LOCATION COEROCK MTEstablished Series
The Coerock series consists of shallow, well drained soils that formed in volcanic ash over argillite or quartzite bedrock. These soils are on mountain slopes and ridgetops and in glaciated mountain basins. Slopes are 4 to 80 percent. Mean annual precipitation is about 60 inches, and mean annual temperature is about 35 degrees F.
TAXONOMIC CLASS: Medial-skeletal, amorphic Lithic Vitricryands
TYPICAL PEDON: Coerock very gravelly medial silt loam, forested. (Colors are for dry soil unless otherwise noted.)
0i--0 to 1 inch; undecomposed and slightly decomposed forest litter.
Bw1--1 to 16 inches; reddish yellow (7.5YR 6/6) very gravelly medial silt loam, strong brown (7.5YR 4/6) moist; weak fine and medium granular structure; soft, very friable, nonsticky, and nonplastic; many very fine, fine, and medium roots and few coarse roots; 40 percent pebbles; moderately acid (pH 6.0); gradual wavy boundary.
Bw2--16 to 19 inches; light brown (7.5YR 6/4) very gravelly medial loam, brown (7.5YR 4/4) moist; weak medium subangular blocky structure; soft, very friable, nonsticky, and nonplastic; common very fine, fine, and medium roots and few coarse roots; 35 percent pebbles, 10 percent cobbles; moderately acid (pH 6.0); abrupt wavy boundary. (Combined thickness of Bs horizons is 14 to 20 inches.)
R--19 inches; fractured quartzite bedrock.
TYPE LOCATION: Missoula County, Montana; approximately 2,000 feet west and 1,000 feet south of the NE corner of sec. 2, T. 17 N., R. 17 W.
RANGE IN CHARACTERISTICS:
Soil temperature - 35 to 38 degrees F.
Moisture control section - approximately between the depths of 8 and 19 inches.
Control section - 7 to 15 percent clay
Depth to bedrock - 14 to 20 inches below the mineral soil surface
Base saturation - less than 60 percent
NOTE: In some pedons there is an E horizon that is 1 inch to 2 inches thick.
Bw1 horizon - Hue: 7.5YR or 10YR
Value: 5, 6, or 7 dry; 3, 4, or 5 moist
Chroma: 3, 4, or 6
Texture, greater than 2 mm: medial silt loam or medial loam
Clay content: 7 to 15 percent
Rock fragments: 35 to 60 percent--0 to 10 percent cobbles; 35 to 50 percent pebbles
Reaction: pH 5.6 to 6.5
Moist bulk density: less than 0.85 g/cc
Bw2 horizon - Hue: 7.5YR or 10YR
Value: 5, 6, or 7 dry; 3, 4, or 5 moist
Chroma: 3, 4, or 6
Texture, greater than 2 mm: medial loam or medial silt loam
Clay content: 7 to 15 percent
Rock fragments: 35 to 50 percent--5 to 15 percent cobbles; 30 to 45 percent pebbles
Reaction: pH 5.6 to 6.5
Moist bulk density: less than 0.85 g/cc
COMPETING SERIES: This is the Partov series and the similar Culvop series. Partov soils are 60 to 80 percent basalt fragments in the particle-size control section. Culvop soils are ashy-skeletal.
GEOGRAPHIC SETTING: Coerock soils are on mountain slopes and ridgetops and in glaciated mountain basins. Elevations are 6,500 to 8,000 feet. Slopes are 4 to 80 percent. These soils formed in volcanic ash over argillite or quartzite bedrock. The climate is characterized by long, cold winters and moist springs. Mean annual precipitation is 50 to 80 inches, much of which falls as snow and as spring rain. Mean annual temperature is 33 to 36 degrees F. The frost-free period is less than 40 days.
DRAINAGE AND PERMEABILITY: Well drained; medium to very rapid runoff; moderate permeability.
USE AND VEGETATION: Coerock soils are used as wildlife habitat and for watersheds. The native vegetation is subalpine fir, Engelmann spruce, whitebark pine, and alpine larch with an understory of Hitchcocks woodrush, grouse whortleberry, mountain heath, rusty menziesia, and common beargrass.
DISTRIBUTION AND EXTENT: Coerock soils are of moderate extent in western Montana.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Mineral County, Montana, 1970.
REMARKS: Soil Interpretation Records: MT0400, MT0725. Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon from the soil surface to 7 inches (Oi and Bw1 horizon);
Cambic horizon from 7 to 18 inches (Bw1, Bw2 horizons);
Moist bulk density less than 0.85 g/cc from the soil surface to 19 inches (Bw1, Bw2 horizons);
Less than 60 percent of the soil is volcanic ash;
a particle-size control section from the mineral soil surface to 19 inches (Bw1, Bw2 horizons).
Coerock soils have a cryic temperature regime and a udic moisture regime.
No 15 bar water data are available on these soils. The classification is based on an assumed value of between 12 and 15 percent.