LOCATION PLIMPTON MT

Established Series
Rev: KTS-JJU-RJS
06/2011

PLIMPTON SERIES

The Plimpton series consists of very deep, well drained soils that formed in mixed alluvium on fan remnants, outwash plains and alluvial fans. These soils are subject to prolonged saturation from flood irrigation. Slopes are 0 to 8 percent. Mean annual precipitation is about 16 inches, and mean annual air temperature is about 37 degrees F.

TAXONOMIC CLASS: Fine-loamy, mixed, superactive Oxyaquic Argicryolls

TYPICAL PEDON: Plimpton silt loam, in irrigated grass pasture (colors are for dry soil unless otherwise noted).

Oi--0 to 1 inch; undecomposed and partially decomposed matted roots; abrupt smooth boundary. (1 to 3 inches thick)

A1--1 to 9 inches; very dark gray (10YR 3/1) silt loam, black (10YR 2/1) moist; few fine faint dark brown (7.5YR 3/3) moist redox concentrations (due to prolonged saturation from flood irrigation); moderate medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine and fine roots; common very fine and fine dendritic tubular pores; 5 percent gravel; slightly alkaline (pH 7.6); gradual wavy boundary.

A2--9 to 19 inches; grayish brown (10YR 5/2) loam, very dark brown (10YR 2/2) moist; few fine faint dark brown (7.5YR 3/3)moist redox concentrations (due to prolonged saturation from flood irrigation); moderate medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine and fine roots; many very fine and fine dendritic tubular pores; 10 percent gravel; neutral (pH 6.8); gradual wavy boundary. (combined thickness of A1, A2 horizons - 10 to 20 inches)

Bt--19 to 38 inches; pale brown (10YR 6/3) sandy clay loam, brown (10YR 4/3) moist; few fine faint brown (7.5YR 4/3) moist redox concentrations (due to prolonged saturation from flood irrigation); moderate medium prismatic structure; hard, firm, moderately sticky and moderately plastic; common very fine and fine roots; many very fine and fine dendritic tubular pores; common distinct continuous clay films on faces of peds and common faint patchy clay films between sand grains; 10 percent gravel; neutral (pH 6.8); gradual wavy boundary. (12 to 40 inches thick)

BC--38 to 60 inches; very pale brown (10YR 8/2) gravelly sandy clay loam, light brownish gray (10YR 6/2) moist; weak fine and medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; few very fine roots; common very fine dendritic tubular pores; 20 percent gravel; neutral (pH 6.8).

TYPE LOCATION: Beaverhead County, Montana; approximately 50 feet south and 1600 feet west of the northeast corner of sec. 28, T. 1S, R. 16 W; USGS Gibbons School, Montana topographic quadrangle; NAD 83, zone 12, UTM 299011e, 5066860n.

RANGE IN CHARACTERISTICS:
Mean annual soil temperature - 35 to 40 degrees F., Cryic temperature regime.
Mean summer soil temperature - 53 to 57 degrees F.
Mollic epipedon thickness - 10 to 20 inches
Redox concentrations: Have not developed because of a fluctuating water table, but have developed from prolonged saturation from flood irrigation.

Note: Some pedons may have an E and/or Bt/E horizon.

A1, A2 horizons
Value: 3 to 5 dry; 2 or 3 moist
Chroma: 1 to 3; dry or moist
Texture: sandy clay loam, loam or silt loam
Clay content: 18 to 25 percent
Rock fragments: 5 to 15 percent gravel
Reaction: pH 6.1 to 7.6

Bt horizon
Hue: 10YR or 2.5Y; dry or moist
Value: 5 to 7 dry; 4 or 5 moist
Chroma: 3 or 4; dry or moist
Texture: sandy clay loam, loam or clay loam
Clay content: 25 to 35 percent
Rock fragments: 5 to 30 percent--5 to 25 percent gravel, 0 to 5 percent cobbles
Reaction: pH 5.8 to 7.3

BC horizon
Hue: 7.5YR, 10YR or 2.5Y; dry or moist
Value: 6 to 8 dry; 3 to 6 moist
Chroma: 2 to 6; dry or moist
Texture: sandy loam, sandy clay loam or loam
Clay content: 15 to 25 percent
Rock fragments: 15 to 50 percent--15 to 30 percent gravel, 0 to 20 percent cobbles
Reaction: pH 6.1 to 7.3

COMPETING SERIES:
Beavet (WY) - have secondary calcium carbonate accumulation
Bighole - have secondary calcium carbonate accumulation
Wallrock - have secondary calcium carbonate accumulation

GEOGRAPHIC SETTING:
Landform - fan remnants, outwash plains, and alluvial fans
Elevation - 6,000 to 7,300 feet
Slope - 0 to 8 percent.
Parent material - mixed alluvium
Climate - long, cold winters; cool, moist springs; short, cool summers.
Mean annual precipitation - 14 to 19 inches
Mean annual air temperature - 34 to 39 degrees F.
Frost-free period - 30 to 70 days

GEOGRAPHICALLY ASSOCIATED SOILS:
These are the Beaverslide, Cowcamp, Mooseflat, Shewag and Wisdom soils. The Beaverslide soils have greater than 35 percent clay in the control section and are on remnant terraces and fans, Cowcamp soils are loamy-skeletal and are on remnant terraces and fans, Mooseflat soils are very poorly drained and are on floodplains and drainageways, Shewag soils are 10 to 20 inches to sand and gravel and are on outwash plains, Wisdom soils are fine-loamy over sandy or sandy-skeletal and are on outwash plains.

DRAINAGE AND PERMEABILITY: Well drained; moderately slow permeability.

USE AND VEGETATION: Plimpton soils are used for irrigated grass hay and irrigated pasture. The vegetation is mainly Garrison creeping foxtail, meadow foxtail, timothy, tufted hairgrass, and other miscellaneous sedges, rushes and forbs.

DISTRIBUTION AND EXTENT: Plimpton soils are not extensive in the intermountain valleys of southwestern Montana. MLRA - 44B.

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

SERIES ESTABLISHED: Beaverhead County, Montana, Big Hole Valley Area, 2005.

REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon from - 1 to 19 inches (A1, A2 horizons)
Argillic horizon - from 19 to 38 inches (Bt horizon)
Redox features - from 1 to 38 inches (A1, A2, Bt horizons)
Particle-size control section - from 19 to 38 inches (Bt horizon)

Plimpton soils have a cryic temperature regime, an ustic moisture regime, and an oxyaquic moisture subclass.

National Cooperative Soil Survey
U.S.A.