LOCATION GREGSON                 MT

Established Series
Rev. BDD-JAL-RJS
10/2012

GREGSON SERIES

The Gregson series consists of very deep, somewhat poorly drained soils that formed in alluvium or outwash. These soils are on outwash plains, outwash fans, stream terraces, alluvial fans, drainageways, depressions and flood plains. Slopes are 0 to 4 percent. Mean annual precipitation is about 380 mm, and mean annual air temperature is about 5.5 degrees C.

TAXONOMIC CLASS: Fine-loamy over sandy or sandy-skeletal, mixed, superactive, frigid Aquic Haplustolls

TYPICAL PEDON: Gregson loam, cultivated (colors are for dry soil unless otherwise noted).

Oi--0 to 3 cm; partially decomposed organic matter. (0 to 5 cm thick)

A--3 to 23 cm; very dark grayish brown (10YR 3/2) loam, black (10YR 2/1) moist; strong fine granular structure; slightly hard, friable, slightly sticky and slightly plastic; many fine and very fine roots; many fine and very fine pores; neutral (pH 7.2); clear smooth boundary. (18 to 28 cm thick)

Bw1--23 to 48 cm; light gray (10YR 7/2) loam, grayish brown (10YR 5/2) moist; moderate fine granular structure; slightly hard, very friable; slightly sticky and slightly plastic; common fine and very fine roots; many fine and very fine pores; neutral (pH 7.2); clear smooth boundary.

Bw2--48 to 58 cm; light gray (10YR 7/2) loam, grayish brown (10YR 5/2) moist; few fine faint strong brown (7.5YR 4/6) redox concentrations; moderate fine granular structure; slightly hard, very friable, slightly sticky and slightly plastic; common fine and very fine roots; many fine and very fine pores; neutral (pH 7.2) clear smooth boundary. (combined thickness of Bw horizons - 33 to 75 cm)

2C--58 to 152 cm; light gray (10YR 7/1) very gravelly loamy sand, grayish brown (10YR 5/2) moist; single grain; loose, nonsticky and nonplastic; few fine and very fine roots; common very fine pores; 10 percent cobbles and 40 percent gravel; neutral (pH 7.2).

TYPE LOCATION: Powell County, Montana; 670 feet east and 122 feet south of the NW corner of sec. 16, T. 6N., R. 9W.

RANGE IN CHARACTERISTICS:
Soil temperature - 5.0 to 8.0 degrees C.
Mollic epipedon thickness - 18 to 38 cm
Depth to a seasonal high water table - 60 to 100 cm
Depth to sand and gravel - 50 to 100 cm

A horizon
Value: 3 to 5 dry; 2 or 3 moist
Chroma: 1 or 2; dry or moist
Texture: loam, silt loam or fine sandy loam
Clay content: 18 to 27 percent
Rock fragments: 0 to 20 percent--0 to 20 percent gravel, 0 to 5 percent cobbles
Reaction: pH 6.6 to 7.8

Bw horizons
Value: 6 or 7 dry; 4 to 6 moist
Chroma: 2 or 3; dry or moist
Texture: fine sandy loam, loam or clay loam
Clay content: 18 to 35 percent
Rock fragments: 0 to 15 percent--0 to 10 percent gravel, 0 to 5 percent cobbles
Reaction: pH 6.6 to 7.8

2C horizon
Value: 6 or 7 dry; 5 or 6 moist
Chroma: 1 to 4; dry or moist
Texture: loamy sand or sand
Clay content: 0 to 8 percent
Rock fragments: 35 to 75 percent--25 to 45 percent gravel, 5 to 30 percent cobbles
Reaction: pH 6.6 to 7.8

COMPETING SERIES:
There are no competing series.

GEOGRAPHIC SETTING:
Landform - outwash plains, outwash fans, stream terraces, alluvial fans, drainageways, depressions and flood plains
Elevation - 1,200 to 1,825 meters
Slope - 0 to 4 percent
Parent material - alluvium or outwash
Mean annual precipitation - 250 to 500 mm
Mean annual temperature - 4.0 to 7.5 degrees C.
Frost-free season - 70 to 105 days

GEOGRAPHICALLY ASSOCIATED SOILS: None listed.

DRAINAGE AND PERMEABILITY: Somewhat poorly drained; permeability is moderate to the 2C horizon and rapid below.

USE AND VEGETATION: These soils are used as pasture land and hayland. The potential native vegetation is mainly tall reedgrass, tufted hairgrass, prairie cordgrass, basin wildrye, and sedges.

DISTRIBUTION AND EXTENT: Gregson soils are inextensive in southwestern Montana. MLRAs - 44A, 44B.

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

SERIES ESTABLISHED: Powell County, Montana, 1995.

REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - 3 to 23 cm (A horizon)
Cambic horizon - from 23 to 58 cm (Bw1, Bw2 horizons)
Lithologic discontinuity at 58 cm (2C horizon)
Particle-size control section - 28 to 103 cm (part of Bw1, Bw2, part of 2C horizons)

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

ADDITIONAL DATA: Laboratory data S91MT-039-1030; Soil interpretation record - MT1242.

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National Cooperative Soil Survey
U.S.A.