LOCATION SIXBEACON MTEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, frigid Aridic Haplustolls
TYPICAL PEDON: Sixbeacon gravelly loam, irrigated hayland (colors are for dry soil unless otherwise noted).
Ap--0 to 4 inches; grayish brown (10YR 5/2) gravelly loam, very dark grayish brown (10YR 3/2) moist; moderate fine granular structure; soft, very friable, nonsticky and nonplastic; many fine roots; many fine irregular pores; 15 percent pebbles; neutral (pH 6.8); abrupt smooth boundary. (4 to 9 inches thick)
Bw--4 to 10 inches; brown (10YR 5/3) loam, dark brown (10YR 3/3) moist; moderate medium subangular blocky structure; hard, friable, slightly sticky and slightly plastic; many fine roots; many fine and very fine tubular pores; 5 percent pebbles; neutral (pH 7.2); clear wavy boundary. (4 to 6 inches thick)
Bk1--10 to 12 inches; light brownish gray (10YR 6/2) loam, brown (10YR 5/3) moist; weak fine and medium subangular blocky structure; slightly hard, very friable, slightly sticky and slightly plastic; common fine roots; many fine and very fine pores; 10 percent pebbles; disseminated lime; strongly effervescent; moderately alkaline (pH 8.0); clear wavy boundary. (2 to 4 inches thick)
2Bk2--12 to 24 inches; white (10YR 8/2) very gravelly sandy loam, light gray (10YR 7/2) moist; weak fine subangular blocky structure; slightly hard, very friable, nonsticky and nonplastic; common fine roots; many fine and very fine tubular pores; 50 percent pebbles; disseminated lime; violently effervescent; moderately alkaline (pH 8.4); clear wavy boundary. (10 to 23 inches thick)
3Bk3--24 to 60 inches; light gray (10YR 7/2) extremely gravelly loamy sand, pale brown (10YR 6/3) moist; single grain; loose, nonsticky and nonplastic; few fine roots; many fine irregular pores; 60 percent pebbles and 10 percent cobbles; disseminated lime; violently effervescent; moderately alkaline (pH 8.4).
TYPE LOCATION: Powell County, Montana; 100 feet north and 1,000 feet west of the SE corner of sec. 23, T. 8 N., R. 9 W.
RANGE IN CHARACTERISTICS:
Soil temperature - 41 to 47 degrees F.
Moisture control section - between 4 and 12 inches; dry in all parts between four-tenths and five-tenths of the cumulative days per year when the soil temperature at a depth of 20 inches is 41 degrees F or higher.
Mollic epipedon thickness - 7 to 15 inches.
Depth to calcic horizon - 8 to 13 inches.
Ap horizon - Hue: 10YR or 2.5Y
Chroma: 2 or 3
Texture: loam, fine sandy loam or sandy loam
Clay content: 10 to 27 percent
Rock fragments: 0 to 35 percent--0 to 15 percent cobbles; 0 to 20 percent pebbles
Reaction: pH 6.1 to 7.8
Bw horizon - Hue: 10YR or 2.5Y
Value: 4, 5 or 6 dry; 3 or 4 moist
Chroma: 2, 3, or 4
Texture: loam or sandy loam
Clay content: 18 to 27 percent
Rock fragments: 0 to 35 percent--0 to 10 percent cobbles; 0 to 25 percent pebbles
Reaction: pH 6.6 to 8.4
Bk1 horizon - Hue: 10YR or 2.5Y
Value: 5, 6, 7 or 8 dry, 4, 5, 6 or 7 moist
Chroma: 1, 2, 3, or 4
Texture: loam or sandy loam
Clay content: 10 to 27 percent
Rock fragments: 5 to 35 percent--0 to 5 percent cobbles; 5 to 30 percent pebbles
Calcium carbonate equivalent: 5 to 25 percent
Reaction: pH 7.4 to 8.4
2Bk2 horizon - Hue: 10YR or 2.5Y
Value: 6, 7 or 8 dry; 6 or 7 moist
Chroma: 2, 3, or 4
Texture: sandy loam or loam
Clay content: 10 to 20 percent
Rock fragments: 35 to 60 percent--0 to 10 percent cobbles; 35 to 50 percent pebbles
Calcium carbonate equivalent: 20 to 40 percent
Reaction: pH 7.9 to 8.4
3Bk3 horizon - Value: 5, 6, or 7 dry; 4, 5, or 6 moist
Chroma: 2, 3, or 4
Texture: loamy sand, sandy loam, or loam
Clay content: 0 to 10 percent
Rock fragments: 50 to 80 percent--10 to 20 percent cobbles; 40 to 60 percent pebbles
Calcium carbonate equivalent: 15 to 30 percent
Reaction: pH 7.4 to 9.0
COMPETING SERIES:
Bulltop (ND) - averages more than 18 percent clay in the particle-size control section
Dolus (MT) - has a paralithic contact of semiconsolidated sandstone at depths of 20 to 40 inches.
Frenchcreek (MT) - does not have a horizon of secondary calcium carbonate accumulations or a calcic horizon.
GEOGRAPHIC SETTING:
Landform - alluvial fans, stream terraces and valley floors.
Elevation - 3,600 to 5,800 feet.
Slope- 0 to 60 percent.
Parent material - gravelly alluvium.
Climate - long, cold winters.
Mean annual precipitation - 10 to 14 inches.
Mean annual air temperature - 39 to 45 degrees F.
Frost-free period - 90 to 115 days.
DRAINAGE AND PERMEABILITY: Well drained; moderate permeability above the sandy-skeletal material and rapid in the sandy-skeletal material.
USE AND VEGETATION: Sixbeacon soils are used mainly for rangeland and irrigated cropland. Potential native vegetation is mainly bluebunch wheatgrass, green needlegrass, needleandthread, Sandberg bluegrass, prairie junegrass, and forbs.
DISTRIBUTION AND EXTENT: Sixbeacon soils are of small extent in mountain valleys of western Montana.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Powell County, Montana, 1995.
REMARKS: Soil interpretations record: MT0618, MT8150. Diagnostic horizons and features recognized in this pedon are: a mollic epipedon from the soil surface to 10 inches (A, Bw horizons); a calcic horizon from 12 to 60 inches (2Bk2, 3Bk3 horizons); a particle-size control section from 10 to 40 inches (Bk1, 2Bk2, 3Bk3 horizons). Sixbeacon soils have a frigid temperature regime and an ustic moisture regime that borders on aridic.