LOCATION OVERFELT MTEstablished Series
TAXONOMIC CLASS: Clayey over loamy-skeletal, smectitic over mixed, superactive, frigid Vertic Argiustolls
TYPICAL PEDON: Overfelt gravelly loam, grassland (colors are for dry soil unless otherwise noted).
A--0 to 8 inches; brown (7.5YR 4/2) clay loam, dark brown (7.5YR 3/2) moist; weak fine subangular blocky structure parting to moderate fine granular; slightly hard, friable, slightly sticky and slightly plastic; common fine and few medium roots; many very fine and fine pores; 2 percent pebbles, 3 percent cobbles; neutral (pH 7.0); abrupt smooth boundary. (5 to 12 inches thick)
Bt1--8 to 16 inches; brown (7.5YR 5/2) clay, dark brown (7.5YR 4/2) moist; moderate medium prismatic structure parting to strong medium subangular blocky; very hard, firm, very sticky and very plastic; common fine roots; common fine and very fine pores; common pressure faces and cracks 1/4 to 1/2 inches wide; continuous distinct clay films in pores and on faces of peds; 5 percent pebbles; neutral (pH 7.2); clear smooth boundary.
Bt2--16 to 27 inches; brown (7.5YR 5/2) clay, dark brown (7.5YR 4/2) moist; moderate medium prismatic structure parting to strong medium subangular blocky; very hard, firm, very sticky and very plastic; common fine roots; common fine and very fine pores; common pressure faces and cracks 1/4 to 1/2 inches wide; continuous distinct clay films in pores and on faces of peds; 5 percent pebbles; slightly alkaline (pH 7.4); clear smooth boundary. (Combined thickness of Bt horizon is 15 to 24 inches)
2Bk1--27 to 42 inches; brown (10YR 5/3) very gravelly sandy clay loam, dark brown (10YR 4/3) moist; weak coarse prismatic structure; slightly hard, very friable, slightly sticky and slightly plastic; few very fine and fine roots; common fine and medium pores; 35 percent pebbles; 15 percent cobbles; 5 percent stones; many distinct carbonate coats on lower surfaces of coarse fragments; strongly effervescent; moderately alkaline (pH 8.4); gradual smooth boundary. (10 to 24 inches thick)
3Bk2--42 to 61 inches; pale brown (10YR 6/3) very gravelly coarse sand, brown (10YR 5/3) moist; single grain; loose, nonsticky and nonplastic; 35 percent pebbles, 15 percent cobbles, 5 percent stones; few faint carbonate coats on lower surfaces of coarse fragments; strongly effervescent; moderately alkaline (pH 8.4).
TYPE LOCATION: Sweet Grass County, Montana; 2400 feet east and 2000 feet north of the southwest corner of section 8, T.1 S., R.16 E.; Latitude - 45 degrees, 45 minutes, 33 seconds North; Longitude - 109 degrees, 46 minutes, 41 seconds West.
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.
Depth to Bk horizon - 20 to 36 inches.
Depth to 3Bk horizon - 40 to over 60 inches.
A horizon - Hue: 7.5YR or 10YR
Value: 4 or 5 dry; 2 or 3 moist
Chroma: 2 or 3
Texture: clay loam, loam or silty clay loam
Clay content: 20 to 40 percent
Rock fragments: 0 to 25 percent--0 to 5 percent cobbles, 0 to 20 percent pebbles
Reaction: pH 6.6 to 7.8
Bt horizons - Hue: 7.5YR or 10YR
Value: 5 or 6 dry; 4 or 5 moist
Chroma: 2, 3, or 4
Texture: clay or silty clay
Clay content: 50 to 70 percent
Rock fragments: 0 to 15 percent--0 to 5 percent cobbles, 0 to 10 percent pebbles
Reaction: pH 6.6 to 7.8
2Bk1 horizon - Hue: 7.5YR or 10YR
Value: 5, 6, or 7 dry; 4, 5, or 6 moist
Chroma: 2, 3, or 4
Texture: sandy clay loam, clay loam, loam or sandy loam
Clay content: 15 to 35 percent
Rock fragments: 35 to 70 percent--0 to 5 percent stones; 5 to 20 percent cobbles, 30 to 45 percent pebbles
Calcium carbonate equivalent: 5 to 15 percent
Reaction: pH 7.4 to 8.4
3Bk2 horizon - Hue: 7.5YR, 10YR, or 2.5Y
Value: 5, 6, or 7 dry; 4, 5, or 6 moist
Chroma: 2, 3, or 4
Texture: coarse sand, sand, loamy sand or loamy coarse sand
Clay content: 1 to 10 percent
Rock fragments: 35 to 80 percent--0 to 10 percent stones, 5 to 25 percent cobbles, 30 to 45 percent pebbles
Calcium carbonate equivalent: 1 to 10 percent
Reaction: pH 7.4 to 8.4
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING:
Landform - alluvial fans and stream terraces
Elevation - 3,400 to 6,000 feet.
Slope- 0 to 8 percent.
Parent material - alluvium
Climate - long, cold winters; moist springs; warm summers.
Mean annual precipitation - 14 to 19 inches.
Mean annual air temperature - 39 to 45 degrees F.
Frost-free period - 85 to 125 days.
DRAINAGE AND PERMEABILITY: Well drained; very slow permeability above the loamy-skeletal material and moderate in the loamy-skeletal material.
USE AND VEGETATION: Overfelt soils are used mainly for native grassland. Potential native vegetation is mainly bluebunch wheatgrass, bluegrass, and prairie junegrass.
DISTRIBUTION AND EXTENT: Overfelt soils are of minor extent in south central Montana.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Sweet Grass County, Montana, 1999.
REMARKS: Diagnostic horizons and features recognized in this pedon are: a mollic epipedon from the soil surface to 8 inches (A horizon); an argillic horizon from 8 to 27 inches (Bt horizons); horizons of calcium carbonate accumulation from 27 to 61 inches (2Bk1, 3Bk2 horizons); a lithologic discontinuity at 27 inches (2Bk1 horizon); and a particle-size control section from 8 to 40 inches (Bt1, Bt2, 2Bk1 horizons). Overfelt soils have an ustic moisture regime and a frigid temperature regime.
ADDITIONAL DATA: NSSL Pedon 91P 259, Samples 91P1579-1583.