LOCATION BRISTON MTEstablished Series
TAXONOMIC CLASS: Fine-loamy, mixed, superactive Ustollic Haplocryalfs
TYPICAL PEDON: Briston loam, in rangeland (colors are for dry soil unless otherwise noted).
A--0 to 4 inches; dark grayish brown (10YR 4/2) loam, very dark brown (10YR 2/2) moist; moderate medium subangular blocky structure parting to moderate medium and fine granular; soft, very friable, slightly sticky and non-plastic; many very fine and fine and common medium roots; many fine and very fine interstitial pores; moderately acid (pH 6.0); gradual wavy boundary. (3 to 6 inches thick)
BA--4 to 9 inches; brown (10YR 5/3) loam, very dark grayish brown (10YR 3/2) moist; moderate medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine and fine and common medium roots; many very fine and fine tubular pores; 10 percent gravel; slightly acid (pH 6.2); gradual wavy boundary. (0 to 6 inches thick)
Bt1--9 to 20 inches; brown (7.5YR 5/4) gravelly clay loam, brown (7.5YR 4/4) moist; strong coarse and medium subangular blocky structure; very hard, firm, moderately sticky and moderately plastic; many distinct patchy clay films on faces of peds; common very fine and fine and few medium roots; many very fine tubular pores; 15 percent gravel; slightly acid (pH 6.2); gradual wavy boundary.
Bt2--20 to 29 inches; strong brown (7.5YR 5/6) gravelly clay loam, brown (7.5YR 4/4) moist; strong coarse angular blocky structure; very hard, firm, moderately sticky and moderately plastic; many prominent continuous clay films on faces of peds; few very fine, fine and medium roots; many very fine tubular pores; 30 percent gravel; slightly acid (pH 6.2); gradual wavy boundary.
Bt3--29 to 39 inches; strong brown (7.5YR 5/6) extremely gravelly sandy clay loam, strong brown (7.5YR 4/6) moist; strong medium angular blocky structure; very hard, firm, moderately sticky and moderately plastic; common distinct patchy clay films on faces of peds; few very fine and fine roots; few medium tubular pores; 5 percent cobbles and 60 percent gravel; slightly acid (pH 6.4); gradual wavy boundary. (Combined thickness of Bt horizons 20 to 40 inches)
C--39 to 60 inches; reddish yellow (7.5YR 7/6) extremely gravelly loamy sand, reddish yellow (7.5YR 6/6) moist; single grain; loose, non-sticky and non-plastic; few very fine roots; 10 percent cobbles and 60 percent gravel; slightly acid (pH 6.4).
TYPE LOCATION: Beaverhead County, Montana; approximately 400 feet north and 1400 feet west of the SE corner of sec.15 , T 2 S, R 16 W; USGS Gibbons School, Montana topographic quadrangle; North American Datum 83, zone 12T, UTM 0300516 meters E. 5058864 meters N.
RANGE IN CHARACTERISTICS:
Mean annual soil temperature - 35 to 40 degrees F., Cryic temperature regime.
Mean summer soil temperature - 53 to 57 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. Ustic moisture regime.
Depth to Bt horizon 4 to 9 inches.
Depth to C horizon greater than 30 inches.
Some pedons have a BC horizon above the C.
A horizon Hue: 10YR or 7.5YR
Value: 4 or 5 dry; 2 or 3 moist
Chroma: 2 or 3
Clay content: 15 to 25 percent
Rock fragments: 0 to 15 percent gravel
Reaction: pH 6.0 to 7.2
BA horizon - Hue: 10YR or 7.5YR
Value: 4 or 5 dry; 3 or 4 moist
Chroma: 2, 3 or 4
Texture: loam or fine sandy loam
Clay content: 15 to 25 percent
Rock fragments: 0 to 15 percent gravel
Reaction: pH 6.0 to 7.2
Bt1 horizon - Hue: 10YR or 7.5YR
Value: 4 or 5 dry; 3 or 4 moist
Chroma: 3 or 4
Texture: loam, clay loam or sandy clay loam
Clay content: 20 to 35 percent
Rock fragments: 0 to 35 percent gravel
Reaction: pH 6.0 to 7.2
Bt2 horizon - Hue: 10YR or 7.5YR
Value: 4 or 5 dry; 3 or 4 moist
Chroma: 4 or 6
Texture: loam, clay loam or sandy clay loam
Clay content: 20 to 35 percent
Rock fragments: 0 to 35 percent gravel
Reaction: pH 6.0 to 7.2
Bt3 horizon - Hue: 10YR or 7.5YR
Value: 4 or 5 dry; 3 or 4 moist
Chroma: 4 or 6
Texture: loam, clay loam or sandy clay loam
Clay content: 20 to 35 percent
Rock fragments: 25 to 75 percent; 0 to 10 percent cobbles, 25 to 65 percent gravel
Reaction: pH 6.0 to 7.2
C horizon - Hue: 10YR or 7.5YR
Value: 5, 6 or 7 dry; 4, 5 or 6 moist
Chroma: 4 or 6
Texture: sand, loamy sand or sandy loam
Clay content: 0 to 15 percent
Rock fragments: 35 to 75 percent --0 to 10 percent cobbles, 35 to 65 percent gravel
Reaction: pH 6.0 to 7.2
COMPETING SERIES:
Amesmont - moderately deep to a paralithic contact.
Dunlatop - has a lithologic discontinuity affected by volcanic ash; receives 25 to 32 inches of precipitation.
Gebson - has horizons of carbonate accumulation.
Lymaning (T) - moderately deep to a paralithic contact; has horizons of carbonate accumulation.
Ula - moderately deep to a paralithic contact.
GEOGRAPHIC SETTING:
Landform - remnant outwash terraces and alluvial fans.
Elevation - 6,000 to 6,500 feet.
Slope - 0 to 2 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 50 days
GEOGRAPHICALLY ASSOCIATED SOILS:
This is the Mussigbrod series. Mussigbrod soils have a thick mollic epipedon and are on similar landform positions on mima mounds.
DRAINAGE AND PERMEABILITY: Well drained, moderate permeability.
USE AND VEGETATION: Briston soils are used for rangeland grazing and as wildlife habitat. The vegetation is mainly Idaho fescue, bluebunch wheatgrass, mountain big sagebrush, and other miscellaneous grasses and forbs.
DISTRIBUTION AND EXTENT: Briston soils are not extensive in the intermountain valleys of southwestern Montana. MLRA 44.
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: an ochric epipedon from 0 to 9 inches (A and BA horizons); an argillic horizon 9 to 39 inches (Bt1, Bt2 and Bt3 horizons); a particle-size control section from 9 to 29 inches Bt1 and Bt2 horizons. Briston soils have a cryic temperature regime and an ustic moisture regime.
ADDITIONAL DATA: NSSL data S03MT-001-007