LOCATION ARMINGTON MTEstablished Series
TAXONOMIC CLASS: Very-fine, mixed, superactive, frigid Vertic Haplustolls
TYPICAL PEDON: Armington silty clay loam, in grassland. (Colors are for dry soil unless otherwise noted.)
A--0 to 4 inches; reddish brown (5YR 4/3) silty clay loam, dark reddish brown (5YR 3/3) moist; weak thick platy structure parting to strong very fine subangular blocky; hard, firm, very sticky, very plastic; common very fine and fine roots and few medium roots; 10 percent limestone, chert, and shale pebbles; slightly alkaline (pH 7.4); gradual boundary. (4 to 6 inches thick)
Bw1--4 to 11 inches; reddish brown (5YR 4/3) clay, dark reddish brown (5YR 3/3) moist; moderate fine prismatic structure parting to strong fine and medium blocky; hard, firm, very sticky, very plastic; common very fine, fine, and medium roots; common fine and medium pores; 10 percent limestone, chert, and shale pebbles; slightly effervescent; slightly alkaline (pH 7.8); clear boundary. (6 to 10 inches thick)
Bw2--11 to 16 inches; weak red (10R 5/4) clay, red (10R 4/6) moist; very hard, firm, very sticky, very plastic; few very fine, fine, and medium roots; common fine and medium pores; 10 percent limestone, chert, and shale pebbles; slightly effervescent; slightly alkaline (pH 7.8); gradual boundary. (4 to 8 inches thick)
Bw3--16 to 33 inches; weak red (10R 5/4) clay, red (10R 4/6) moist; strong medium and coarse prismatic structure parting to strong coarse blocky; extremely hard, very firm, very sticky, very plastic; few roots between peds; few fine and medium pores; few nonintersecting slickensides; slightly effervescent; slightly alkaline (pH 7.8); gradual boundary. (10 to 25 inches thick)
BC--33 to 60 inches; red (10R 5/6) clay, red (10R 4/6) moist; massive; extremely hard, very firm, very sticky, very plastic; few roots; few fine pores; slightly effervescent; slightly alkaline (pH 7.8).
TYPE LOCATION: Big Horn County (Area), Montana; 1,980 feet north and 660 feet east of the SW corner of sec. 34, T. 4 S., R. 29 E.
RANGE IN CHARACTERISTICS:
Soil temperature: 42 to 46 degrees F.
Moisture control section: approximately between the depths of 4 and 12 inches Mollic epipedon thickness: 7 to 12 inches (includes the Bw1 horizon)
Control section: 10 to 40 inches - 60 to 75 percent clay with 0 to 10 percent coarse fragments
NOTE: Some pedons have mudstone or claystone at a depth of 40 to 60 inches. Some pedons have a Bk horizon.
Mineralogy is mixed with moderate amount of mica (illitic) type clays.
In most years this soil has cracks of 1/4 to 1 1/2 inches wide during late summer months that extend from the surface to a depth of 30 inches.
A horizon - Hue: 10R, 2.5YR, or 5YR
Value: 4 or 5 dry, 2 or 3 moist
Chroma: 2 or 3
Texture: silty clay loam, silty clay, or clay
Clay content: 35 to 60 percent
Rock fragments: 0 to 10 percent pebbles
Reaction: pH 7.4 to 7.8
Bw1 horizon - Hue: 10R, 2.5YR, or 5YR
Value: 4 or 5 dry, 2 or 3 moist
Chroma: 2 or 3
Texture: clay
Clay content: 60 to 75 percent
Rock fragments: 0 to 10 percent pebbles
Reaction: pH 7.4 to 7.8
Bw2 horizon - Hue: 10R, 2.5YR, or 5YR
Value: 4 or 5 dry, 3 or 4 moist
Chroma: 4 or 6
Texture: clay
Clay content: 60 to 75 percent
Rock fragments: 0 to 10 percent pebbles
Reaction: pH 7.4 to 7.8
Bw3 horizon - Hue: 10R, 2.5YR, or 5YR
Value: 4 or 5 dry, 3 or 4 moist
Chroma: 4 or 6
Texture: clay
Clay content: 60 to 75 percent
Rock fragments: 0 to 10 percent pebbles
Reaction: pH 7.4 to 7.8
NOTE: Some pedons have a Bk horizon.
BC horizon - Hue: 10R, 2.5YR, or 5YR
Value: 4 or 5 dry, 3 or 4 moist
Chroma: 4 or 6
Texture: clay
Clay content: 60 to 75 percent
Rock fragments: 0 to 10 percent pebbles
Reaction: pH 7.4 to 7.8
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING: The Armington soils are on fans and uplands. Elevations are 3,600 to 6,000 feet. Slopes are 2 to 35 percent. These soils formed in alluvium. The climate is characterized by long, cold winters; moist springs; and warm summers. Mean annual precipitation is 15 to 19 inches. Mean annual temperature is 40 to 44 degrees F. The frost-free period is 90 to 120 days.
DRAINAGE AND PERMEABILITY: Well drained; rapid runoff; very slow permeability.
USE AND VEGETATION: Armington soils are used mainly as rangeland. Potential native vegetation is mainly bluebunch wheatgrass, green needlegrass, western wheatgrass, and Idaho fescue.
DISTRIBUTION AND EXTENT: Armington soils are of moderate extent in central and southern Montana.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Big Horn County (Area), Montana, 1970.
REMARKS: Soil Interpretation Records: MT0582. Diagnostic horizons and features recognized in this pedon are: a mollic epipedon from the soil surface to 11 inches (A, Bw1 horizons); cambic horizons from 11 to 33 inches (Bw2, Bw3 horizons); a particle-size control section from 10 to 40 inches (Bw1, Bw2, Bw3, and BC horizons); few nonintersecting slickensides in Bw2 and Bw3 horizons. Vertic Haploborolls feature a mollic epipedon and a cambic horizon. They also have cracks that are 1/4 inch or more wide at a depth of 20 inches in most years, potential linear extensibility of 2 inches or more in the upper 40 inches, and more than 35 percent clay in horizons that are greater than 20 inches thick. Armington soils have an ustic moisture regime and a frigid temperature regime.