LOCATION HELMVILLE MT

Established Series
Rev. GAR-JJU-RJS
04/2011

HELMVILLE SERIES

The Helmville series consist of very deep, well drained soils that formed in colluvium and alluvium derived from limestone, argillite, and igneous rocks. These soils are on mountain slopes. Slopes are 2 to 70 percent. Mean annual precipitation is about 25 inches, and mean annual air temperature is about 37 degrees F.

TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive Eutric Haplocryalfs

TYPICAL PEDON: Helmville cobbly loam, forested (colors are for dry soil unless otherwise noted).

Oi--0 to 2 inches; forest litter, slightly decomposed.

E--2 to 10 inches; yellowish brown (10YR 5/4) cobbly loam, dark brown (7.5YR 3/4) moist; weak fine granular structure; soft, friable, nonsticky and nonplastic; many very fine, fine and medium roots; many very fine and fine discontinuous irregular pores; 15 percent gravel, 15 percent cobbles; neutral (pH 6.6); gradual wavy boundary. (5 to 15 inches thick)

Bt1--10 to 14 inches; dark yellowish brown (10YR 4/4) very cobbly clay loam, brown (7.5YR 4/4) moist; weak medium subangular blocky structure parting to weak medium granular; slightly hard, friable, slightly sticky and moderately plastic; many very fine and fine, common medium, and few coarse roots; many very fine and fine discontinuous irregular pores; many thin continuous clay films on faces of peds; 20 percent gravel, 25 percent cobbles; neutral (pH 7.2); gradual wavy boundary. (0 to 8 inches thick)

Bt2--14 to 25 inches; brownish yellow (10YR 6/6) very cobbly clay loam, yellowish brown (10YR 5/6) moist; weak medium subangular blocky structure; slightly hard, friable, moderately sticky and moderately plastic; common very fine, fine and medium roots; many very fine and fine discontinuous irregular pores; many thin continuous clay films on faces of peds; 25 percent gravel, 30 percent cobbles; slightly alkaline (pH 7.6); clear smooth boundary. (9 to 20 inches thick)

Bk--25 to 60 inches; brownish yellow (10YR 6/6) very cobbly clay loam, yellowish brown (10YR 5/6) moist; weak fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; few very fine and fine roots; many very fine and fine discontinuous irregular pores; 30 percent gravel and 30 percent cobbles; finely disseminated calcium carbonate, continuous distinct calcium carbonate coating on gravel and cobbles, and faint and distinct calcium carbonate casts on undersides of the rock fragments; violently effervescent; moderately alkaline (pH 7.9).

TYPE LOCATION: Granite County, Montana; 1,400 feet north and 1,800 feet east of the SW corner of sec. 18, T. 12N., R. 13W.

RANGE IN CHARACTERISTICS:
Soil temperature - 36 to 42 degrees F.
Depth to top of argillic horizon - 5 to 15 inches
Depth to a calcic horizon - 14 to 40 inches
Base saturation - more than 50 percent throughout
Surface stones or boulders - 0 to 20 percent

E horizon
Hue: 10YR or 7.5YR; dry or moist
Value: 5 to 7 dry; 3 to 5 moist
Chroma: 2 to 4; dry or moist
Clay content: 18 to 27 percent
Rock fragments: 15 to 35 percent--5 to 30 percent gravel or channers, 0 to 20 percent cobbles, flagstones and stones
Reaction: pH 5.6 to 7.3

Bt1 horizon
Hue: 10YR or 7.5YR; dry or moist
Value: 4 to 6 dry; 3 to 5 moist
Chroma: 4 to 6; dry or moist
Clay content: 20 to 38
Texture: loam or clay loam
Rock fragments: 30 to 60 percent--15 to 50 percent gravel or channers, 0 to 35 percent cobbles and stones
Reaction: pH 6.1 to 7.8

Bt2 horizon
Hue: 10YR or 7.5YR; dry or moist
Value: 4 to 6 dry; 3 to 5 moist
Chroma: 4 to 6; dry or moist
Clay content: 27 to 35 percent
Rock fragments: 35 to 60 percent--15 to 50 percent gravel or channers, 0 to 35 percent cobbles and stones
Reaction: pH 6.1 to 7.8

Bk horizon
Hue: 10YR or 2.5Y; dry or moist
Value: 5 to 7 dry; 4 or 5 moist
Chroma: 2 to 6; dry or moist
Texture: loam, sandy loam, or clay loam
Clay content: 18 to 30 percent
Rock fragments: 40 to 90 percent--20 to 45 percent gravel or channers, 0 to 45 percent cobbles and stones
Calcium carbonate equivalent: 15 to 40 percent
Reaction: pH 7.4 to 8.4

COMPETING SERIES:
Frisco (CO) - does not have secondary calcium carbonate accumulation
Lonniebee (MT) - is moderately deep to a lithic contact
Needleton (CO) - does not have secondary calcium carbonate accumulation
Tamarron (CO) - is moderately deep to a paralithic contact
Tigeron (MT) - does not have secondary calcium carbonate accumulation
Worock (MT) - does not have secondary calcium carbonate accumulation

GEOGRAPHIC SETTING:
Landform - mountain slopes
Elevation - 4,600 to 8,600 feet
Slope - 2 to 70 percent
Parent material - colluvium and alluvium derived from limestone, argillite, and igneous rocks
Climate - long, cold winters; moist springs; warm summers
Mean annual precipitation - 19 to 40 inches
Mean annual air temperature - 35 to 40 degrees F.
Frost-free period - 30 to 70 days

GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Worock and the Relyea series. Relyea soils are clayey-skeletal. These soils are on similar landform positions.

DRAINAGE AND PERMEABILITY: Well drained; moderately slow permeability.

USE AND VEGETATION: Helmville soils are used for timber production, watershed, and wildlife. The native vegetation is mainly Douglas-fir, lodgepole pine, subalpine fir, pinegrass, heartleaf arnica, white spiraea, western meadowrue, Englemann aster, common snowberry, beargrass, blue huckleberry, and grouse whortleberry.

DISTRIBUTION AND EXTENT: Helmville soils are of moderate extent in western and southwestern Montana. MLRAs - 43A, 43B.

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

SERIES ESTABLISHED: Lewis and Clark County Area, Montana, 1991; proposed in Powell County, Montana, 1986.

REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - from 0 to 10 inches (Oi, E horizons)
Argillic horizon - from 10 to 25 inches (Bt1, Bt2 horizons)
Calcic horizon - from 25 to 60 inches (Bk horizon)
Particle-size control section - from 10 to 25 inches (Bt1, Bt2 horizons)

Helmville soils have a cryic temperature regime and an udic moisture regime.

ADDITIONAL DATA: Soil interpretation records - MT1036, MT1037.

National Cooperative Soil Survey
U.S.A.