LOCATION BROBACK WY
Tentative Series
Rev. DMM-RJS
02/2014
BROBACK SERIES
The Broback series consists of very deep, well drained soils that formed in slope alluvium derived from metamorphic and sedimentary rock over residuum from sandstone and shale. These soils are on eroded fan remnants sideslopes and escarpments. Slopes are 4 to 35 percent. Mean annual precipitation is 330 mm, and mean annual air temperature is about 2.0 degrees C.
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, frigid Aridic Haplustalfs
TYPICAL PEDON: Broback very gravelly sandy loam, in rangeland (colors are for dry soil unless otherwise noted).
A--0 to 5 cm; brown (10YR 4/3), very gravelly sandy loam, very dark grayish brown (10YR 3/2), moist; weak fine subangular blocky; soft, very friable, nonsticky and nonplastic; many fine roots; many fine interstitial pores; 40 percent gravel, 10 percent cobbles; slightly alkaline (pH 7.6); clear smooth boundary. (4 to 10 centimeters thick)
Bt--5 to 17 cm; brown (10YR 5/3), very gravelly clay loam, brown (10YR 4/3), moist; moderate medium and coarse subangular blocky structure; moderately hard, firm, moderately sticky and moderately plastic; many fine roots; many fine tubular pores; 5 percent distinct clay films on all faces of peds, and 2 percent faint clay bridges between sand grains; 45 percent gravel, 10 percent cobbles; slightly alkaline (pH 7.6); clear smooth boundary. (8 to 20 centimeters thick)
Btk1--17 to 41 cm; yellowish brown (10YR 5/4), extremely gravelly sandy clay loam, dark yellowish brown (10YR 4/4), moist; weak fine and medium subangular blocky structure; moderately hard, firm, moderately sticky and moderately plastic; many fine roots; many fine tubular pores; 5 percent faint clay bridges between sand grains; 55 percent gravel, 10 percent cobbles; 20 percent carbonate coats on rock fragments; very slightly effervescent; slightly alkaline (pH 7.6); gradual wavy boundary. (15 to 30 centimeters thick)
2Btk2--41 to 60 cm; olive gray (5Y 5/2), gravelly sandy clay loam, olive gray (5Y 4/2), moist; moderate coarse and very coarse subangular blocky structure; moderately hard, firm, moderately sticky and moderately plastic; common fine roots; many fine tubular pores; 8 percent distinct clay films on all faces of peds; 20 percent gravel, 10 percent cobbles; 5 percent carbonate masses in matrix, and 25 percent carbonate coats on rock fragments; strongly effervescent; moderately alkaline (pH 8.2); clear smooth boundary. (15 to 30 centimeters thick)
2Btk3--60 to 82 cm; olive gray (5Y 5/2), loam, olive gray (5Y 4/2), moist; moderate coarse and very coarse subangular blocky structure; slightly hard, friable, moderately sticky and moderately plastic; common fine roots; many fine tubular pores; 2 percent distinct clay films on all faces of peds; 5 percent gravel; 10 percent carbonate masses in matrix; strongly effervescent; very strongly alkaline (pH 9.2); clear smooth boundary. (15 to 30 centimeters thick)
2BCk--82 to 200 cm; light olive gray (5Y 6/2), very fine sandy loam, olive gray (5Y 5/2), moist; weak medium subangular blocky structure; soft, very friable, slightly sticky and slightly plastic; common fine roots; many fine tubular pores; 2 percent parachanners; 2 percent carbonate masses in matrix, and finely disseminated calcium carbonate; slightly effervescent; moderately alkaline (pH 8.4).
TYPE LOCATION: Sublette County, Wyoming; USGS Ross Butte, Wyoming topographic quadrangle; 42 degrees 42 minutes 24.00 seconds north latitude and 109 degrees 50 minutes 47.00 seconds west longitude.
RANGE IN CHARACTERISTICS:
Soil Temperature - 3.5 to 6.0 degrees C.
Depth to argillic horizon - 4 to 10 cm
Depth to secondary carbonates - 15 to 30 cm
Depth to lithologic discontinuity - 30 to 50 cm
Note: Particle-size control section rock fragments - averages greater than 35 percent
A horizon
Hue: 7.5YR or 10YR; dry or moist
Value: 3 or 4 dry or moist
Chroma: 2 or 3 dry or moist
Texture: sandy loam
Clay content: 10 to 18 percent
Rock Fragments: 35 to 60 percent--35 to 50 percent gravel, 0 to 15 percent cobbles
Reaction: pH 6.8 to 7.6
Bt horizon
Hue: 7.5YR or 10YR; dry or moist
Value: 4 or 5 dry or moist
Chroma: 3 or 4 dry or moist
Texture: sandy clay loam, clay loam, loam
Clay content: 20 to 30 percent
Rock Fragments: 40 to 70 percent--35 to 65 percent gravel, 0 to 15 percent cobbles
Reaction: pH 6.8 to 7.8
Btk1 horizon
Hue: 7.5YR or 10YR; dry or moist
Value: 4 or 5 dry or moist
Chroma: 3 or 4 dry or moist
Texture: sandy clay loam, clay loam, loam
Clay content: 20 to 30 percent
Rock Fragments: 40 to 70 percent--35 to 65 percent gravel, 0 to 15 percent cobbles
Calcium carbonate equivalent: 1 to 5 percent
Reaction: pH 7.6 to 8.0
2Btk2 horizon
Hue: 2.5Y or 5Y; dry or moist
Value: 5 or 6 dry; 4 or 5 moist
Chroma: 2 or 3; dry or moist
Texture: sandy clay loam, loam, clay loam
Clay content: 20 to 30 percent
Rock Fragments: 0 to 35 percent--0 to 30 percent quartzite gravel; 0 to 15 percent quartzite cobbles
Calcium carbonate equivalent: 5 to 15 percent
Sodium adsorption ratio: 0 to 5
Reaction: pH 7.9 to 8.6
2Btk3 horizon
Hue: 2.5Y or 5Y; dry or moist
Value: 5 or 6 dry; 4 or 5 moist
Chroma: 2 or 3; dry or moist
Texture: sandy clay loam, loam, clay loam
Clay content: 20 to 30 percent
Rock Fragments: 0 to 35 percent--0 to 30 percent quartzite gravel; 0 to 15 percent quartzite cobbles
Calcium carbonate equivalent: 5 to 15 percent
Sodium adsorption ratio: 3 to 12
Reaction: pH 8.2 to 9.2
2BCk horizon
Hue: 2.5Y or 5Y; dry or moist
Value: 5 or 6 dry; 4 or 5 moist
Chroma: 2 or 3; dry or moist
Texture: very fine sandy loam, fine sandy loam, sandy loam
Clay content: 12 to 20 percent
Parafragments: 2 to 15 percent shale parachanners
Calcium carbonate equivalent: 2 to 5 percent
Sodium adsorption ratio: 3 to 12
Reaction: pH 8.2 to 9.2
COMPETING SERIES:
Geohrock (MT) - have part of an argillic horizon that is noncalcareous
GEOGRAPHIC SETTING:
Landform - eroded fan remnant sideslopes, escarpments
Elevation - 2,150 to 2,300 meters
Slope - 4 to 35 percent
Parent Material - slope alluvium derived from metamorphic and sedimentary rock over residuum from sandstone and shale
Climate - long, cold winters; cool, moist springs; short, cool summers
Mean annual precipitation - 275 to 350 mm with peak periods of precipitation occurring during the spring
Mean annual air temperature: - 2.0 to 4.0 degrees C.
Frost-free period - 45 to 65 days
GEOGRAPHICALLY ASSOCIATED SOILS: None listed.
DRAINAGE AND PERMEABILITY: Well drained, moderate permeability.
USE AND VEGETATION: Broback soils are primarily used for rangeland. The potential native vegetation is mainly Wyoming big sagebrush, Hood's phlox, Letterman's needlegrass, mock goldenweed, bottlebrush squirreltail, western wheatgrass and bluebunch wheatgrass.
DISTRIBUTION AND EXTENT: Broback soils are of small extent in southwestern Wyoming. MLRA - 34A.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana.
SERIES PROPOSED: Sublette County, Wyoming, 2014. The series name is a coined.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - 0 to 5 cm (A)
Argillic horizon - 5 to 82 cm (Bt, Btk1, 2Btk2, 2Btk3)
Secondary carbonates - 17 to 200 cm (Btk1, 2Btk2, 2Btk3, 2BCk)
Lithologic discontinuity - 41 to 200 cm (2Btk2, 2Btk3, 2BCk)
Particle-size horizon control section - from 5 to 55 cm (Bt, Btk1, part of 2Btk2)
Broback soils have a frigid temperature regime and an ustic moisture regime that borders on aridic.
National Cooperative Soil Survey
U.S.A.