LOCATION ELKROCK MTEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, frigid Vitrandic Haploxerepts
TYPICAL PEDON: Elkrock cobbly ashy silt loam, forested (colors are for dry soil unless otherwise noted).
Oi--0 to 2 inches; undecomposed and slightly decomposed forest litter.
A--2 to 4 inches; dark gray (10YR 4/1) cobbly ashy silt loam, very dark gray (10YR 3/1) moist; weak fine subangular blocky structure; soft, very friable, slightly sticky and slightly plastic; many very fine, fine, medium, and common coarse roots; 15 percent cobbles and 10 percent pebbles; slightly acid (pH 6.4); clear wavy boundary. (1 to 5 inches thick)
Bw--4 to 15 inches; very pale brown (10YR 7/3) very gravelly ashy silt loam, brown (10YR 5/3) moist; weak fine subangular blocky structure; soft, very friable, slightly sticky and slightly plastic; many very fine, fine, medium, and common coarse roots; 15 percent cobbles and 35 percent pebbles; moderately acid (pH 6.0); clear wavy boundary. (10 to 40 inches thick)
2C--15 to 60 inches; very pale brown (10YR 7/3) extremely cobbly loam, pale brown (10YR 6/3) moist; massive; soft, very friable, slightly sticky and slightly plastic; few very fine, fine, medium, and coarse roots; 40 percent cobbles and 30 percent pebbles; moderately acid (pH 5.8).
TYPE LOCATION: Sanders County, Montana; 1,500 feet south and 2,400 feet west of the NE corner of sec. 17, T. 20 N., R. 26 W.
RANGE IN CHARACTERISTICS:
Soil temperature - 44 to 47 degrees F.
Moisture control section - between 8 and 24 inches; dry for more than 45 consecutive days in the four months following the summer solstice.
Thickness of ash component - 11 to 35 inches
A horizon - Value: 4, 5, or 6 dry; 3 or 4 moist
Chroma: 1 or 2
Clay content: 7 to 20 percent
Rock fragments: 15 to 35 percent--0 to 5 percent stones, 5 to 15 percent cobbles, and 10 to 15 percent pebbles
Volcanic glass content: 5 to 20 percent
AOE Al plus 1/2 Fe: .4 to 1 percent
Bulk density: 1.0 to 1.3 g/cc
Reaction: pH 6.1 to 7.3
This horizon when mixed to 7 inches does not meet the requirements of a mollic epipedon.
Bw horizon - Value: 6 or 7 dry, 4 or 5 moist
Chroma: 2, 3, or 4
Texture: ashy silt loam, ashy loam, or ashy sandy loam
Clay content: 7 to 20 percent
Rock fragments: 35 to 60 percent--5 to 15 percent cobbles, 30 to 45 percent pebbles
Volcanic glass content: 5 to 20 percent
AOE Al plus 1/2 Fe: .4 to 1 percent
Bulk density: 1.0 to 1.3 g/cc
Reaction: pH 5.6 to 7.3
2C horizon - Value: 7 or 8 dry, 5 or 6 moist
Chroma: 2, 3, or 4
Texture: loam or sandy loam
Clay content: 7 to 20 percent
Rock fragments: 60 to 80 percent--30 to 40 percent cobbles, 30 to 40 percent pebbles
Reaction: pH 5.6 to 7.3
COMPETING SERIES:
Brevco (WA) - have a lithic contact of granite bedrock at 20 to 40 inches.
Coxit (WA) - have a mean annual soil temperature of 42 to 45 degrees F.; have laess than 60 percent rock fragments in the C horizon.
Highhorn (OR) - have a lithic contact at 40 to 60 inches.
Huntrock (OR) - have a lithic contact at 20 to 40 inches.
Jimbluff (WA) - have 2 to 6 percent clay in the particle-size control section.
Lambutte (WA) - have a lithic contact at 40 to 60 inches.
Lekrem (WA) - have less than 60 percent coarse fragments in the 2C horizon.
Longort (WA) - have less than 60 percent coarse fragments in the 2C horizon; have a dense layer.
Noil (ID) - have a paralithic contact at 40 to 60 inches.
Ontrail (WA) - have less than 60 percent coarse fragments in the 2C horizon.
Redpeak (WA) - have a lithic contact at 20 to 40 inches.
Santop (WA) - have a lithic contact at 20 to 40 inches.
Seeburg (WA) - have 4 to 7 percent clay in the particle-size control section.
GEOGRAPHIC SETTING:
Landform - alluvial fans, stream terraces, and hills.
Elevation - 2,400 to 2,900 feet.
Slope - 0 to 60 percent.
Parent material - alluvium.
Climate - long, cold winters; moist springs; warm summers.
Mean annual precipitation - 17 to 24 inches, much of which falls as snow and spring rain.
Mean annual temperature - 43 to 45 degrees F.
Frost-free period - 105 to 125 days.
DRAINAGE AND PERMEABILITY: Somewhat excessively drained; moderately rapid permeability.
USE AND VEGETATION: Elkrock soils are used for timber production, understory grazing, and wildlife habitat. The native vegetation is coniferous forest consisting of ponderosa pine and Douglas fir with an understory of rough fescue, Idaho fescue, Saskatoon serviceberry, white spirea and antelope bitterbrush.
DISTRIBUTION AND EXTENT: Elkrock soils are of small extent in western Montana.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Sanders County, Montana, 1997.
REMARKS: Soil interpretation record: MT1292. Diagnostic horizons and features recognized in this pedon are: an ash influenced layer from 2 to 15 inches (A, Bw horizons); an ochric epipedon from the mineral soil surface to 7 inches (A, Bw horizons); a cambic horizon from 4 to 15 inches (Bw horizon); a particle-size control section from 10 to 40 inches below the mineral soil surface (Bw, 2C horizon). Elkrock soils have a frigid temperature regime and a xeric moisture regime.
ADDITIONAL DATA: Laboratory sample S91MT-89-003.