LOCATION SWEETGRASS MTEstablished Series
TAXONOMIC CLASS: Clayey over sandy or sandy-skeletal, smectitic over mixed, frigid Typic Argiustolls
TYPICAL PEDON: Sweetgrass gravelly loam, grassland (colors are for dry soil unless otherwise noted).
A--0 to 7 inches; dark grayish brown (10YR 4/2) gravelly loam, very dark grayish brown (10YR 3/2) moist; weak fine granular structure; soft, very friable, slightly sticky and slightly plastic; common fine and medium roots; many fine and very fine pores; 2 percent cobbles; 15 percent pebbles; slightly alkaline (pH 7.6); abrupt smooth boundary. (4 to 8 inches thick)
Bt--7 to 13 inches; brown (10YR 5/3) clay, dark brown (10YR 4/3) moist; moderate medium subangular blocky structure parting to weak fine subangular blocky; slightly hard, friable, moderately sticky and moderately plastic; continuous distinct dark brown (7.5YR 4/2) clay films in pores and on faces of peds; few fine and medium roots; many very fine pores; 1 percent pebbles; slightly alkaline (pH 7.6); abrupt smooth boundary. (6 to 15 inches thick)
2Bk1--13 to 19 inches; light gray (10YR 7/2) sandy clay loam, pale brown (10YR 6/3) moist; weak coarse prismatic structure; slightly hard, very friable, slightly sticky and slightly plastic; few fine roots; common fine pores; 5 percent pebbles; disseminated lime; common large masses of lime; violent effervescence; moderately alkaline (pH 8.4); clear smooth boundary.
2Bk2--19 to 28 inches; white (10YR 8/3) gravelly sandy loam, light gray (10YR 7/2) moist; weak coarse prismatic structure; soft, very friable, nonsticky and nonplastic; 15 percent pebbles, 5 percent cobbles; disseminated lime; common large masses of lime; continuous distinct lime cast on all sides of coarse fragments; violent effervescence; moderately alkaline (pH 8.4); clear smooth boundary. (Combined thickness of Bk1 and Bk2 horizons is 7 to 21 inches)
3Bk33--28 to 43 inches; light gray (10YR 7/2) very gravelly loamy coarse sand, yellowish brown (10YR 5/4) moist; single grain; loose, nonsticky and nonplastic; 35 percent pebbles, 10 percent cobbles; disseminated lime; continuous distinct lime casts on underside of coarse fragments; violent effervescence; moderately alkaline (pH 8.4); gradual smooth boundary. (10 to 30 inches thick)
3C--43 to 60 inches; pale brown (10YR 6/3) extremely gravelly coarse sand; yellowish brown (10YR 5/4) moist; single grain; loose, nonsticky and nonplastic; 45 percent pebbles, 20 percent cobbles, 10 percent stones; few distinct lime casts on the underside of coarse fragments; strong effervescence; moderately alkaline (pH 8.4).
TYPE LOCATION: Sweet Grass County, Montana; 2,400 feet east and 1,450 feet south of the NW corner of sec. 27, T. 1 N., R. 14 E.
RANGE IN CHARACTERISTICS:
Soil temperature - 42 to 47 degrees F.
Moisture control section - between 4 and 12 inches.
Mollic epipedon thickness - 7 to 15 inches; may extend into Bt horizon.
Control section - 35 to 50 percent clay in the argillic horizon; 35 to 80 percent coarse fragments and 1 to 10 percent clay in the contrasting sandy-skeletal horizon.
Depth to 3Bk horizon - 20 to 40 inches.
Depth to calcic horizon - 10 to 20 inches.
A horizon - Hue: 10YR or 7.5YR
Value: 4 or 5 dry; 2 or 3 moist
Chroma: 2 or 3
Texture: loam, clay loam or clay
Clay content: 20 to 50 percent
Rock fragments: 0 to 25 percent--0 to 5 percent cobbles, 0 to 25 percent pebbles
Reaction: pH 6.6 to 7.8
Bt horizon - Hue: 10YR or 7.5YR
Value: 4, 5, or 6 dry; 3, 4, or 5 moist
Chroma: 2, 3, or 4
Texture: clay loam or clay
Clay content: 35 to 50 percent
Rock fragments: 0 to 25 percent--0 to 5 percent cobbles, 0 to 25 percent pebbles
Reaction: pH 6.6 to 7.8
2Bk horizon - Hue: 10YR or 2.5Y
Value: 5, 6, 7, or 8 dry; 4, 5, 6, or 7 moist
Chroma: 2, 3, or 4
Texture: clay loam, sandy clay loam, loam, sandy loam
Clay content: 10 to 30 percent
Rock fragments: 5 to 35 percent--0 to 10 percent cobbles, 5 to 35 percent pebbles
Calcium carbonate equivalent: 15 to 50 percent
Reaction: pH 7.4 to 8.4
3Bk horizon - Hue: 10YR or 2.5Y
Value: 5, 6, or 7 dry; 4, 5, or 6 moist
Chroma: 2, 3, or 4
Texture: loamy sand, loamy coarse sand, coarse sand, sand
Clay content: 1 to 10 percent
Rock fragments: 35 to 80 percent--0 to 15 percent stones, 5 to 25 percent cobbles, 30 to 50 percent pebbles
Calcium carbonate equivalent: 10 to 20 percent
Reaction: pH 7.4 to 8.4
3C horizon - Hue: 10YR or 2.5Y
Value: 5, 6, or 7 dry; 4, 5, or 6 moist
Chroma: 2, 3, or 4
Texture: loamy sand, loamy coarse sand, coarse sand, sand
Clay content: 1 to 10 percent
Rock fragments: 35 to 80 percent--0 to 15 percent stones, 5 to 25 percent cobbles; 30 to 50 percent pebbles
Calcium carbonate equivalent: 5 to 10 percent
Reaction: pH 7.4 to 8.4
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING:
Landform - plains, alluvial fans, stream terraces, relict stream terraces.
Elevation - 3,400 to 6,000 feet.
Slope - 0 to 15 percent.
Parent material - alluvium derived as outwash from the mountains or from major streams.
Climate - long, cold winters; moist springs; warm summers.
Mean annual precipitation - 14 to 19 inches.
Mean annual air temperature - 39 to 45 degreed F.
Frost-free period - 70 to 130 days.
DRAINAGE AND PERMEABILITY: Well drained; moderately slow permeability above the sandy-skeletal material and rapid in the sandy-skeletal material.
USE AND VEGETATION: Sweetgrass soils are used mainly for native grassland. Potential native vegetation is mainly Idaho fescue, bluebunch wheatgrass, bluegrass, prairie junegrass.
DISTRIBUTION AND EXTENT: Sweetgrass soils are moderately extensive along the mountain front in central Montana.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana.
SERIES ESTABLISHED: Chouteau County, Montana, 1992.
REMARKS: Soil interpretations record: MT0436. Diagnostic horizons and features recognized in this pedon are: a mollic epipedon from the soil surface to 7 inches (A horizon); an argillic horizon from 7 to 13 inches (Bt horizon); a calcic horizon from 13 to 28 inches (2Bk1, 2Bk2 horizons); and a particle-size control section from 7 to 40 inches (Bt, 2Bk1, 2Bk2, 2Bk3 horizons). Sweetgrass soils have an ustic moisture regime and a frigid temperature regime.
ADDITIONAL DATA: Laboratory sample S89MT-097-001.