct clay films on faces of peds and lining pores; 5 percent pebbles and 5 percent cobbles; neutral (pH 7.3); clear wavy boundary.
Bt3--26 to 36 inches; brown (10YR 5/3) cobbly silty clay loam, dark grayish brown (10YR 4/2) moist; moderate medium subangular blocky structure; hard, friable, moderately sticky and moderately plastic; common very fine and fine, few medium and coarse roots; common faint clay films on faces of peds and lining pores; 10 percent pebbles and 10 percent cobbles; neutral (pH 7.2); clear wavy boundary. (Combined thickness of Bt horizons is 13 to 28 inches).
2C--36 to 60 inches; brown (10YR 5/3) extremely cobbly loamy coarse sand, dark brown (10YR 3/3) moist; massive; loose, nonsticky and nonplastic; common very fine and few fine roots; 30 percent pebbles, 35 percent cobbles, 5 percent stones; common distinct lime coatings on undersides of coarse fragments; slightly alkaline (pH 7.6).
TYPE LOCATION: Gallatin Montana, 200 feet south and 500 feet west of the northeast corner of sec.10, T.3S., R.5E.
RANGE IN CHARACTERISTICS:
Soil temperature - 39 to 43 degrees F.
Moisture control section - between 4 and 12 inches; not dry in all parts for 45 consecutive days.
Mollic epipedon thickness - 10 to 15 inches and includes all or part of the argillic horizon.
Depth to 2C horizon - 20 to 40 inches.
A horizon - Value: 3 or 4 dry; 2 or 3 moist
Clay content: 18 to 27 percent
Rock fragments: 0 to 15 percent--0 to 10 percent pebbles,
0 to 5 percent cobbles
Reaction: pH 6.1 to 7.3
AB horizon - Value: 3 or 4 dry; 2 or 3 moist
Chroma: 1 or 2
Texture: silty clay loam, loam, silt loam
Clay content: 18 to 30 percent
Rock fragments: 0 to 15 percent-- 0 to 10 percent pebbles, 0 to 5 percent cobbles
Reaction: pH 6.1 to 7.3
Bt1, Bt2 horizons - Value: 4 or 5 dry; 3 or 4 moist
Chroma: 2 to 4
Texture: clay loam, silty clay loam
Clay content: 27 to 35 percent
Rock fragments: 0 to 15 percent-- 0 to 10 percent pebbles,
0 to 5 percent cobbles
Reaction: pH 6.6 to 7.3
Bt3 horizon - Value: 4 or 5 dry; 3 or 4 moist
Chroma: 2 to 4
Texture: silty clay loam, clay loam, silt loam
Clay content: 25 to 35 percent
Rock fragments: 10 to 30 percent--5 to 15 percent pebbles, 5 to 15 percent cobbles
Reaction: pH 6.6 to 7.3
2C horizon - Value: 5 or 6 dry; 3 or 4 moist
Chroma: 2 to 4
Texture: loamy coarse sand, coarse sand
Clay content: 0 to 10 percent
Rock fragments: 40 to 80 percent-- 20 to 50 percent pebbles
20 to 40 percent cobbles, 5 to 10 percent stones
Reaction: pH 6.6 to 7.8
COMPETING SERIES:
Buckcamp (UT) - has a lithic contact at 40 to 60 inches; has horizons of secondary carbonate accuulation.
Hedstrom (MT) - has horizons of secondary carbonate accumulation.
Turner (MT) - has horizons of secondary carbonate accumulation.
GEOGRAPHIC SETTING:
Landform - alluvial fans and stream terraces
Elevation - 5000 to 5500 feet.
Slope - 0 to 4 percent.
Parent material - alluvium.
Climate - long cold winters, moist springs, warm summers.
Mean annual precipitation - 18 to 22 inches.
Mean annual air temperature - 37 to 41 degrees F.
Frost-free period - 80 to 95 days.
DRAINAGE AND PERMEABILITY: Well drained; moderately slow permeability.
USE AND VEGETATION: Sourdough soils are used mainly for cropland. Potential native vegetation is mainly Idaho fescue, bluebunch wheatgrass, Columbia needlegrass, mountain brome, lupine, sticky geranium, and wild rose.
DISTRIBUTION AND EXTENT: Sourdough soils are of small extent in southwestern Montana.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Gallatin County, Montana, 1997.
REMARKS: Soil interpretation record: MT1625. Diagnostic horizons and features recognized in this pedon are: a mollic epipedon from the surface to 15 inches (A, AB,Bt1 horizons); an argillic horizon from 12 to 36 inches (Bt1, Bt2, Bt3 horizons); a litholgic discontinuity at 36 inches (2C horizon), a particle size control section from 12 to 32 inches (Bt1, Bt2, Bt3 horizons). Sourdough soils have a frigid temperature regime and an ustic moisture regime bordering on udic.