LOCATION BONNASH MTEstablished Series
TAXONOMIC CLASS: Ashy over loamy-skeletal, amorphic over mixed, superactive, frigid Typic Udivitrands
TYPICAL PEDON: Bonnash gravelly ashy silt loam, forested (colors are for moist soil unless otherwise noted).
Oi--0 to 2 inches; undecomposed and slightly decomposed forest litter.
A--2 to 5 inches; very dark grayish brown (10YR 3/2) gravelly silt ashy loam, dark grayish brown (10YR 4/2) dry; weak fine granular structure; soft, very friable, nonsticky and nonplastic; many very fine, fine, medium and coarse roots; 5 percent cobbles, 15 percent pebbles; slightly acid (pH 6.4); clear wavy boundary. (0 to 3 inches thick)
Bw1--5 to 16 inches; dark yellowish brown (10YR 4/4) gravelly ashy silt loam, yellowish brown (10YR 5/4) dry; weak fine and medium subangular blocky structure; soft, very friable, nonsticky and slightly plastic; many very fine, fine, medium and coarse roots; 5 percent cobbles, 15 percent pebbles; slightly acid (pH 6.4); gradual wavy boundary. (9 to 14 inches thick)
Bw2--16 to 26 inches; yellowish brown (10YR 5/4) gravelly ashy silt loam, light yellowish brown (10YR 6/4) dry; weak fine and medium subangular blocky structure; soft, very friable, nonsticky and slightly plastic; many very fine, fine, medium and coarse roots; 5 percent cobbles, 15 percent pebbles; slightly acid (pH 6.2); gradual irregular boundary. (5 to 12 inches thick)
2E/Bw--26 to 37 inches; E part (60 percent) is yellowish brown (10YR 5/4) very gravelly sandy loam, light yellowish brown (10YR 6/4) dry, Bw part (40 percent) is dark yellowish brown (10YR 4/6) very gravelly sandy loam, yellowish brown (10YR 5/6) dry; moderate medium subangular blocky structure; slightly hard, very friable, slightly sticky and slightly plastic; common fine, medium and coarse roots; 10 percent cobbles, 30 percent pebbles; moderately acid (pH 5.8); clear wavy boundary. (8 to 20 inches thick)
2C--37 to 60 inches; yellowish brown (10YR 5/4) extremely cobbly loamy coarse sand, light yellowish brown (10YR 6/4) dry; single grain; loose, nonsticky and nonplastic; few fine, medium and coarse roots; 25 percent cobbles, 40 percent pebbles; moderately acid (pH 6.0).
TYPE LOCATION: Sanders County, Montana; 1000 feet north and 900 feet west of the southeast corner of section 16, T. 23 N., R. 30 W.
RANGE IN CHARACTERISTICS:
Soil temperature - 43 to 47 degrees
Volcanic ash mantle - 14 to 28 inches thick
Volcanic glass content in the 0.02 to 2.0 mm fraction - 5 to 30 percent
Acid-oxalate extractable Al plus 1/2 Fe - 0.40 to 2.0 percent
Phosphate retention - 25 to 90 percent
15-bar water retention on air dried samples - 5 to 12 percent
A horizon - Value: 4, 5, or 6 dry, 3, 4, or 5 moist
Clay content: 2 to 10 percent
Bulk density: 0.85 - 1.00 g/cc
Rock Fragments: 15 to 25 percent--0 to 5 percent cobbles, 15 to 20 percent pebbles
Reaction: 5.6 to 6.5
Bw1 horizon - Value: 4, 5, or 6 dry, 3, 4, or 5 moist
Clay content: 2 to 10 percent
Bulk density: 0.85 - 1.00 g/cc
Rock Fragments: 15 to 25 percent--0 to 5 percent cobbles, 15 to 20 percent pebbles
Reaction: 5.6 to 6.5
Bw2 horizon - Value: 4, 5, or 6 dry, 3, 4, or 5 moist
Clay content: 2 to 10 percent
Bulk density: 0.85 - 1.00 g/cc
Rock Fragments: 15 to 25 percent--0 to 5 percent cobbles, 15 to 20 percent pebbles
Reaction: 5.6 to 6.5
2E/Bw horizon - Value: E part 5, 6, or 7, B part 4, 5, or 6 dry; E part 4, 5, or 6, B part 3, 4, or 5 moist
Clay content: 2 to 10 percent
Rock Fragments: 35 to 55 percent--5 to 15 percent cobbles, 30 to 40 percent pebbles
Reaction: 5.6 to 7.3
2C horizon - Value: 5, 6, or 7 dry, 4, 5, or 6 moist
Clay content: 2 to 10 percent
Rock Fragments: 60 to 90 percent--20 to 40 percent cobbles, 40 to 50 percent pebbles
Reaction: 5.6 to 7.3
COMPETING SERIES:
Ahrs (ID) - has 35 to 60 percent coarse fragments in the Bw horizon.
Bouldercreek (ID) - does not have 2E/Bw horizon; has 2BC horizon; formed in material from schist or quartzite bedrock.
Dewberry (MT) - does not have 2E/Bw horizon.
Ferguson (OR) - does not have 2E/Bw horzizon; has 2Bw horizon; formed in glaciofluvial deposits predominantly from granite.
Honeyjones (ID) - does not have 2E/Bw horizon; has 2Bw horizon; formed in material from metasedimentary bedrock mainly siltite and quartzite.
Stevie (MT) - is excessively drained; formed in colluvium.
GEOGRAPHIC SETTING:
Landform - stream terraces in valleys.
Elevation - 2200 to 2600 feet.
Slope - 0 to 35 percent.
Parent material - mixed alluvium and glacial outwash with a mantle of volcanic ash.
Climate - long, cold winters; moist springs; and warm summers.
Mean annual precipitation - 24 to 28 inches.
Mean annual temperature - 42 to 45 degrees F.
Frost-free period - 90 to 105 days.
DRAINAGE AND PERMEABILITY: Well drained, moderate over very rapid permeability.
USE AND VEGETATION: Bonnash soils are used mainly for woodland, understory grazing, and wildlife habitat. Potential native vegetation is mainly ponderosa pine, Douglas fir, western larch, lodgepole pine, and grand fir. Understory vegetation is mainly oceanspray, starry false Solomons seal, western goldthread, pinegrass, common snowberry, queencup beadlily, twinflower, bracken fern, elk sedge, and other forbs, shrubs, and grasses.
DISTRIBUTION AND EXTENT: Bonnash soils are of small extent in the valleys of northwestern Montana.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana.
SERIES ESTABLISHED: Sanders County, Montana 1997.
REMARKS: Soil Interpretation Record: MT1383. Diagnostic horizons and features recognized in this pedon are: a volcanic ash mantle from 2 to 26 inches (A, Bw1, Bw2 horizons); an ochric epipedon from 2 to 9 inches (A, Bw1 horizons); a cambic horizon from 5 to 26 inches (Bw horizons); a particle size control section from 2 to 42 inches (A, Bw1, Bw2, 2E/Bw, 2C horizons). Bonnash soils have a udic moisture regime and a frigid temperature regime.