LOCATION BIGNELL MTEstablished Series
TAXONOMIC CLASS: Clayey-skeletal, mixed, superactive, frigid Typic Haplustalfs
TYPICAL PEDON: Bignell gravelly loam, forested (colors are for dry soil unless otherwise noted).
Oi--0 to 2 inches; undecomposed and slightly decomposed forest litter. (1 to 2 inches thick)
E--2 to 13 inches; pinkish gray (7.5YR 7/2) gravelly loam, pinkish gray (7.5YR 6/2) moist; weak fine subangular blocky structure; soft, very friable, nonsticky and nonplastic; common very fine and fine roots; common very fine and fine pores; 20 percent pebbles; strongly acid (pH 5.5); abrupt wavy boundary. (5 to 16 inches thick)
E/Bt--13 to 17 inches; E part (80 percent) is pinkish gray (7.5YR 7/2) very gravelly loam, pinkish gray (7.5YR 6/2) moist tongues; B part (20 percent) pinkish gray (7.5YR 6/2) very gravelly clay loam, brown (7.5YR 5/2) moist; texture mixed is very gravelly loam; moderate medium subangular blocky structure; slightly hard, very friable, nonsticky and nonplastic; common very fine and fine roots; common very fine and fine pores; 45 percent pebbles; strongly acid (pH 5.5); gradual wavy boundary. (2 to 11 inches thick).
Bt1--17 to 37 inches; light brown (7.5YR 6/4) very gravelly clay, brown (7.5YR 5/4) moist; strong fine and medium angular blocky structure; very hard, firm, moderately sticky and very plastic; few very fine, fine, medium, and coarse roots; common very fine and fine pores; common distinct clay films on faces of peds; common distinct clay films on pebbles; 45 percent pebbles; strongly acid (pH 5.5); clear wavy boundary. (7 to 45 inches thick)
Bt2--37 to 60 inches; light brown (7.5YR 6/4) very gravelly clay, strong brown (7.5YR 5/6) moist; strong fine and medium angular blocky structure; very hard, firm, moderately sticky and very plastic; few very fine, fine, medium, and coarse roots; few very fine and fine pores; reddish yellow (7.5YR 7/8) and brown (7.5YR 5/4) moist; common distinct clay films on faces of peds; common distinct clay films on surface of pebbles; 45 percent pebbles; moderately acid (pH 6.0).
TYPE LOCATION: Missoula County, Montana; approximately 800 feet north and 300 feet east of the SW corner of sec. 30, T. 14 N., R. 16 W.
RANGE IN CHARACTERISTICS:
Soil temperature - 40 to 46 degrees F.
Moisture control section - between 4 and 12 inches.
Surface stones: 0 to 3 percent
Some pedons have a Bt/E horizon 6 to 12 inches thick in place of or in addition to the E/Bt horizon.
E horizons - Hue: 7.5YR or 10YR
Value: 5, 6 or 7 dry; 4, 5, or 6 moist
Chroma: 1, 2, 3, or 4
Texture: loam or clay loam
Clay content: 10 to 30 percent
Rock fragments: 15 to 60 percent--0 to 30 percent cobbles or stones, 10 to 30 percent pebbles
Reaction: pH 5.1 to 7.8
E/Bt or Bt/E horizons - Hue: 7.5YR or 10YR
Value: E part 5, 6 or 7 dry, 4, 5 or 6 moist; B part 4, 5, 6, or 7 dry
Chroma: E part 1, 2 or 3; B part 2, 3, 4, or 6
Texture: loam, sandy clay loam, clay loam
Clay content: 10 to 40 percent
Rock fragments: 25 to 60 percent--0 to 35 percent cobbles, 15 to 55 percent pebbles
Reaction: pH 5.1 to 7.8
Bt horizons - Hue: 5YR, 7.5YR, or 10YR
Value: 4, 5, 6, or 7 dry; 3, 4, 5, or 6 moist
Chroma: 2, 3, 4, or 6
Texture: clay, sandy clay, or clay loam
Clay content: 35 to 60 percent
Rock fragments: 35 to 60 percent--0 to 40 percent cobbles, 15 to 45 percent pebbles
Reaction: pH 5.1 to 6.5; below 40 inches the pH can range to 7.8.
COMPETING SERIES:
Trampas (NM) - does not have E/Bt horizon.
GEOGRAPHIC SETTING:
Landform - moraines, alluvial fans, stream terraces, hills, and mountains.
Elevation - 2,600 to 6,900 feet.
Slope - 0 to 60 percent.
Parent material - alluvium and colluvium from fine grained extrusive igneous rocks in Tertiary sediment, some of which was redeposited as till.
Climate - long, cold winters; moist springs; warm summers.
Mean annual precipitation - 15 to 30 inches, much of which falls as snow and as spring rain.
Mean annual temperature - 38 to 44 degrees F.
Frost-free season - 70 to 105 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Crow, Greenough, Lubrecht, and Shooflin soils. These soils have less than 35 percent rock fragments throughout. Shooflin soils are very fine.
DRAINAGE AND PERMEABILITY: Well drained; slow permeability.
USE AND VEGETATION: Bignell soils are used for timber production, wildlife habitat, and for watersheds. The native vegetation is coniferous forest consisting of ponderosa pine, western larch, and Douglas fir with an understory of elk sedge, pinegrass, common snowberry, dwarf huckleberry, twinflower, and blue huckleberry.
DISTRIBUTION AND EXTENT: Bignell soils are of moderate extent in western Montana.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana.
SERIES ESTABLISHED: Missoula County, Montana, 1985.
REMARKS: Soil interpretation record: MT1065, MT0395, MT8169. Diagnostic horizons and features recognized in this pedon are: an albic horizon from 2 to 13 inches (E horizon); a glossic horizon from 13 to 17 inches (E/Bt horizon); an argillic horizon from 17 to 60 inches (Bt1, Bt2 horizons); a particle-size control section from 17 to 37 inches (Bt1 horizon). Bignell soils have an ustic moisture regime and a frigid temperature regime.