LOCATION BIGHOLE MT
Established Series
Rev: GFB-KTS-RJS
03/2012
BIGHOLE SERIES
The Bighole series consists of very deep, well drained soils that formed in mixed alluvium on fan remnants, stream terraces and outwash plains. The oxyaquic feature associated with this soil is a result of prolonged saturation from flood irrigation. Slopes are 0 to 4 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: Bighole silt loam, in irrigated grass hay (colors are for dry soil unless otherwise noted).
Oi--0 to 2 inches; undecomposed and partially decomposed matted roots; abrupt smooth boundary. (1 to 3 inches thick)
A1--2 to 8 inches; grayish brown (10YR 5/2) silt loam, very dark gray (10YR 3/1) moist; weak medium and fine subangular blocky structure parting to weak fine and very fine granular; soft, very friable, slightly sticky and slightly plastic; many very fine and few fine roots; many fine and very fine dendritic tubular pores; 10 percent gravel; neutral (pH 6.7); clear wavy boundary.
A2--8 to 17 inches; brown (10YR 5/3) silt loam, dark brown (10YR 3/3) moist; weak medium and fine subangular blocky structure parting to weak fine and very fine granular; soft, very friable, slightly sticky and slightly plastic; many very fine and few fine roots; many fine and very fine dendritic tubular pores; 10 percent gravel; neutral (pH 6.8); clear wavy boundary. (Combined thickness of A horizons is 10 to 15 inches)
Bt/E--17 to 26 inches; Bt part (60 percent) light yellowish brown (10YR 6/4) silt loam, yellowish brown (10YR 5/4) moist; E part (40 percent) very pale brown (10YR 7/3) silt loam, pale brown (10YR 6/3) moist; few fine faint brown (7.5YR 5/4) moist redox concentrations (due to prolonged saturation from flood irrigation); moderate fine and very fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine and few fine roots; common very fine and few fine dendritic tubular pores; few faint patchy clay films on faces of peds; many silt and sand skeletans on faces of peds; 10 percent gravel; neutral (pH 7.0); clear wavy boundary. (0 to 10 inches thick)
Bt--26 to 41 inches; light yellowish brown (10YR 6/4) clay loam, yellowish brown (10YR 5/4) moist; weak medium prismatic structure parting to moderate medium and fine subangular blocky; slightly hard, friable, moderately sticky and slightly plastic; few very fine roots; common very fine and few fine dendritic tubular pores; common faint patchy clay films on faces of peds; 10 percent gravel; neutral (pH 7.2); clear wavy boundary. (6 to 25 inches thick)
Bk--41 to 60 inches; very pale brown (10YR 7/4) silt loam, yellowish brown (10YR 5/6) moist; moderate medium and fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; very few fine roots; common very fine dendritic tubular pores; 10 percent gravel; disseminated calcium carbonate and many medium and fine patchy soft masses and threads of calcium carbonate; strongly effervescent; slightly alkaline (pH 7.8).
TYPE LOCATION: Beaverhead County, Montana; approximately 1450 feet south and 1400 feet west of the NE corner of sec. 29, T 3 S., R 4 W. Highland Ranch topographic quadrangle, UTM 12T, 0296917e, 5047044n.
RANGE IN CHARACTERISTICS:
Mean annual soil temperature - 35 to 40 degrees F.
Soil moisture control section - between 4 and 12 inches; dry in some or all parts for 90 or more cumulative days in normal years; not dry in all parts for more than half of the cumulative days.
Mollic epipedon thickness - 10 to 18 inches
Depth to argillic horizon - 10 to 24 inches
Redox concentrations can occur in all horizons above the Bt horizon.
Note: Some pedons have an E, E/Bt and or Btk horizon.
A horizons
Value: 4 or 5 dry; 2 or 3 moist
Chroma: 1 to 3; dry or moist
Texture: loam or silt loam
Clay content: 18 to 25 percent
Rock fragments: 0 to 15 percent--0 to 15 percent gravel, 0 to 5 percent cobbles
Reaction: pH 6.0 to 7.5
Bt/E horizon
Hue: 10YR or 2.5Y; dry or moist
Value:
Bt part - 5 or 6 dry; 4 or 5 moist
E part - 7 or 8 dry; 5 or 6 moist
Chroma:
Bt part - 3 or 4; dry or moist
E part - 1 to 3; dry or mosit
Texture: loam or silt loam
Clay content: 18 to 25 percent
Rock fragments: 0 to 35 percent--0 to 35 percent gravel, 0 to 5 percent cobbles
Reaction: pH 6.6 to 7.5
Bt horizon
Hue: 10YR or 2.5Y; dry or moist
Value: 5 or 6 dry; 3 to 5 moist
Chroma: 2 to 4; dry or moist
Texture: loam, clay loam or silt loam
Clay content: 25 to 35 percent
Rock fragments: 0 to 25 percent--0 to 25 percent gravel, 0 to 5 percent cobbles
Reaction: pH 6.0 to 7.5
Bk horizon
Hue: 10YR or 2.5Y; dry or moist
Value: 7 or 8 dry; 5 to 7 moist
Chroma: 2 to 6; dry or moist
Texture: sandy loam, loam or silt loam
Clay content: 15 to 27 percent
Rock fragments: 10 to 40 percent--10 to 40 percent gravel, 0 to 5 percent cobbles
Calcium carbonate equivalent: 5 to 15 percent
Reaction: pH 7.6 to 8.6
COMPETING SERIES:
Plimpton (MT) - do not have secondary carbonate accumulation
Wallrock (WY) - have a seasonally high water table within 60 inches
GEOGRAPHIC SETTING:
Landform - fan remnants, stream terraces and outwash plains
Elevation - 5,900 to 7,100 feet
Slope - 0 to 4 percent
Parent material - mixed alluvium
Climate - long, cold winters; cool, moist springs; short, cool summers
Mean annual precipitation - 14 to 21 inches
Mean annual air temperature - 34 to 39 degrees F.
Frost-free period - 30 to 70 days
GEOGRAPHICALLY ASSOCIATED SOILS: None listed.
DRAINAGE AND PERMEABILITY: Well drained, moderately slow permeability.
USE AND VEGETATION: Bighole 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: Bighole soils are not extensive in the intermountain valleys of southwestern Montana. 44B.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana.
SERIES ESTABLISHED: Beaverhead County, Montana, Big Hole Area, 2005.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - from 2 to 17 inches (A1 and A2 horizons)
Glossic horizon - from 17 to 26 inches (Bt/E horizon)
Argillic horizon - from 17 to 41 inches (Bt/E and Bt horizons)
Horizon with redox concentrations - from 17 to 26 inches (Bt/E horizon)
Horizon of calcium carbonate accumulation - from 41 to 60 inches (Bk horizon)
Particle-size control section - from 17 to 37 inches (Bt/E and part of Bt horizons)
Bighole soils have a cryic temperature regime and an ustic moisture regime and an oxyaquic moisture subclass.
National Cooperative Soil Survey
U.S.A.