LOCATION BIGDRAW MTEstablished Series
TAXONOMIC CLASS: Fine-loamy, mixed, active, frigid Typic Argixerolls
TYPICAL PEDON: Bigdraw gravelly loam, rangeland (colors are for dry soil unless otherwise noted).
A1--0 to 3 inches; dark grayish brown (10YR 4/2) gravelly loam, very dark brown (10YR 2/2) moist; moderate fine granular structure; soft, very friable, slightly sticky and slightly plastic; many very fine and fine, and few medium roots; 25 percent gravel; neutral (pH 6.8); clear smooth boundary.
A2--3 to 9 inches; dark grayish brown (10YR 4/2) gravelly loam, very dark brown (10YR 2/2) moist; weak medium subangular blocky structure; soft, very friable, slightly sticky and slightly plastic; many very fine, fine, and few medium roots; common very fine tubular pores; 25 percent gravel; slightly acid (pH 6.4); clear smooth boundary. (Combined thickness of the A horizons is 7 to 16 inches.)
Bt1--9 to 15 inches; pale brown (10YR 6/3) gravelly clay loam, brown (10YR 4/3) moist; moderate fine and medium angular blocky structure; slightly hard, friable, sticky and plastic; common very fine, fine, and few medium roots; common very fine and fine tubular pores; common prominent clay films on ped faces and in pores; 15 percent gravel, 5 percent cobbles; neutral (pH 7.2); clear smooth boundary. (5 to 12 inches thick)
Bt2--15 to 20 inches; light yellowish brown (10YR 6/4) gravelly loam, dark yellowish brown (10YR 4/4) moist; strong fine and medium subangular blocky structure; slightly hard, friable, sticky and plastic; common fine roots; common very fine and fine tubular pores; few faint clay films on ped faces; 15 percent gravel, 20 percent paragravel; slightly effervescent, slightly alkaline (pH 7.4); clear smooth boundary. (0 to 8 inches thick)
Bk--20 to 28 inches; very pale brown (10YR 7/3) very paragravelly coarse sandy loam, pale brown (10YR 6/3) moist; massive; soft, very friable, slightly sticky and nonplastic; few fine roots; 10 percent gravel, 45 percent paragravel; strongly effervescent, common seams and soft masses of lime; moderately alkaline (pH 8.2); gradual smooth boundary. (3 to 12 inches thick)
Cr--28 inches; semiconsolidated welded tuff.
TYPE LOCATION: Sanders County, Montana; 1,650 feet south and 200 feet west of the northeast corner of Sec. 35, T. 25 N., R. 23 W.
RANGE IN CHARACTERISTICS:
Soil temperature - 41 to 45 degrees F.
Moisture control section - between 4 and 12 inches.
Mollic epipedon thickness - 7 to 16 inches.
Control section - 20 to 35 percent clay.
Rock fragments - 10 to 35 percent hard fragments.
Depth to Cr horizon - 20 to 40 inches.
Depth to lime - 12 to 28 inches (the lime in this series is believed to be contamination from Glacial Lake Missoula).
Soil phases - HIGH PPT--this phase generally has lower concentrations of lime.
A horizons - Value: 4 or 5 dry, 2 or 3 moist
Chroma: 1 or 2
Clay content: 10 to 27
Rock fragments: 15 to 50 percent--15 to 30 percent gravel, 0 to 5 percent cobbles, 0 to 15 percent paragravel
Reaction: pH 6.1 to 7.3
Bt1 horizon - Hue: 10YR, 2.5Y
Value: 5 or 6 dry, 4 moist
Chroma: 3, 4, or 6
Texture: sandy clay loam, clay loam
Clay content: 20 to 35 percent
Rock fragments: 10 to 70 percent--10 to 30 percent gravel, 0 to 5 percent hard cobbles, 0 to 35 percent paragravel
Reaction: pH 6.1 to 7.3
Bt2 horizon - Hue: 10YR, 2.5Y
Value: 5 or 6 dry, 4 moist
Chroma: 3, 4, or 6
Texture: clay loam, loam
Clay content: 20 to 35 percent
Rock fragments: 10 to 70 percent--10 to 30 percent gravel, 0 to 5 percent hard cobbles, 0 to 35 percent paragravel
Reaction: pH 7.4 to 7.8
Bk horizon - Hue: 10YR, 2.5Y, 7.5YR
Value: 6 or 7 dry; 4, 5, or 6 moist
Chroma: 3, 4, or 6
Texture: coarse sandy loam, sandy loam
Clay content: 10 to 18
Rock fragments: 35 to 60 percent--10 to 15 percent gravel, 25 to 45 percent paragravel
Calcium carbonate equivalent: 3 to 10 percent
Reaction: pH 7.8 to 8.4
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING:
Landform- hills.
Slope - 4 to 50 percent.
Elevation - 2,600 to 4,400 feet.
Parent material - colluvium and residuum derived from semiconsolidated welded tuff.
Climate - cold winters; moist springs; and hot, dry summers.
Mean annual precipitation - 15 to 22 inches, most of which falls as rain or snow in late fall through late spring.
Mean annual temperature - 39 to 46 degrees F.
Frost-free period - 75 to 120 days.
GEOGRAPHICALLY ASSOCIATED SOILS:
DRAINAGE AND PERMEABILITY: Well drained; moderately slow permeability.
USE AND VEGETATION: Bigdraw soils are used for rangeland, pasture, and woodland. Rangeland vegetation is mainly short and mid grasses with woodland areas dominated by a ponderosa pine overstory and a bunchgrass understory.
DISTRIBUTION AND EXTENT: Bigdraw soils are of limited extent in the north end of Hotsprings Valley of northwestern Montana. MLRA 43A.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana.
SERIES ESTABLISHED: Sanders County, Montana, 1997.
REMARKS: Soil interpretations record: MT1217. Diagnostic horizons and features recognized in this pedon are: a mollic epipedon from the soil surface to 9 inches (A1 and A2 horizons); an argillic horizon from 9 to 20 inches (Bt1 and Bt2 horizons); a paralithic contact at a depth of 28 inches; a layer with lime accumulation from 20 to 28 inches (Bk horizon); a particle size control section from 9 to 20 inches (Bt1 and Bt2 horizons). Bigdraw soils have a frigid temperature regime and a xeric moisture regime.
ADDITIONAL DATA: Laboratory data--S88MT-089-007.