LOCATION BIGCOULEE               MT

Tentative Series
IRD. KTS-EMM
03/2014

BIGCOULEE SERIES

The Bigcoulee series consists of very deep, moderately well drained soils that formed in colluvium from mixed igneous rock sources. These soils occur on linear and concave mountain slopes. Slopes are 15 to 50 percent. Mean annual precipitation is about 700 mm, and the mean annual temperature is about 3 degrees C.

TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive Pachic Argicryolls

TYPICAL PEDON: Bigcoulee gravelly loam, in Aspen grove on a 33 percent north facing slope at an elevation of 1494 meters (Colors are for dry soil unless otherwise noted).

Oe--0 to 2 cm; moderately decomposed forest litter; clear smooth boundary. (0 to 4 cm thick)

A1--2 to 16 cm; very dark grayish brown (10YR 3/2) gravelly loam, very dark brown (10YR 2/2) moist; moderate medium granular structure; slightly hard, very friable, slightly sticky and slightly plastic; many very fine, fine, medium, and coarse roots; few very fine and fine irregular pores; 15 percent gravel and 5 percent cobbles; slightly acid (pH 6.4); clear wavy boundary.

A2--16 to 38 cm; dark grayish brown (10YR 4/2) gravelly loam, very dark grayish brown (10YR 3/2) moist; moderate medium subangular blocky structure; hard, friable, moderately sticky and moderately plastic; many very fine, fine, medium, and coarse roots; few very fine and fine irregular pores; 20 percent gravel and 5 percent cobbles; slightly acid (pH 6.2); clear wavy boundary. (combined thickness of A horizons - 20 to 50 cm)

Bt1--38 to 64 cm; dark grayish brown (10YR 4/2) very gravelly clay loam, very dark grayish brown (10YR 3/2) moist; moderate medium subangular blocky structure; hard, friable, moderately sticky and moderately plastic; many very fine, fine, medium, and coarse roots; few very fine and fine tubular pores; common (40 percent) distinct clay films on faces of peds; 32 percent gravel and 18 percent cobbles; moderately acid (pH 5.8); gradual wavy boundary.

Bt2--64 to 104 cm; brown (10YR 5/3) very gravelly sandy clay loam, brown (10YR 4/3) moist; strong coarse subangular blocky structure; hard, firm, moderately sticky and moderately plastic; few very fine, fine, medium, and coarse roots; few very fine and fine tubular pores; common (30 percent) distinct clay films on faces of peds; few (1 percent); 40 percent gravel and 15 percent cobbles; moderately acid (pH 5.8); gradual wavy boundary.

Bt3--104 to 150 cm; brown (10YR 5/3) very gravelly sandy clay loam, brown (10YR 4/3) moist; strong coarse subangular blocky structure; hard, firm, moderately sticky and moderately plastic; few very fine, fine, medium, and coarse roots; few very fine and fine tubular pores; common (30 percent) distinct clay films on faces of peds; few (1 percent) fine faint 10YR 5/6 redox concentrations in lower part of horizon; 40 percent gravel and 15 percent cobbles; moderately acid (pH 5.8); (combined thickness of Bt horizons - 100 to 130 cm)

TYPE LOCATION: Chouteau County, Montana; located 605 meters west and 36 meters south of the northeast corner of sec. 32, T.20N., R9E.; Arrow Peak topographic quadrangle; UTM 12T, 0529767e., 5256290n. NAD 83.

RANGE IN CHARACTERISTICS:
Mean annual soil temperature - 1 to 4 degrees C.
Thickness of mollic epipedon - 40 to 75 cm
Depth to seasonal high water table - 100 to 150 cm
Depth to redox concentrations - 100 to 150 cm

A horizons
Value: 2 or 3, moist; 3 or 4 dry
Chroma: 1 or 2; dry or moist
Clay content: 18 to 26 percent
Rock fragments: 5 to 30 percent--5 to 30 percent gravel, 0 to 10 percent cobbles
Reaction: pH 5.6 to 6.5

Bt horizons
Hue: 10YR or 2.5Y
Value: 3, 4 or 5 dry; 2, 3 or 4 moist
Chroma: 2 or 3 dry or moist
Texture: clay loam or sandy clay loam
Clay content: 25 to 35 percent
Rock fragments: 35 to 65 percent--15 to 45 percent gravel, 5 to 25 percent cobbles, 0 to 20 percent stones
Reaction: pH 5.6 to 6.5

COMPETING SERIES:
Angelwhine (CA) - particle size control section is 18 to 25 percent clay.
Aspetill (CA) - particle size control section is 18 to 25 percent clay.
Badwater (WY) - has an ustic soil moisture regime.
Bickmore (UT) - formed from calcareous parent materials.
Blackbear (MT) - is moderately deep to lithic contact.
Bluebell (NV) - has a xeric soil moisture regime.
Booneville (ID) - redox concentrations absent in soil profile.
Buena Vista (CO) - is moderately deep to lithic contact.
Dab (NV) - has a xeric soil moisture regime.
Dailybasin (MT) - has an ustic soil moisture regime.
Delhew (NV) - particle size control section is 14 to 18 percent clay.
Hawkinspeak (CA) - is moderately deep to lithic contact.
Keman (ID) - has a xeric soil moisture regime.
Littlemud (NV) - is moderately deep to lithic contact.
Lostcannon (CA) - particle size control section is 10 to 18 percent clay.
Monibasin (CA) - has a xeric soil moisture regime.
Parkalley (ID) - has a xeric soil moisture regime.
Parkay (UT) - has a xeric soil moisture regime.
Rangertaft (NV) - is moderately deep to lithic contact.
Redbird (SD) - formed from calcareous parent materials.
Rutherford (ID) - is moderately deep to lithic contact.
Sweetmount (CA) - has a xeric soil moisture regime.
Woodhurst (MT) - is moderately deep to lithic contact.

GEOGRAPHIC SETTING:
Landform - mountain slopes.
Elevation - 1370 to 1830 meters.
Slope - 15 to 50 percent.
Parent material - colluvium from mixed igneous rock sources.
Climate - long, cold winters; moist springs; short warm summers.
Mean annual precipitation - 610 to 830 mm.
Mean annual air temperature - 1 to 4 degrees C.
Frost-free period - 40 to 70 days.

GEOGRAPHICALLY ASSOCIATED SOILS: None listed.

DRAINAGE AND PERMEABILITY: moderately well drained, moderate permeability.

USE AND VEGETATION: Bigcoulee soils are used mainly for livestock grazing, wildlife habitat, and recreation. The vegetation is mainly quaking aspen, Douglas-fir, spirea, chokecherry, wild rose, snowberry, current, sweet cicely, western meadowrue, and other miscellaneous shrubs, grasses and forbs.

DISTRIBUTION AND EXTENT: Bigcoulee soils are of small extent in central Montana. MLRA 43B.

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

SERIES PROPOSED: Chouteau County, Montana, 2013. Bigcoulee series is named for a drainage on the Arrow Peak topographic quadrangle.

REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - from 2 to 64 cm (A1, A2, and Bt1 horizons)
Particle-size control section - from 38 to 88 cm (Bt1 and part of Bt2 horizon)

Bigcoulee soils have a cryic temperature regime and a udic moisture regime.

Taxonomic version: Eleventh Edition, 2010.

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National Cooperative Soil Survey
U.S.A.