LOCATION PITCHSTONE MTEstablished Series
TAXONOMIC CLASS: Coarse-loamy, mixed, superactive, frigid Aridic Haplustolls
TYPICAL PEDON: Pitchstone coarse sandy loam, in grassland (colors are for dry soil unless otherwise noted).
A--0 to 5 inches; dark grayish brown (10YR 4/2) coarse sandy loam, very dark brown (10YR 2/2) moist; weak fine and medium granular structure; slightly hard, very friable, slightly sticky and slightly plastic; many very fine and fine and common medium roots; 5 percent, mainly fine, gravel; moderately acid (pH 6.0); clear smooth boundary. (5 to 15 inches thick)
Bw--5 to 12 inches; brown (10YR 5/3) gravelly coarse sandy loam, brown (10YR 4/3) moist; moderate medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine and fine and few medium roots; few very fine tubular pores; 15 percent, mainly fine, gravel; neutral (pH 6.6); clear smooth boundary. (6 to 24 inches thick)
BC--12 to 27 inches; pale brown (10YR 6/3) gravelly coarse sandy loam, brown (10YR 4/3) moist; massive; soft, very friable; non-sticky and non-plastic; few very fine and fine roots; 20 percent, mainly fine, gravel; neutral (pH 7.2); gradual smooth boundary (0 to 20 inches thick)
C1--27 to 40 inches; light brownish gray (2.5Y 6/2) gravelly loamy coarse sand, grayish brown (2.5Y 5/2) moist; single grain; loose, non-sticky and non-plastic; few very fine roots; abundant fine and very fine interstitial pores; 25 percent, mainly fine, gravel; slightly alkaline (pH 7.4); gradual smooth boundary. (10 to 25 inches thick)
C2--40 to 60 inches; light olive gray (5Y 6/2) gravelly coarse sand, olive gray (5Y 5/2) moist; single grain; loose, non-sticky and non-plastic; abundant fine and very fine interstitial pores; 30 percent, mainly fine, gravel; slightly alkaline (pH 7.4).
TYPE LOCATION: Silver Bow County, Montana; 2,600 feet north and 2,200 feet east of the southwest corner of sec. 18, T. 2 N., R. 7 W. Butte South topographic quadrangle, Latitude 45 degrees 55 minutes 24.7 seconds N. and Longitude 112 degrees 31 minutes 07.8 seconds W.
RANGE IN CHARACTERISTICS:
Mean annual soil temperature - 40 to 46 degrees F., frigid temperature regime.
Soil moisture control section - between 8 and 24 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 15 inches, mixed.
Depth to sandy substratum - 25 to 40 inches.
Rock fragments in the particle-size control section - 20 to 35 percent, mainly fine gravel.
These soils contain a high proportion of medium, coarse, and very coarse angular sand in the sand fraction due to granitic parent materials.
Some profiles have one or more thin strata of sandy loam material imbedded within the predominantly sandy C2 horizon.
Phases moderately impacted.
A Horizon
Hue: 10YR and 7.5YR
Value: 4 or 5 dry; 2 or 3 moist
Chroma: 2 or 3
Texture: coarse sandy loam, sandy loam, or loamy sand
Clay content: 6 to 18 percent
Rock fragments: 0 to 30 percent, mainly fine, gravel
Reaction: pH 5.4 to 7.0
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 25 percent, mainly fine, gravel
Reaction: pH 6.4 to 7.2
BC Horizon Value: 5 or 6 dry; 3 or 4 moist
Chroma: 3 or 4
Texture: coarse sandy loam or loamy coarse sand
Clay content: 4 to 12 percent
Rock fragments: 10 to 25 percent, mainly fine, gravel
Reaction: pH 6.8 to 7.6
C Horizons Hue: 10YR, 2.5Y or 5Y
Value: 5 or 6 dry; 4 or 5 moist
Chroma: 2, 3 or 4
Texture: coarse sand, loamy coarse sand, loamy sand or sand
Clay content: 0 to 6 percent
Rock fragments: 0 to 40 percent, mainly fine, gravel
Reaction: pH 7.2 to 8.0
COMPETING SERIES: These are the Anaconda, Chinook, Cozberg, Lahood, Modess, Pring, Rhame, Tinytown and Ynot series. Lahood soils have a lithic contact at 20 to 40 inches. Rhame and Modess soils have a paralithic contact at 20 to 40 inches. Anaconda and Cozberg soils have a calcic horizon. Chinook soils have horizons of accumulated calcium carbonate within 10 to 35 inches of the surface. Ynot and Pring soils do not have a sandy or coarse sandy substratum. Tinytown soils have hues of 5YR to 10R in the particle-size control section.
GEOGRAPHIC SETTING:
Landform- valley bottoms, stream terraces, alluvial fans and footslopes of escarpments
Elevation - 5,000 to 5,700 feet
Slope - 0 to 15 percent
Parent material - stratified alluvium primarily from granite or other coarse grained igneous or metamorphic rocks
Climate - long cold winters; moist springs; warm, dry summers
Mean annual precipitation - 12 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 Valleyflat and Rockerjohn series. Valleyflat soils have coarse sandy substrata within 8 to 20 inches of the surface. They occur on more linear to convex landscape positions. Rockerjohn soils have lime present in one or more subsoil horizons and have coarse sandy substrata within 9 to 23 inches of the soil surface. Rockerjohn soils tend to occur in areas containing more fine grained strata in subsoil layers between 40 to 80 inches, associated with more mixed Tertiary valley fill parent materials.
DRAINAGE AND PERMEABILITY: Well drained; moderately rapid permeability in upper horizons over rapid permeability in underlying coarse substrates.
USE AND VEGETATION: Pitchstone soils are primarily used for rangeland, wildlife habitat and urban development. Rangeland vegetation is mainly bluebunch wheatgrass, rubber rabbitbrush and Canada bluegrass with lesser amounts of needleandthread, hooded phlox, silvery lupine and other miscellaneous forbs and subshrubs.
DISTRIBUTION AND EXTENT: Pitchstone 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 (A, Bw horizons); a cambic horizon from 5 to 12 inches (Bw horizon); coarse granitic alluvium from 27 to 60 inches (C1, C2 horizons); a particle-size control section from 10 to 40 inches (Bw, BC, C1 horizons). Pitchstone soils have a frigid temperature regime and an ustic moisture regime that borders on aridic. Gravels throughout the profile are primarily fine pea gravel less than 10 mm in diameter.