LOCATION RATIOPEAK MT

Established Series
Rev. DES-JJU-EMM
03/2014

RATIOPEAK SERIES

The Ratiopeak series consists of very deep, well drained soils that formed in alluvium, slope alluvium, colluvium or slide deposits derived from fine grained sandstone or fine grained igneous rock. These soils are on alluvial fans, fan remnants, stream terraces, hills, mountain slopes, ridges and landslides. Slopes are 0 to 50 percent. Mean annual precipitation is about 16 inches, and mean annual air temperature is about 38 degrees F.

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 A1, A2 horizons - 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 faint grayish brown (10YR 5/2) clay films on faces of peds; 40 percent gravel; neutral (pH 7.2); gradual wavy boundary. (4 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;50 percent gravel and 5 percent cobbles; common fine masses and threads of calcium carbonate and common distinct calcium carbonate 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 northwest corner of sec. 3, T. 5N, R. 2W.

RANGE IN CHARACTERISTICS:
Soil temperature - 38 to 42 degrees F.
Mollic epipedon thickness - 10 to 15 inches
Depth to argillic horizon - 6 to 11 inches
Depth to the secondary calcium carbonate accumulation - 25 to 40 inches

A1, A2 horizons
Hue: 10YR, 7.5YR or 2.5Y; dry or moist
Value: 3 to 5 dry; 2 or 3 moist
Chroma: 1 to 3; dry or moist
Clay content: 18 to 27 percent
Rock fragments: 15 to 60 percent--10 to 35 percent gravel, 0 to 25 percent cobbles, 0 to 5 percent stones
Reaction: pH 6.1 to 7.3

Bt1, Bt2, Bt3 horizons
Hue: 7.5YR, 10YR or 2.5Y; dry or moist
Value: 4 to 6 dry; 3 to 5 moist
Chroma: 2 to 6; dry or moist
Texture: loam, clay loam or sandy clay loam
Clay content: 25 to 35 percent
Rock fragments: 35 to 70 percent--25 to 45 percent gravel, 0 to 30 percent cobbles, 0 to 5 percent stones
Reaction: pH 6.1 to 7.8

Bk horizon
Hue: 7.5YR, 10YR or 2.5Y; dry or moist
Value: 6 or 7 dry; 5 or 6 moist
Chroma: 2 to 4; dry or moist
Texture: loam, clay loam or sandy loam
Clay content: 15 to 30 percent
Rock fragments: 35 to 70 percent--20 to 60 percent gravel, 5 to 40 percent cobbles, 0 to 5 percent stones
Calcium carbonate equivalent: 5 to 15 percent
Reaction: pH 7.4 to 8.4

COMPETING SERIES:
Anniesdraw (WY) - have a lithologic discontinuity
Bassel (CO) - are deep to a paralithic contact
Blaine (MT) - are moderately deep to a lithic contact
Bowen (CO) - are moderately deep to a lithic contact
Fingerrock (CO) - do not have secondary calcium carbonate accumulation
Fornor (WY) - have secondary carbonate accumulation at depths of less than 25 inches
Fourmile (CO) - have a lithologic discontinuity
Geertsen (UT) - are deep to a lithic contact
Hoodle (UT) - have a calcic horizon
Hungryhill (MT) - are moderately deep to a lithic contact
Lagarita (CO) - have a calcic horizon
Lambe (CO) - have an argillic horizon greater than 37 inches thick
Libeg (MT) - do not have secondary calcium carbonate accumulation
Nathale (WY) - are moderately deep to a lithic contact
Nathrop (CO) - are moderately deep to a lithic contact
Norriston (CO) - do not have secondary calcium carbonate accumulation
Quander (CO) - do not have secondary calcium carbonate accumulation
Silverheels (CO) - do not have secondary calcium carbonate accumulation
Spanpeak (MT) - do not have secondary calcium carbonate accumulation
Woodhall (CO) - are moderately deep to a lithic contact

GEOGRAPHIC SETTING:
Landform - alluvial fans, fan remnants, stream terraces, hills, mountain slopes, ridges and landslides
Elevation - 5,500 to 8,000 feet
Slope - 0 to 50 percent
Parent material - alluvium, slope alluvium, colluvium or slide deposits derived from 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. MLRAs - 43B, 44B and 46.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana.

SERIES ESTABLISHED: Jefferson County, Montana, 1998.

REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - from 0 to 15 inches (A1, A2, Bt1 horizons)
Argillic horizon - from 10 to 35 inches (Bt1, Bt2, Bt3 horizons)
Secondary calcium carbonate accumulation - from 35 to 60 inches (Bk horizon)
Particle-size control section - from 10 to 30 inches (Bt1, Bt2, part of Bt3 horizons)

Ratiopeak soils have a cryic temperature regime and an ustic moisture regime.

ADDITIONAL DATA: Soil interpretation record - MT3038.

National Cooperative Soil Survey
U.S.A.