LOCATION THREERIV                MT

Established Series
Rev. GAR-JJU-RJS
06/2011

THREERIV SERIES

The Threeriv series consists of very deep, very poorly drained soils that formed in alluvium. These soils are on flood plains. Slopes are 0 to 2 percent. Mean annual precipitation is about 15 inches, and the mean annual air temperature is about 40 degrees F.

TAXONOMIC CLASS: Fine-loamy over sandy or sandy-skeletal, mixed, superactive, calcareous, frigid Typic Fluvaquents

TYPICAL PEDON: Threeriv loam, in pastureland (colors are for moist soil unless otherwise noted).

Oe--0 to 4 inches; partially decomposed sedges, rushes and grasses; slightly alkaline (pH 7.8); clear smooth boundary. (2 to 6 inches thick)

Ag--4 to 9 inches; dark gray (10YR 4/1) loam, gray (10YR 5/1) dry; few fine prominent brown (7.5YR 4/4) redox concentrations; weak medium subangular blocky structure; hard, friable, moderately sticky and moderately plastic; few very fine and fine, and common medium roots; 10 percent gravel; strongly effervescent; moderately alkaline (pH 8.0). (2 to 9 inches thick)

Cg--9 to 29 inches; light brownish gray (10YR 6/2) sandy clay loam consisting of strata of sandy clay loam and sandy loam, light gray (10YR 7/2) dry; common fine prominent dark yellowish brown (10YR 4/6) redox concentrations; massive; hard, friable, slightly sticky and slightly plastic; few very fine, fine and medium roots; 10 percent gravel; violently effervescent; moderately alkaline (pH 8.4); clear smooth boundary. (15 to 31 inches thick)

2C--29 to 60 inches; variegated extremely gravelly loamy sand; single grain; loose, nonsticky and nonplastic; 60 percent gravel and 15 percent cobbles; moderately alkaline (pH 8.0).

TYPE LOCATION: Gallatin County, Montana; 2,200 feet south and 200 feet west of the northeast corner of sec. 2, T. 1N, R. 1E.

RANGE IN CHARACTERISTICS:
Mean annual soil temperature - 40 to 45 degrees F.
Depth to lithologic discontinuity - 20 to 40 inches
Depth to seasonal high water table - 0 to 12 inches

Ag horizon
Hue: 10YR, N, 5Y; dry or moist
Value: 5 or 6 dry; 3 or 4 moist
Texture: loam, silt loam or silty clay loam
Clay content: 18 to 35 percent
Rock fragments: 0 to 10 percent gravel
Calcium carbonate equivalent: 2 to 15 percent
Reaction: pH 7.9 to 8.4

Cg horizon
Hue: 10YR, 5Y or 2.5Y; dry or moist
Value: 5 to 7 dry; 4 to 6 moist
Chroma: 1 or 2; dry or moist
Texture: stratified sandy clay loam, sandy loam, silty clay loam or clay loam
Clay content: 15 to 35 percent
Rock fragments: 0 to 10 percent gravel
Calcium carbonate equivalent: 2 to 15 percent
Reaction: pH 7.9 to 8.4

2C horizon
Hue: 10YR or variegated; dry or moist
Value: 5 or 6 dry; 4 or 5 moist
Texture: loamy sand, loamy coarse sand, sand or coarse sand
Clay content: 0 to 10 percent
Rock fragments: 35 to 85 percent-- 25 to 60 percent gravel, 10 to 25 percent cobbles
Reaction: pH 7.4 to 8.4

COMPETING SERIES:
Beavrock (MT) - have a seasonal high water table at 12 to 24 inches

GEOGRAPHIC SETTING:
Landform - flood plains
Elevation - 4,000 to 6,500 feet
Slope - 0 to 2 percent
Parent material - alluvium
Climate - long, cold winters; moist springs; warm summers
Mean annual precipitation - 10 to 18 inches
Mean annual air temperature - 38 to 43 degrees F.
Frost-free period - 70 to 110 days

GEOGRAPHICALLY ASSOCIATED SOILS: None listed.

DRAINAGE AND PERMEABILITY: Very poorly drained; moderately slow over rapid permeability.

USE AND VEGETATION: Threeriv soils are used mainly for pasture and wildlife habitat. Potential native vegetation may include tall reedgrasses, tall sedges and rushes, American sloughgrass, iris, willows, waterbirch, dogwood and silver buffaloberry, as well as other forbs, grasses, sedges and shrubs.

DISTRIBUTION AND EXTENT: Threeriv soils are of small extent in Southwestern Montana. MLRA - 44B.

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

SERIES ESTABLISHED: Gallatin County, Montana, 1997.

REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - from 0 to 9 inches (Oe, Ag horizons)
Lithologic discontinuity - at 29 inches (2C horizon)
Particle-size control section - from 14 to 44 inches (part of Cg, part of 2C horizons)

Threeriv soils have a frigid temperature regime and an aquic moisture regime.

ADDITIONAL DATA: Soil interpretation record - MT1640.

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National Cooperative Soil Survey
U.S.A.