LOCATION VALLEYFLAT MTEstablished Series
TAXONOMIC CLASS: Sandy, mixed, frigid Aridic Haplustolls
TYPICAL PEDON: Valleyflat coarse sandy loam, in grassland (colors are for dry soil unless otherwise noted).
A1--0 to 2 inches; brown (10YR 5/3) coarse sandy loam, very dark grayish brown (10YR 3/2) moist; weak very thin platy structure; soft, very friable, slightly sticky and slightly plastic; common very fine and few fine roots; 5 percent, mainly fine, gravel; strongly acid (pH 5.2); clear smooth boundary. (1 to 3 inches thick)
A2--2 to 5 inches; brown (10YR 5/3) sandy loam, very dark grayish brown (10YR 3/2) moist; weak very thin platy structure; soft, very friable, slightly sticky and slightly plastic; many very fine and common fine roots; 5 percent, mainly fine, gravel; slightly acid (pH 6.2); clear smooth boundary. (3 to 5 inches thick)
Bw--5 to 11 inches; yellowish brown (10YR 5/4) sandy loam, dark yellowish brown (10YR 3/4) moist; moderate, medium to coarse, subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine and few fine roots; few, faint clay bridges between sand grains; 10 percent, mainly fine, gravel; neutral (pH 6.8); clear wavy boundary. (4 to 12 inches thick)
2C1--11 to 40 inches; variegated very pale brown (10YR 8/2) and very pale brown (10YR 7/3) gravelly coarse sand with thin strata of very gravelly coarse sand, light yellowish brown (10YR 6/4) moist; single grain; loose, non-sticky and non-plastic; few very fine roots; 30 percent, mainly fine, gravel; neutral (pH 7.2); diffuse smooth boundary. (25 to 35 inches thick)
2C2--40 to 72 inches; variegated very pale brown (10YR 8/2) and very pale brown (10YR 7/3) gravelly coarse sand with thin strata of very gravelly coarse sand, light yellowish brown (10YR 6/4) moist; single grain; loose, non-sticky and non-plastic; 35 percent, mainly fine, gravel; neutral (pH 7.2); diffuse smooth boundary.
TYPE LOCATION: Silver Bow County, Montana; 2450 feet north and 500 feet west of the SE corner of sec. 8, T.2 N., R.7 W. Homestake topographic quadrangle, Latitude 45 degrees 56 minutes 16 seconds N. and Longitude 112 degrees 29 minutes 23 seconds W.
RANGE IN CHARACTERISTICS:
Mean annual soil temperature - 40 to 46 degrees F., frigid temperature regime.
Soil moisture control section - between 12 and 35 inches; dry more than four-tenths of the cumulative days per year when the soil temperature at a depth of 20 inches is at or above 41 degrees F. Ustic moisture regime bordering on aridic.
Mollic epipedon thickness - 7 to 8 inches, mixed
Depth to 2C horizon - 8 to 20 inches
Some profiles have one or more thin strata of sandy loam material imbedded within predominantly sandy 2C horizon(s).
A1 Horizon
Value: 4 or 5 dry; 2 or 3 moist
Chroma: 2 or 3
Texture: coarse sandy loam, sandy loam or loam
Clay content: 5 to 18 percent
Rock fragments: 0 to 15 percent, mainly fine, gravel
Reaction: pH 4.5 to 6.5
A2 Horizon
Value: 4 or 5 dry; 2 or 3 moist
Chroma: 2 or 3
Texture: coarse sandy loam or sandy loam
Clay content: 5 to 18 percent
Rock fragments: 0 to 15 percent, mainly fine, gravel
Reaction: pH 5.6 to 7.3
Bw Horizon
Value: 5 or 6 dry; 3 or 4 moist
Chroma: 2, 3 or 4
Texture: coarse sandy loam or sandy loam
Clay content: 8 to 18 percent
Rock fragments: 5 to 20 percent, mainly fine, gravel
Reaction: pH 6.6 to 7.4
2C Horizons
Value: 6, 7 or 8 dry; 4, 5, 6 or 7 moist
Chroma: 2, 3 or 4
Texture: stratified coarse sand
Clay content: 0 to 4 percent
Rock fragments: 25 to 35 percent, mainly fine, gravel
Reaction: pH 6.6 to 7.8
COMPETING SERIES: This is the Ouray series. Ouray soils have less than 15 percent rock fragments throughout the soil profile.
GEOGRAPHIC SETTING:
Landform- valley bottoms, alluvial fans, stream terraces and hills.
Elevation - 4,950 to 5,970 feet.
Slope - 0 to 30 percent.
Parent material - granitic alluvium with some eolian influence in surface horizons.
Climate - long cold winters; moist springs; warm, dry summers
Mean annual precipitation - 10 to 14 inches
Mean annual air temperature - 38 to 44 degrees F.
Frost-free period - 70 to 100 days
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Pitchstone (T) and Rockerjohn (T) series. Pitchstone soils are coarse-loamy with the depth to sandy substrata greater than 24 inches. They occur in concave swales or on footslopes of adjacent escarpments or hills. Rockerjohn soils have lime present in one or more subsoil horizons. They occur on adjacent escarpments and footslopes.
DRAINAGE AND PERMEABILITY: Well drained; rapid permeability.
USE AND VEGETATION: Valleyflat soils are primarily used for rangeland and urban development. The native vegetation is mainly bluebunch wheatgrass, rubber rabbitbrush, Canada bluegrass, fringed sagewort, needleandthread grass and associated forbs.
DISTRIBUTION AND EXTENT: Valleyflat soils are of limited extent in valleys of southwestern Montana.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Silver Bow County, Montana, 2007.
REMARKS: Diagnostic horizons and features recognized in this pedon are: a mollic epipedon from the soil surface to 7 inches, mixed (A1, A2 and Bw horizons); a cambic horizon from 5 to 11 inches (Bw horizon); stratified coarse granitic alluvium from 11 to 72 inches (2C1 and 2C2 horizons); a particle-size control section from 10 to 40 inches (2C1 horizon). Valleyflat soils have a frigid temperature regime and an ustic moisture regime that borders on aridic. Gravel throughout the profile is primarily fine pea gravel less than 10 mm in diameter.