LOCATION RATIOPEAK MTEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive Ustic Argicryolls
TYPICAL PEDON: Ratiopeak gravelly loam, bouldery, in rangeland (colors are for dry soil unless otherwise noted).
A1--0 to 3 inches; very dark grayish brown (10YR 3/2) gravelly loam, black (10YR 2/1) moist; moderate fine subangular blocky structure; slightly hard, very friable, slightly sticky and nonplastic; many very fine and fine roots; many very fine and fine interstitial pores; 20 percent gravel; slightly acid (pH 6.4); clear wavy boundary.
A2--3 to 10 inches; very dark grayish brown (10YR 3/2) gravelly loam, very dark brown (10YR 2/2) moist; strong medium subangular blocky structure; slightly hard, very friable, slightly sticky and nonplastic; many very fine and fine roots; many very fine and fine interstitial and tubular pores; 25 percent gravel; neutral (pH 6.6); clear wavy boundary. (Combined thickness of A horizons is 6 to 12 inches).
Bt1--10 to 15 inches; brown (10YR 4/3) very gravelly clay loam, dark brown (10YR 3/3) moist; strong medium prismatic structure parting to moderate medium subangular blocky; slightly hard, friable, slightly sticky and slightly plastic; many very fine and fine roots; many very fine and fine and few medium pores; common faint dark grayish brown (10YR 4/2) clay films on faces of peds; 40 percent gravel; neutral (pH 7.0); gradual wavy boundary. (4 to 10 inches thick)
Bt2--15 to 26 inches; pale brown (10YR 6/3) very gravelly clay loam, brown (10YR 5/3) moist; strong medium prismatic structure parting to moderate medium subangular blocky; hard, firm, moderately sticky and moderately plastic; many very fine and fine and few medium roots; many very fine and fine interstitial and tubular pores; common distinct grayish brown (10YR 5/2) clay films on faces of peds; 40 percent gravel; neutral (pH 7.2); gradual wavy boundary. (10 to 15 inches thick)
Bt3--26 to 35 inches; pale brown (10YR 6/3) very gravelly loam, brown (10YR 5/3) moist; moderate coarse prismatic structure; hard, firm, moderately sticky and moderately plastic; common very fine and fine roots; common very fine and fine, and few medium pores; few distinct clay films on faces of peds; 45 percent gravel; slightly alkaline (pH 7.8); gradual smooth boundary. (0 to 12 inches thick)
Bk--35 to 60 inches; very pale brown (10YR 7/3) very gravelly loam, yellowish brown (10YR 5/4) moist; weak medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; few very fine and fine roots; common very fine and fine interstitial and tubular pores; 5 percent cobbles, 50 percent gravel; common fine masses and threads of lime, common distinct lime casts on undersides of fragments; strongly effervescent; moderately alkaline (pH 8.3).
TYPE LOCATION: Jefferson County, Montana; 1,650 feet south and 1,000 feet east of the NW corner of sec. 3, T. 5 N., R. 2 W.
RANGE IN CHARACTERISTICS:
Soil temperature - 38 to 42 degrees F.
Moisture control section - between 4 and 12 inches.
Mollic epipedon thickness - 10 to 15 inches.
Depth to argillic horizon - 6 to 11 inches.
Depth to the Bk horizon - 25 to 40 inches.
Surface stones and boulders - 0 to 3 percent
A horizons - Hue: 10YR, 7.5YR, or 2.5Y
Value: 3, 4 or 5 dry; 2 or 3 moist
Chroma: 1, 2 or 3
Clay content: 18 to 27 percent
Rock fragments: 15 to 60 percent--0 to 5 percent stones, 0 to 25 percent cobbles, 15 to 35 percent gravel
Reaction: pH 6.1 to 7.3
Bt horizons - Hue: 7.5YR, 10YR or 2.5Y
Value: 4, 5, or 6 dry; 3, 4, or 5 moist
Chroma: 2, 3, 4, 5, or 6
Texture: loam, clay loam or sandy clay loam
Clay content: 25 to 35 percent
Rock fragments: 35 to 70 percent--0 to 5 percent stones, 0 to 30 percent cobbles, and 35 to 45 percent gravel
Reaction: pH 6.1 to 7.8
Bk horizon - Hue: 7.5YR, 10YR or 2.5Y
Value: 6 or 7 dry; 5 or 6 moist
Chroma: 2, 3 or 4
Texture: loam, clay loam or sandy loam
Clay content: 15 to 30 percent
Rock fragments: 35 to 70 percent--0 to 5 percent stones, 5 to 40 percent cobbles, and 20 to 50 percent gravel
Calcium carbonate equivalent: 5 to 15 percent
Reaction: pH 7.4 to 8.4
COMPETING SERIES:
Blaine (MT) - has a lithic contact at depths of 40 inches or less.
Bowen (CO) - has a lithic contact of schist or micaceous gneiss at depths of 40 inches or less.
Fingerrock (CO) does not have a horizon of secondary carbonate accumulation.
Fornor (WY) - the horizon of secondary carbonate accumulation is above a depth of 25 inches; argillic horizon is less than 15 inches thick.
Fourmile (CO) - has a sandy-skeletal horizon of very gravelly coarse sand or coarse loamy sand above a depth of 40 inches.
Geertsen (UT) - calcareous in the argillic horizon; has a lithic contact of limestone above a depth of 60 inches.
Hodden (CO) - argillic horizon is less than 10 inches thick; has a calcic horizon; is sandy-skeletal below 40 inches.
Hoodle (UT) - has a calcic horizon that is weakly cemented.
Lagarita (CO) - has a calcic horizon.
Libeg (MT) - does not have a horizon of secondary carbonate accumulation.
Maciver (MT) - has a calcic horizon, has secondary calcium carbonate accumulation above a depth of 24 inches.
Nathale (WY) - has a lithic contact at depths of 40 inches or less.
Nathrop (CO) - has a lithic contact of limestone at depths of 40 inches or less.
Norriston (CO) - has sandy-skeletal materials above a depth of 40 inches.
Quander (CO) - does not have a horizon of secondary carbonate accumulation.
Spanpeak (MT) - does not have a horizon of secondary carbonate accumulation.
Teeler (WY) - has a horizon of carbonate accumulation above a depth of 25 inches; has an argillic horizon 5 to 10 inches thick.
Woodhall (CO) - has a lithic contact at depths of 40 inches or less.
GEOGRAPHIC SETTING:
Landform - alluvial fans, hills and sideslopes of mountains.
Elevation - 5,500 to 8,000 feet.
Slope 0 to 45 percent.
Parent material - alluvium or colluvium derived from hard fine grained sandstone or fine grained igneous rock.
Climate - long, cold winters; cool, moist springs; short, cool summers.
Mean annual precipitation - 14 to 24 inches.
Mean annual air temperature - 34 to 40 degrees F.
Frost-free period - 30 to 70 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Cheadle and Tiban soils. Cheadle soils are shallow, do not have an argillic horizon and are on more convex postions. Tiban soils do not have an argillic horizon and are on similar landform positions.
DRAINAGE AND PERMEABILITY: Well drained, moderately slow permeability.
USE AND VEGETATION: Ratiopeak soils are primarily used for rangeland. The potential native vegetation is mainly bluebunch wheatgrass, Idaho fescue, Columbia needlegrass, rough fescue, yarrow, lupine, mountain big sagebrush, and stoneseed. Some areas have widely spaced Douglas fir and Rocky Mountain juniper.
DISTRIBUTION AND EXTENT: Ratiopeak soils are of moderate extent in southwestern Montana.
MLRA OFFICE RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Jefferson County, Montana, 1998.
REMARKS: Soil interpretation record: MT3038. Diagnostic horizons and features recognized in this pedon are: a mollic epipedon from the surface to 15 inches (A1, A2, Bt1 horizons); an argillic horizon from 10 to 35 inches (Bt1, Bt2, Bt3 horizons); a particle-size control section from 10 to 30 inches (Bt1, Bt2, Bt3 horizons); a horizon of secondary calcium carbonate accumulation from 35 to 60 inches (Bk horizon). Ratiopeak soils have a cryic temperature regime and an ustic moisture regime.