LOCATION ROCKHILL MTEstablished Series
TAXONOMIC CLASS: Ashy-skeletal, mixed, frigid Lithic Udivitrands
TYPICAL PEDON: Rockhill very gravelly silt loam, forested (colors are for dry soil unless otherwise noted).
Oi--0 to 1 inch; undecomposed and slightly decomposed forest litter. (1 to 2 inches thick)
A--1 to 5 inches; brown (10YR 5/3) very gravelly ashy silt loam, dark brown (10YR 3/3) moist; weak fine granular structure; soft, very friable, nonsticky and nonplastic; common very fine and fine roots; 5 percent cobbles, 40 percent gravel; slightly acid (pH 6.2); clear smooth boundary. (1 to 4 inches thick)
Bw--5 to 14 inches; light yellowish brown (10YR 6/4) very gravelly ashy silt loam, dark yellowish brown (10YR 4/4) moist; weak fine subangular blocky structure parting to weak fine granular; soft, very friable, nonsticky and nonplastic; common very fine and fine roots; 5 percent cobbles, 50 percent gravel; slightly acid (pH 6.2); clear wavy boundary. (9 to 15 inches thick)
2C--14 to 19 inches; light yellowish brown (10YR 6/4) extremely gravelly silt loam, dark yellowish brown (10YR 4/4) moist; massive; soft, very friable, nonsticky and nonplastic; few fine and medium roots; 10 percent cobbles, 65 percent gravel; slightly acid (pH 6.2); abrupt wavy boundary. (0 to 6 inches thick)
R--19 inches; fractured argillite and quartzite bedrock.
TYPE LOCATION: Lincoln County, Montana; 800 feet south and 1100 feet east of the northwest corner of section 19, T. 27N., R. 28W.
RANGE IN CHARACTERISTICS:
Soil temperature - 42 to 47 degrees F.
Depth to bedrock - 10 to 20 inches from the mineral soil surface.
Volcanic glass content - in the 0.02 to 2.0 mm fraction - 5 to 30 percent.
Acid-oxalate extractable Al + 1/2 Fe: 0.4 to 2.0.
Phosphate retention - 25 to 75 percent.
15-bar water retention on air dried samples - 8 to 12 percent.
A horizon
Value: 4 or 5 dry, 2 or 3 moist
Clay content: 5 to 10 percent
Rock fragments: 35 to 60 percent; 0 to 10 percent cobbles, 35 to 50 percent gravel
Moist bulk density: 0.85 to 1.00 g/cc
Reaction: 5.6 to 6.5
Bw horizon
Value: 5, 6, or 7 dry, 3, 4, 5, or 6 moist
Chroma: 4 or 6
Texture: ashy silt loam or ashy loam
Clay content: 5 to 10 percent
Rock fragments: 35 to 60 percent; 5 to 10 percent cobbles, 30 to 50 percent gravel
Moist bulk density: 0.85 to 1.00 g/cc
Reaction: 5.6 to 6.5
2C horizon
Value: 5, 6, or 7 dry; 4, 5, or 6 moist
Texture: silt loam or loam
Clay content: 5 to 10 percent
Rock fragments: 60 to 85 percent; 10 to 20 percent cobbles, 45 to 65 percent gravel
Reaction: 5.6 to 6.5
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING:
Landform- mountains.
Elevation - 2,200 to 6,000 feet.
Slope - 4 to 70 percent.
Parent material - colluvium or residuum derived from argillite and quartzite bedrock with a mantle of volcanic ash.
Climate - long, cold winters; moist springs; warm summers.
Mean annual precipitation - 24 to 32 inches.
Mean annual temperature - 39 to 45 degrees F.
Frost-free period - 70 to 90 days.
GEOGRAPHICALLY ASSOCIATED SOILS:
DRAINAGE AND PERMEABILITY: Well drained, moderate permeability.
USE AND VEGETATION: Rockhill soils are used mainly for woodland, understory grazing, and wildlife habitat. Potential native vegetation is mainly ponderosa pine, Douglas fir, western larch, and lodgepole pine. Understory vegetation is mainly oceanspray, snowberry, mallow ninebark, pinegrass, heartleaf arnica, Saskatoon serviceberry, and other grasses, forbs, and shrubs.
DISTRIBUTION AND EXTENT: Rockhill soils are of moderate extent in the mountains of northwestern Montana. MLRA 43A.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Sanders County, Montana 1997.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - 0 to 7 inches (Oi, A, Bw horizons);
Cambic horizon - 5 to 14 inches (Bw horizon);
Particle size control section - 1 to 18 inches (A, Bw, 2C horizons); and
Lithic contact - at 19 inches (R horizon).
Rockhill soils have andic soil properties, a udic moisture regime, and a frigid temperature regime.
ADDITIONAL DATA: Soil Interpretation Record MT1541.