LOCATION COBEN MT
Established Series
Rev. HAL-JAL
01/2023
COBEN SERIES
The Coben series consists of very deep, well drained soil that formed in alluvium. These soils are on alluvial fans and stream terraces. Slopes are 0 to 35 percent. Mean annual precipitation is about 16 inches, and mean annual temperature is about 41 degrees F.
TAXONOMIC CLASS: Fine, smectitic, frigid Vertic Argiustolls
TYPICAL PEDON: Coben clay loam, grassland (colors are for dry soil unless otherwise noted).
A--0 to 5 inches; grayish brown (10YR 5/2) clay loam, very dark grayish brown (10YR 3/2) moist; weak medium platy structure parting to weak fine granular; slightly hard, friable, moderately sticky and moderately plastic; many very fine roots; many fine and very fine irregular pores; 5 percent pebbles; neutral (pH 6.8); abrupt wavy boundary. (4 to 8 inches thick)
Bt--5 to 12 inches; grayish brown (10YR 5/2) clay, very dark grayish brown (10YR 3/2) moist; strong medium columnar structure parting to strong medium blocks; very hard, very firm, very sticky and very plastic; common very fine roots between ped faces; few fine tubular pores; many distinct clay films on faces of peds; neutral (pH 7.1); gradual smooth boundary. (6 to 23 inches thick)
Bk1--12 to 24 inches; pale brown (10YR 6/3) clay, dark brown (10YR 4/3) moist; weak medium subangular blocky structure; hard, firm, very sticky and very plastic; common very fine roots between peds; few fine tubular pores; few faint clay films on faces of peds; few fine masses of lime; strongly effervescent; slightly alkaline (pH 7.6); gradual smooth boundary.
Bk2--24 to 40 inches; pale brown (10YR 6/3) clay, yellowish brown (10YR 5/4) moist; weak coarse subangular blocky structure; hard, firm, very sticky and very plastic; few very fine roots; few fine tubular pores; very few faint clay films along root channels; few fine masses of lime; strongly effervescent; moderately alkaline (pH 8.1); gradual wavy boundary. (Combined thickness of the Bk horizons is 10 to 40 inches thick)
By--40 to 46 inches; pale brown (10YR 6/3) clay, yellowish brown (10YR 5/4) moist; massive; hard, firm, very sticky and very plastic; few very fine roots; many very fine pores; many very fine white gypsum nodules; strongly effervescent; moderately alkaline (pH 8.2); gradual wavy boundary. (0 to 15 inches thick)
BC--46 to 60 inches; brown (10YR 5/3) clay loam, dark yellowish brown (10YR 4/4) moist; massive; hard, friable, moderately sticky and very plastic; slightly effervescent; moderately alkaline (pH 7.9). (0 to 15 inches thick)
TYPE LOCATION: Granite County, Montana; about 2,600 feet west and 25 feet south of the NE corner of sec. 32, T. 10 N., R. 12 W.
RANGE IN CHARACTERISTICS:
Soil temperature - 38 to 43 degrees F.
Moisture control section - 4 to 12 inches.
Mollic epipedon thickness - 7 to 15 inches.
Depth to lime - 12 to 30 inches.
Depth to Bt horizon - 4 to 7 inches.
Depth to By horizon - 40 to 60 inches.
A horizon - Hue: 10YR or 2.5Y
Value: 4 or 5 dry; 2 or 3 moist
Chroma: 2 or 3
Texture: loam or clay loam
Clay content: 20 to 35 percent
Rock fragments: 0 to 15 percent pebbles
Reaction: pH 6.1 to 7.3
Bt horizon - Hue: 10YR or 2.5Y
Value: 4 or 5 dry; 3 or 4 moist
Chroma: 2, 3, or 4
Texture: clay, silty clay, or clay loam
Clay content: 35 to 60 percent
Rock fragments: 0 to 10 percent
Sodium absorption ratio: 0 to 8 percent
Reaction: pH 6.6 to 8.4
Bk1 horizon - Hue: 10YR or 2.5Y
Value: 5 or 6 dry; 4 or 5 moist
Chroma: 3 or 4
Texture: clay, clay loam, or silty clay loam
Clay content: 30 to 50 percent
Rock fragments: 0 to 10 percent pebbles
Calcium carbonate equivalent: 5 to 15 percent
Reaction: pH 7.4 to 8.4
Bk2 horizon - Hue: 10YR
Value: 6 or 7 dry; 4 or 5 moist
Chroma: 3 or 4
Texture: clay or clay loam
Clay content: 30 to 45 percent
Rock fragments: 0 to 10 percent
Calcium carbonate equivalent: 5 to 15 percent
Reaction: pH 7.4 to 8.4
By horizon - Hue: 10YR
Value: 6 or 7 dry; 4 or 5 moist
Chroma: 3 or 4
Texture: clay or clay loam
Rock fragments: 0 to 10 percent
Clay content: 30 to 45 percent
Calcium carbonate equivalent: 5 to 10 percent
Gypsum: 0 to 2 percent
Reaction: pH 7.4 to 8.4
BC horizon - Hue: 10YR
Value: 5, 6, or 7 dry; 4 or 5 moist
Chroma: 3 or 4
Texture: clay loam or loam
Clay content: 20 to 35 percent
Rock fragments: 5 to 35 percent pebbles
Reaction: pH 7.4 to 8.4
COMPETING SERIES:
Bearpaw (MT) - has till at 30 to 40 inches.
Burnel (MT) - is pachic.
Cedarsprings (NM) - does not have horizons of secondary carbonate accumulation.
Cerro (CO) - has stones in the Bt and Bk horizons.
Danvers (MT) - has calcic horizons.
Fergus (MT) - has hues of 7.5YR or redder in the lower Bt horizon and below.
Gerber (MT) - has a lithologic discontinuity of till.
Grail (ND) - is pachic.
Mondamin (SD) - has redox features at 24 to 40 inches; formed in glaciolacustrine sediments.
Montillo (NM) - has a lithic contact of basalt at 20 to 40 inches; does not have horizons of secondary carbonate accumulation.
Pagoda (CO) - is pachic.
Regent (ND) - has a paralithic contact at 20 to 40 inches.
Reget (WY) - has a paralithic contact at 20 to 40 inches.
Ridgeview (SD) - has tongues of darker material in the argillic horizons.
Wyola (MT) - has soil temperature of 42 to 47 degrees F.
Suposo (NM) - is pachic.
Tomasaki(UT) - does not have horizons of secondary carbonate accumulation.
Tsoodzil (NM) - does not have horizons of secondary carbonate accumulation.
Yankee (NM) - is pachic.
GEOGRAPHIC SETTING:
Landform - alluvial fans; stream terraces.
Elevation - 3,500 to 5,800 feet.
Slope - 0 to 35 percent.
Parent material - alluvium.
Climate - long, cold winters; moist springs; warm summers.
Mean annual precipitation - 15 to 19 inches.
Mean annual air temperature - 38 to 44 degrees F.
Frost-free period - 70 to 90 days.
GEOGRAPHICALLY ASSOCIATED SOILS: None listed.
DRAINAGE AND PERMEABILITY: Well drained; slow permeability.
USE AND VEGETATION: Coben soils are used mainly for dryland and irrigated crops, and rangeland. Potential native vegetation is mainly western wheatgrass, thickspike wheatgrass, blue grama, Sandberg bluegrass, Idaho fescue, grasses, and forbs.
DISTRIBUTION AND EXTENT: Coben soils are of moderate extent in the foothills and mountain valleys of western Montana. MLRA 44.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Granite County (Philipsburg-Drummond Area), Montana, 1970.
REMARKS: Soil interpretations record: MT0519. Diagnostic horizons and features recognized in this pedon are: a mollic epipedon from the soil surface to 12 inches (A, Bt horizons); an argillic horizon from 5 to 12 inches (Bt horizon); accumulation of lime from 12 to 40 inches (Bk1, Bk2 horizons); accumulation of gypsum from 40 to 46 inches (By horizon); a particle-size control section from 5 to 12 inches (Bt horizon). Coben soils have a frigid temperature regime and an ustic moisture regime.
National Cooperative Soil Survey
U.S.A.