LOCATION BIGBEAR MTEstablished Series
TAXONOMIC CLASS: Fine, mixed, superactive, frigid Typic Argiustolls
TYPICAL PEDON: Bigbear loam, in hayland (Colors are for dry soil unless otherwise noted).
A--0 to 9 inches; dark gray (10YR 4/1) loam, black (10YR 2/1) moist; weak medium subangular blocky structure parting to strong fine granular; slightly hard, friable, slightly sticky and slightly plastic; common very fine and fine and few medium roots; 5 percent pebbles, 5 percent cobbles; neutral (pH 6.8); clear smooth boundary. (6 to 12 inches thick)
Bt1--9 to 13 inches; grayish brown (10YR 5/2) clay loam, very dark grayish brown (10YR 3/2) moist; moderate medium subangular blocky structure parting to strong fine granular; slightly hard, firm, sticky and plastic; common very fine and few fine and medium roots; common distinct clay films on faces of peds and lining pores; 5 percent pebbles, 5 percent cobbles; neutral (pH 6.8); clear smooth boundary.
Bt2--13 to 35 inches; yellowish brown (10YR 5/4) gravelly clay, dark yellowish brown (10YR 4/4) moist; moderate medium prismatic structure parting to strong medium subangular blocky; very hard, very firm, sticky and very plastic; few very fine roots; many prominent clay films on faces of peds and lining pores; 10 percent pebbles, 5 percent cobbles; neutral (pH 7.0); clear smooth boundary. (Combined thickness of Bt horizons is 14 to 28 inches).
Bk--35 to 60 inches; yellowish brown (10YR 5/6) very cobbly sandy clay loam, dark yellowish brown (10YR 4/6) moist; weak medium subangular blocky structure; slightly hard, friable, sticky and plastic; 15 percent pebbles, 20 percent cobbles, 5 percent stones; common large masses of lime; violently effervescent; slightly alkaline (pH 7.8).
TYPE LOCATION: Gallatin County, Montana; 800 feet south and 2500 feet west of the northeast corner of sec 4, T 3S., R.6E.
RANGE IN CHARACTERISTICS:
Mean annual soil temperature - 39 to 43 degrees F.
Moisture control section - between 4 and 12 inches.
Mollic epipedon thickness - 8 to 15 inches.
Depth to calcic horizon - 20 to 40 inches.
Soil phases: stony.
A horizon - Value: 3 or 4 dry; 2 or 3 moist
Texture: loam or clay loam
Clay content: 18 to 35 percent
Rock fragments: 5 to 35 percent--0 to 15 percent pebbles, 5 to 15 percent cobbles, 0 to 5 percent stones
Reaction: pH 6.6 to 7.8
Bt1 horizon - Value: 4 or 5 dry; 3 or 4 moist
Chroma: 2, 3 or 4
Texture: clay loam or clay
Clay content: 35 to 50 percent
Rock fragments: 5 to 30 percent-- 5 to 20 percent pebbles, 0 to 10 percent cobbles
Reaction: pH 6.6 to 7.8
Bt2 horizon - Value: 4 or 5 dry; 3 or 4 moist
Chroma: 3 or 4
Texture: clay loam or clay
Clay content: 35 to 50 percent
Rock fragments: 5 to 30 percent-- 5 to 20 percent pebbles,
0 to 10 percent cobbles
Reaction: pH 6.6 to 7.8
Bk horizon - Value: 5, 6 or 7 dry; 3, 4 or 5 moist
Chroma: 3, 4, 5 or 6
Texture: clay loam, sandy clay loam or loam
Clay content: 25 to 40 percent
Rock fragments: 15 to 45 percent-- 10 to 25 percent pebbles, 5 to 20 percent cobbles, 0 to 5 percent stones
Calcium carbonate equivalent: 15 to 30
Reaction: pH 7.4 to 8.4
COMPETING SERIES:
Alder (MT) - has a paralithic contact at 20 to 40 inches.
Durston (MT) - has less than 15 percent coarse fragments in the Bk horizon; formed in loess.
GEOGRAPHIC SETTING:
Landform - relict stream terraces, hills and escarpments.
Elevation - 5,000 to 6,000 feet.
Slope- 0 to 45 percent.
Parent material - alluvium or colluvium.
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; slow permeability.
USE AND VEGETATION: Bigbear soils are used mainly for hayland, pasture and rangeland. Potential native vegetation may include subalpine needlegrasses, big bluegrass, Idaho fescue, rough and spike Fescues, mountain brome, sedges, lupine, sticky geranium and other grasses and forbs.
DISTRIBUTION AND EXTENT: Bigbear soils are of small extent in southwestern Montana.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Gallatin County, Montana, 1997.
REMARKS: Soi interpretation record: MT1444, MT1604. Diagnostic horizons and features recognized in this pedon are: a mollic epipedon from the surface to 13 inches (A, Bt1 horizons), an argillic horizon from 9 to 35 inches (Bt1, Bt2 horizon); a calcic horizon from 35 to 60 inches (Bk horizon); a particle-size control section from 9 to 29 inches (Bt1, Bt2 horizons). Bigbear soils have a frigid temperature regime and an ustic moisture regime.