LOCATION ROCKERJOHN MTEstablished Series
TAXONOMIC CLASS: Sandy, mixed, frigid Aridic Haplustolls
TYPICAL PEDON: Rockerjohn sandy loam, in grassland (colors are for dry soil unless otherwise noted).
A1--0 to 2 inches; grayish brown (10YR 5/2) sandy loam, very dark brown (10YR 2/2) moist; moderate very fine granular structure; soft, very friable, non-sticky and slightly plastic; many very fine and few fine and medium roots; few very fine tubular pores; 2 percent fine subangular gravel; moderately acid (pH 5.8); clear smooth boundary.
A2--2 to 5 inches; grayish brown (10YR 5/2) sandy loam, very dark brown (10YR 2/2) moist; weak fine granular structure; soft, very friable, slightly sticky and slightly plastic; many very fine and few fine and medium roots; few very fine tubular pores; 2 percent fine subangular gravel; neutral (pH 6.6); clear smooth boundary. (combined thickness of A horizons 4 to 8 inches)
Bw--5 to 14 inches; light yellowish brown (10YR 6/4) coarse sandy loam, dark yellowish brown (10YR 4/4) moist; moderate medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine and few fine and medium roots; few fine and very fine tubular pores; 10 percent fine subangular gravel; neutral (pH 7.0); clear smooth boundary. (6 to 15 inches thick)
2C--14 to 38 inches; variegated, mainly light gray (10YR 7/2) and light yellowish brown (10YR 6/4)gravelly coarse sand, mainly pale brown (10YR 6/3) moist; single grain; loose, non-sticky and non-plastic; few very fine roots; many fine and very fine, and common medium interstitial pores; 30 percent fine subangular gravel; slightly alkaline (pH 7.6); abrupt smooth boundary. (15 to 40 inches thick)
3Ck--38 to 46 inches; pale brown (10YR 6/3) sandy loam, brown (10YR 4/3) moist; massive; slightly hard, friable, slightly sticky and slightly plastic; few very fine tubular pores; 5 percent fine subangular gravel; common fine seams and threads of secondary lime; strongly effervescent; moderately alkaline (pH 8.0); clear smooth boundary. (0 to 36 inches thick)
4C--46 to 72 inches; pale brown (10YR 6/3) gravelly loamy sand, brown (10YR 4/3) moist; single grain; loose, non-sticky and non-plastic; many fine and very fine interstitial pores; 20 percent fine subangular gravel; slightly alkaline (pH 7.4).
TYPE LOCATION: Silver Bow County, Montana; 900 feet east and 1300 feet north of the SW corner of sec. 16, T. 2 N., R. 7 W. Homestake topographic quadrangle, UTM zone 12T, 0385031E, 5086041N, NAD 27
RANGE IN CHARACTERISTICS:
Mean annual soil temperature - 40 to 46 degrees F., frigid temperature regime.
Soil moisture control section - 12 to 36 inches; dry between four tenths and six 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 that borders on aridic.
Thickness of mollic epipedon - 7 to 15 inches, mixed
Depth to secondary lime - 19 to 56 inches
Phases - sandy substratum
A Horizons
Value: 4 or 5 dry; 2 or 3 moist
Chroma: 2 or 3
Texture: sandy loam, coarse sandy loam or loam
Clay content: 8 to 18 percent
Rock fragments: 2 to 55 percent, mainly fine gravel
Reaction: pH 5.4 to 7.2
Bw Horizon
Value: 4, 5, or 6 dry; 3, 4, or 5 moist
Chroma: 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 6.2 to 7.4
2C and 4C Horizons
Hue: 10YR, 2.5Y, or 7.5YR
Value: 5, 6, or 7 dry; 4, 5, or 6 moist
Chroma: 2, 3, or 4
Texture: coarse sand, loamy coarse sand or loamy sand
Clay content: 0 to 8 percent
Rock fragments: 5 to 35 percent, mainly fine gravel
Calcium carbonate equivalent: 0 to 5 percent
Reaction: pH 6.8 to 8.4
Note: textures are often stratified in these horizons
3Ck Horizon Hue: 10YR or 7.5YR
Value: 5, 6, or 7 dry; 4, 5, or 6 moist
Chroma: 2, 3, or 4
Texture: sandy loam, coarse sandy loam, loam or sandy clay loam; interspersed, thin strata of coarse sand common
Clay content: 10 to 22 percent
Rock fragments: 5 to 20 percent, mainly fine gravel
Calcium carbonate equivalent: 1 to 5 percent
Reaction: pH 7.8 to 8.4
Note: This horizon is lacking in the sandy substratum phase of Rockerjohn soils and is replaced by a 2Ck horizon.
COMPETING SERIES: These are the Ouray and Valleyflat series. Ouray soils have less than 15 percent rock fragments throughout the profile and do not have a Bw horizon. Valleyflat soils do not have secondary carbonates in the subsoil.
GEOGRAPHIC SETTING:
Landform- valley floor, alluvial fans, stream terraces, hills, mountains
Elevation 4,760 to 6,970 feet
Slope - 0 to 30 percent
Parent material - alluvium from mixed sources but with a strong influence from granite or other coarse grained igneous or metamorphic rocks
Climate - long cold winters; moist springs; warm, dry summers
Mean annual precipitation - 10 to 14 inches
Mean annual air temperature - 40 to 43 degrees F.
Frost-free period - 70 to 100 days
GEOGRAPHICALLY ASSOCIATED SOILS:
These are the Pitchstone series and the competing Valleyflat series. Pitchstone soils are deeper than 25 inches to coarse sandy substrates and occur in swales, at the base of escarpments or other more depositional positions. Valleyflat soils do not have substrata with accumulated calcium carbonate and occur in areas with more consistently coarse, sandy substrates.
DRAINAGE AND PERMEABILITY: Well drained; moderately rapid permeability.
USE AND VEGETATION: Rockerjohn soils are primarily used for rangeland and suburban development. The native vegetation is mainly bluebunch wheatgrass, rubber rabbitbrush, Canada bluegrass, fringed sagewort, needleandthread, silvery lupine, hairy false goldenaster and spiny phlox.
DISTRIBUTION AND EXTENT: Rockerjohn soils are of limited extent in intermountain valleys of southwestern Montana. MLRA 44.
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, part of the Bw horizon); a cambic horizon from 5 to 14 inches (Bw horizon); sandy substrata from 14 to 38 and 46 to 72 inches (2C and 4C horizons); a horizon of accumulated secondary lime from 38 to 46 inches (3Ck horizon); a particle-size control section from 10 to 40 inches (part of the Bw, 2C, and part of the 3Ck horizon). Rockerjohn soils have a frigid temperature regime and an ustic soil moisture regime that borders on aridic. Gravel throughout the profile are primarily fine pea gravel less than 7 mm in diameter.