LOCATION BIG HORN WY+MTEstablished Series
TAXONOMIC CLASS: Fine, smectitic, mesic Ustic Paleargids
TYPICAL PEDON: Big Horn loam-rangeland. (Colors are for air dry soil unless otherwise stated.)
A--0 to 4 inches; grayish brown (10YR 5/2) loam,very dark grayish brown (10YR 3/2) moist, dark grayish brown (10YR 4/2) rubbed; soft, very friable; moderate fine granular structure; noncalcareous; neutral (pH 7.2); abrupt smooth boundary. (3 to 6 inches thick)
Bt1--4 to 9 inches; grayish brown (10YR 5/2) clay, very dark grayish brown (10YR 3/2) moist, dark grayish brown (10YR 4/2) rubbed; extremely hard, friable, very plastic; strong medium prismatic structure parting to strong fine angular blocky; common thin clay films on faces of peds and in root channels and pores; weak and inconsistent gray coatings on faces of peds in the upper inch; slightly alkaline (pH 7.4); gradual smooth boundary. (3 to 10 inches thick)
Bt2--9 to 22 inches; grayish brown (10YR 5/2) clay, dark grayish brown (10YR 4/2) moist; extremely hard, friable, very plastic; strong medium prismatic structure parting to strong medium angular blocky; thick continuous clay films on faces of peds and in root channels and pores; 5 percent pebbles; slightly alkaline (pH 7.6); gradual smooth boundary. (6 to 18 inches thick)
Btk--22 to 26 inches; light brownish gray (2.5Y 6/2) clay loam, dark grayish brown (2.5Y 4/2) moist; moderate coarse prismatic structure parting to moderate coarse angular and subangular blocky; extremely hard, firm, plastic; common thin clay films on faces of peds and in root channels; strongly effervescent, calcium carbonate as nodules and in thin seams and streaks; (10 percent pebbles) moderately alkaline (pH 8.2). (3 to 6 inches thick)
Bk1--26 to 40 inches; light gray (2.5Y 7/2) gravelly clay loam, light brownish gray (2.5Y 6/2) moist; very weak coarse subangular blocky structure; very hard, firm, plastic; violently effervescent, calcium carbonate as concretions, in thin seams and streaks and in carbonate equivalent 20 percent; 25 percent pebbles, moderately alkaline (pH 8.2); gradual smooth boundary. (6 to 20 inches thick)
Bk2--40 to 60 inches; grayish brown (2.5Y 5/2) gravelly clay loam, dark grayish brown (2.5Y 4/2) moist; massive; hard, friable; strongly effervescent, common visible secondary calcium carbonate in this horizon but less than in the horizon above; 25 percent pebbles; moderately alkaline (pH 8.2).
TYPE LOCATION: Johnson County, Wyoming; NW1/4 NW1/4 sec. 9, T.45N., R.82W.
RANGE IN CHARACTERISTICS: Depth to calcareous material ranges from 12 to 30 inches. Organic carbon in the upper 15 inches averages .6 to 1.2 percent and the sand/clay ratio ranges from less than 1 to 2. These soils have an abrupt textural boundary between the A and Bt horizons and have a thin discontinuous E horizon immediately above the Bt horizon in some pedons. Coarse fragments range from 0 to 12 percent and cobbles are 0 to 3 percent in most of the solum and increase with increasing depth. Mean annual soil temperature ranges from 47 degrees to 53 degrees F.
The A horizon has hue of 2.5Y or 10YR, value of 5 or 6 dry, 3 or 4 moist, and chroma of 2 or 3. When the value of the A horizon is as dark as 5 dry and 3 moist the horizon is thin enough so that if the soil is mixed to 7 inches, it has an ochric epipedon. It is neutral or slightly alkaline.
The Bt horizon has hue of 2.5Y through 7.5YR, value of 5 or 6 dry, 3 through 5 moist, and chroma of 2 or 3. It is typically clay but ranges in clay from 35 to 50 percent with more than 15 percent fine sand or coarser. It is neutral or slightly alkaline.
The Btk when present has the combined properties of the Bt and Bk horizons.
The Bk horizon has hue of 2.5Y or 10YR value of 5 through 7 dry, 4 through 6 moist and chroma of 2 through 4. This horizon has 15 to 30 percent calcium carbonate equivalent and is moderately alkaline or strongly alkaline.
COMPETING SERIES: These are the Adena, Bidman, Briggsdale, Campo, Demar, Gibbler, and Mughut series. Adena soils have solums thinner than 15 inches. Bidman and Campo soils lack a calcic horizon. Briggsdale, Gibbler, and Mughut soils have bedrock at depths of less than 40 inches. Demar soils are acid.
GEOGRAPHIC SETTING: The Big Horn soils are on old alluvial fans and high terraces. Elevation is 3,500 to 5,500 feet. Slope gradients range from 0 to 15 percent. These soils formed in alluvial fan sediments of comparatively old age. At the Rev. PSD 880414 type location the average annual precipitation is 12 to 19 inches and approximately 8 to 9 inches of this falls during the months of April through August. The mean annual temperature is 48 degrees F. and the mean summer temperature is 68 degrees F. The frost-free season is 95 to 125 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Briggsdale soils and the Wyarno soils. Wyarno soils have a gradual A1 to B2t horizon boundary.
DRAINAGE AND PERMEABILITY: Well drained; medium to rapid runoff; moderately slow permeability.
USE AND VEGETATION: Used mainly as native pastureland; however, they may be tilled in some locations. Principal native vegetation is blue grama, and other grasses.
DISTRIBUTION AND EXTENT: Eastern Wyoming, Colorado, and possibly Montana. The series is of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Sheridan County, Wyoming, 1932.