LOCATION SHAWMUT MT

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

SHAWMUT SERIES

The Shawmut series consists of very deep, well drained soils that formed in gravelly alluvium, glaciofluvial deposits, colluvium, or till. These soils are on plains, alluvial fans, stream terraces, escarpments, hills, mountains, and moraines. Slopes are 0 to 60 percent. Mean annual precipitation is about 16 inches, and mean annual temperature is about 46 degrees F.

TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, frigid Typic Argiustolls

TYPICAL PEDON: Shawmut gravelly loam, in grassland (colors are for dry soil unless otherwise noted).

A--0 to 3 inches; brown (10YR 4/3) gravelly loam, dark brown (10YR 3/3) moist; moderate fine granular structure, weak thin platy in upper inch; slightly hard, very friable, slightly sticky and slightly plastic; many fine roots; about 15 percent gravel and 5 percent cobbles; neutral (pH 7.0); clear wavy boundary. (3 to 8 inches thick)

Bt1--3 to 9 inches; dark grayish brown (10YR 4/2) gravelly clay loam, very dark grayish brown (10YR 3/2) moist; weak fine prismatic structure parting to strong fine angular and subangular blocky; hard, very friable, moderately sticky and moderately plastic; many fine roots; common fine pores; common faint clay films on faces of peds and on gravel; 25 percent gravel, 5 percent cobbles; neutral (pH 7.0); clear boundary.

Bt2--9 to 12 inches; dark grayish brown (10YR 4/2) very gravelly clay loam, very dark grayish brown (10YR 3/2) moist; strong fine blocky structure; hard, very friable, moderately sticky and moderately plastic; many fine and very fine roots; common fine pores; many distinct clay films on faces of peds and on gravel; 35 percent gravel, 5 percent cobbles; slightly alkaline (pH 7.8); clear wavy boundary. (Combined thickness of Bt horizons is 6 to 14 inches.)

Btk--12 to 15 inches; grayish brown (10YR 5/2) very gravelly clay loam, dark grayish brown (10YR 4/2) moist; moderate medium and fine blocky structure; hard, very friable, moderately sticky and moderately plastic; many fine roots; common fine pores; common faint clay films on faces of peds; 50 percent gravel, 5 percent cobbles; common distinct lime coats on underside of coarse fragments; strongly effervescent; moderately alkaline (pH 8.2); clear wavy boundary. (0 to 9 inches thick)

Bk1--15 to 24 inches; grayish brown (2.5Y 5/2) very gravelly loam, dark grayish brown (2.5Y 4/2) moist; massive; slightly hard, very friable, slightly sticky and slightly plastic; common fine roots; 50 percent gravel, 5 percent cobbles; many distinct lime coats on underside of coarse fragments; strongly effervescent; moderately alkaline (pH 8.2); gradual smooth boundary. (8 to 15 inches thick)

Bk2--24 to 60 inches; grayish brown (2.5Y 5/2) extremely gravelly loam, dark grayish brown (2.5Y 4/2) moist; massive; slightly hard, very friable, slightly sticky and slightly plastic; many distinct lime coats on underside of gravel; strongly effervescent; moderately alkaline (pH 8.4).

TYPE LOCATION: Blaine County, Montana; about 1,300 feet north and 1,000 feet east of the SW corner of sec. 15, T. 29 N., R. 21 E.

RANGE IN CHARACTERISTICS:

Soil temperature - 38 to 47 degrees F.
Moisture control section - between 4 and 12 inches.
Mollic epipedon thickness - 7 to 16 inches.
Depth to calcic horizon - 9 to 20 inches.
Surface stones or boulders - 0 to 3 percent

A horizon
Hue: 7.5YR, 10YR or 2.5Y
Value: 3, 4 or 5 dry, 2 or 3 moist
Chroma: 2 or 3 dry or moist
Texture: loam, silt loam, sandy clay loam or sandy loam
Clay content: 15 to 27 percent
Rock fragments: 0 to 80 percent--0 to 40 percent stones and boulders, 0 to 25 percent cobbles, 0 to 50 percent gravel
Reaction: pH 6.1 to 7.8

Bt1 horizon
Hue: 7.5YR, 10YR or 2.5Y
Value: 3, 4, 5 or 6 dry; 2, 3 or 4 moist
Chroma: 2 or 3
Texture: sandy clay loam or clay loam
Clay content: 20 to 35 percent
Rock fragments: 15 to 80 percent--0 to 15 percent stones, 0 to 20 percent cobbles, 15 to 45 percent gravel
Reaction: pH 6.6 to 7.8

Bt2 horizon
Hue: 7.5YR, 10YR or 2.5Y
Value: 3, 4, 5 or 6 dry; 2, 3, or 4 moist
Chroma: 2, 3 or 4 dry or moist
Texture: sandy clay loam or clay loam
Clay content: 20 to 35 percent
Rock fragments: 35 to 80 percent--0 to 15 percent stones, 0 to 20 percent cobbles, 30 to 60 percent gravel
Reaction: pH 6.6 to 8.4

Btk horizon
Hue: 7.5YR or 10YR
Value: 3, 4, 5, or 6 dry; 2, 3, 4, or 5 moist
Chroma: 2, 3 or 4 dry or moist
Texture: clay loam, loam, sandy clay loam or sandy loam
Clay content: 18 to 35 percent
Rock fragments: 35 to 80 percent--0 to 20 percent stones, 0 to 20 percent cobbles, 30 to 60 percent gravel
Calcium carbonate equivalent: 15 to 30 percent
Reaction: pH 7.9 to 8.4

Bk1 horizon
Hue: 2.5Y or 10YR
Value: 5, 6, or 7 dry; 4, 5, or 6 moist
Chroma: 2, 3 or 4
Texture: sandy loam, sandy clay loam, clay loam, or loam
Clay content: 15 to 30 percent
Rock fragments: 35 to 80 percent--0 to 20 percent stones, 0 to 20 percent cobbles, 30 to 75 percent gravel
Calcium carbonate equivalent: 15 to 30 percent
Reaction: pH 7.9 to 8.4

Bk2 horizon
Hue: 2.5Y or 10YR
Value: 5, 6, 7, or 8 dry, 4, 5, 6, or 7 moist
Chroma: 2, 3 or 4 dry or moist
Texture: sandy loam, sandy clay loam or loam
Clay content: 5 to 30 percent
Rock fragments: 50 to 85 percent--0 to 20 percent stones, 0 to 20 percent cobbles, 35 to 70 percent gravel
Calcium carbonate equivalent: 10 to 25 percent
Electrical conductivity: less than 2 mmhos/cm
Reaction: pH 7.9 to 9.0

COMPETING SERIES:
Averett (UT) - has a lithic contact at a depth of 60 to 80 inches.

Bendire (CO) - has a lithic contact at a depth of 20 to 40 inches.

Blaincreek (MT) - has a lithic contact at a depth of 20 to 40 inches.

Borpark (CO) - calcareous throughout the soil; has 5 percent calcium carbonate accumulation in the surface and argillic horizon.

Crackerville (MT) - has a paralithic contact at 20 to 38 inches.

Crampton (MT) - has a paralithic contact at 20 to 40 inches and a lithic contact at 40 to 60 inches.

Curecanti (CO) - does not have a horizon of secondary carbonate accumulations; does not have carbonates above a depth of 40 inches.

ESS (AZ) - does not have horizons of secondary carbonate accumulation.

Hilger (MT) - has more than 35 percent stones, cobbles, and boulders in the argillic horizon; does not have Btk horizons.

Holter (MT) - does not have a calcic horizon.

Quinncreek (MT) - has a lithic contact of shale at a depth of 20 to 40
inches.

Sawbuck (MT) - does not have a horizon of secondary carbonate accumulation.

Sawicki (MT) - does not have horizons of secondary carbonate accumulation.

Wickes (MT) - has a lithic contact of igneous rock at depths of 20 to 40 inches.

GEOGRAPHIC SETTING:

Landform - plains, alluvial fans, stream terraces, escarpments, hills, mountains, and moraines.
Elevation - 2,400 to 6,900 feet.
Slope - 0 to 60 percent.
Parent material - gravelly alluvium, glaciofluvial deposits, colluvium, or till from mixed sources.
Climate - long, cold winters; moist springs; warm summers.
Mean annual precipitation - 14 to 22 inches.
Mean annual temperature - 38 to 45 degrees F.
Frost-free period - 70 to 125 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Bearpaw, Roy, Williams, and the competing Hilger soils. Bearpaw and Williams soils are on till plains and contain less than 35 percent rock fragments. Roy soils are clayey-skeletal and on similar landform positions. Hilger soils are on fans and footslopes.

DRAINAGE AND PERMEABILITY: Well drained; moderate permeability.

USE AND VEGETATION: Shawmut soils are mainly used for rangeland and dryland crops. The potential native vegetation is mainly bluebunch wheatgrass, rough fescue, green needlegrass, prairie junegrass, needleandthread, forbs, and shrubs.

DISTRIBUTION AND EXTENT: Shawmut soils are extensive mainly in the central part of Montana. MLRAs 43B, 44B, and 46.

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

SERIES ESTABLISHED: Blaine County, Montana, 1976.

REMARKS: Soil interpretation records: MT0287, MT0747, MT8034, MT8042, MT1066.

Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - the zone from the soil surface to 12 inches (A, Bt1, Bt2 horizons);
Argillic horizon - the zone from 3 to 15 inches (Bt1, Bt2, Btk horizons);
Particle-size control section - the zone from 3 to 15 inches (Bt1, Bt2, Btk horizons).

Shawmut soils have an ustic moisture regime and a frigid temperature regime.

National Cooperative Soil Survey
U.S.A.