LOCATION THUNDERHEAD MT
Established Series
Rev. GFB-JJU-RJS
06/2011
THUNDERHEAD SERIES
The Thunderhead series consists of moderately deep, well drained soils that formed in slope alluvium or colluvium over residuum derived from sedimentary or igneous rock. They are on cuestas, hills, mountain slopes and ridges. Slopes are 8 to 15 percent. The mean annual precipitation is about 12 inches, and the mean annual air temperature is about 43 degrees F.
TAXONOMIC CLASS: Fine-loamy, mixed, superactive, frigid Calcidic Argiustolls
TYPICAL PEDON: Thunderhead gravelly loam, in rangeland (colors are for dry soil unless otherwise noted).
A--0 to 5 inches; light olive brown (2.5Y 5/3) gravelly loam, dark olive brown (2.5Y 3/3) moist; weak fine and medium subangular blocky structure parting to weak fine granular; soft, very friable, slightly sticky and slightly plastic; many very fine and few fine roots; 15 percent gravel; neutral (pH 7.0); clear smooth boundary. (5 to 7 inches thick)
Bt--5 to 13 inches; light olive brown (2.5Y 5/3) clay loam, olive brown (2.5Y 4/3) moist; weak medium prismatic structure parting to weak fine granular; slightly hard, friable, moderately sticky and slightly plastic; many very fine and few fine roots; many distinct clay films on faces of peds and on surface of fragments; 10 percent gravel; neutral (pH 7.3); clear wavy boundary. (4 to 16 inches thick)
Bk1--13 to 22 inches; light gray (2.5Y 7/2) gravelly loam, light yellowish brown (2.5Y 6/3) moist; moderate fine and medium subangular blocky structure; slightly hard, friable, moderately sticky and slightly plastic; common very fine and few fine roots; 20 percent gravel and 5 percent cobbles; violently effervescent; finely disseminated calcium carbonate and common soft masses of calcium carbonate; moderately alkaline (pH 8.1); clear wavy boundary. (5 to 13 inches thick)
Bk2--22 to 28 inches; pale yellow (2.5Y 7/3) very gravelly silty clay loam, light yellowish brown (2.5Y 6/3) moist; moderate fine and medium subangular blocky structure; slightly hard, friable, moderately sticky and slightly plastic; few fine roots; 30 percent gravel and 15 percent cobbles; finely disseminated calcium carbonate and common soft masses of calcium carbonate; violently effervescent; moderately alkaline (pH 8.2); clear smooth boundary. (5 to 10 inches thick)
Cr--28 to 40 inches; light olive gray (5Y 6/2) semiconsolidated sedimentary beds that crush to silt loam, dark gray (5Y 4/1) moist; strongly effervescent; slightly alkaline (pH 7.7); clear smooth boundary. (0 to 13 inches thick)
R--40 inches; hard sedimentary rock.
TYPE LOCATION: Beaverhead County, Montana; 1,300 feet north and 1,200 feet east of the southwest corner of sec. 18, T. 3S, R. 9W; Storm Peak topographic quadrangle; Lat. 45 degrees 34 minutes 21 seconds N. and Long. 112 degrees 46 minutes 15 seconds W.
RANGE IN CHARACTERISTICS:
Mean annual soil temperature - 38 to 44 degrees F.
Thickness of mollic epipedon - 7 to 15 inches
Depth to argillic horizon - 5 to 7 inches
Depth to calcic horizon - 11 to 26 inches
Depth to paralithic contact - 22 to 40 inches
Depth to lithic contact - 25 to 40 inches
A horizon
Hue: 2.5Y, 10YR or 7.5YR; dry or moist
Value: 4 or 5 dry; 2 or 3 moist
Chroma: 2 or 3; dry or moist
Texture: sandy loam or loam
Clay content: 15 to 25 percent
Rock fragments: 0 to 35 percent--0 to 25 percent gravel, 0 to 10 percent cobbles
Reaction: pH 6.6 to 7.6
Bt horizon
Hue: 2.5Y, 10YR or 7.5YR; dry or moist
Value: 5 or 6 dry; 4 or 5 moist
Chroma: 2 to 6; dry or moist
Texture: sandy clay loam, loam or clay loam
Clay content: 22 to 35 percent
Rock fragments: 0 to 35 percent--0 to 25 percent gravel, 0 to 10 percent cobbles
Reaction: pH 6.6 to 7.6
Bk1 horizon
Hue: 2.5Y, 10YR, 7.5YR or 5Y; dry or moist
Value: 6 or 7 dry; 5 or 6 moist
Chroma: 2 or 3; dry or moist
Texture: sandy loam, sandy clay loam, loam or clay loam
Clay content: 15 to 30 percent
Rock fragments: 10 to 35 percent--10 to 25 percent gravel, 0 to 10 percent cobbles
Calcium carbonate equivalent: 5 to 15 percent
Reaction: pH 7.6 to 8.6
Bk2 horizon
Hue: 5Y, 2.5Y, 10YR or 7.5YR; dry or moist
Value: 6 or 7 dry; 5 or 6 moist
Chroma: 2 to 4; dry or moist
Texture: silty clay loam, sandy loam or loam
Clay content: 15 to 30 percent
Rock fragments: 20 to 60 percent--20 to 45 percent gravel, 0 to 15 percent cobbles
Calcium carbonate equivalent: 15 to 30 percent
Reaction: pH 7.6 to 8.6
COMPETING SERIES:
Cortyzack (CO) - are very deep
Eldgin (UT) - are very deep
Emlin (CO) - are very deep
Fortlogan (MT) - are deep to a paralithic contact
Hysoop (MT) - are very deep
Morval (NM) - are very deep
Notter (UT) - are very deep
Nuley (MT) - are deep to a lithic contact
Varney (MT) - are very deep
Villa Grove (CO) - are very deep
GEOGRAPHIC SETTING:
Landform - cuestas, hills, mountain slopes and ridges
Elevation - 5,000 to 6,500 feet
Slope - 8 to 55 percent
Parent material - slope alluvium or colluvium over residuum derived from sedimentary or igneous rock
Climate - long, cold winters; moist springs; warm summers
Mean annual precipitation - 10 to 14 inches
Mean annual temperature - 39 to 45 degrees F.
Frost-free period - 70 to 90 days
GEOGRAPHICALLY ASSOCIATED SOILS: None listed.
DRAINAGE AND PERMEABILITY: Well drained; moderate permeability.
USE AND VEGETATION: Thunderhead soils are used mainly for rangeland. Native vegetation is mainly bluebunch wheatgrass, needleandthread, prairie junegrass, rubber rabbitbrush, fringed sagewort, phlox, and big sage.
DISTRIBUTION AND EXTENT: Thunderhead soils are of small extent in southwestern Montana. MLRAs - 43B, 46.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana.
SERIES ESTABLISHED: Beaverhead County, Montana, 2001.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - from 0 to 7 inches mixed (A, upper part of Bt horizons)
Argillic horizon - from 5 to 13 inches (Bt horizon)
Secondary calcium carbonate accumulation - from 13 to 28 inches (Bk1, Bk2 horizons)
Calcic horizon - from 22 to 28 inches (Bk2 horizon)
Paralithic contact - at 28 inches (Cr horizon)
Lithic contact - at 40 inches (R horizon)
Particle size control section - from 5 to 13 inches (Bt horizon)
Thunderhead soils have a frigid temperature regime and an ustic moisture regime that borders on aridic.
National Cooperative Soil Survey
U.S.A.