LOCATION DUNCOM WY+MTEstablished Series
TAXONOMIC CLASS: Loamy, mixed, superactive Lithic Calcicryolls
TYPICAL PEDON: Duncom gravelly silt loam, rangeland. (Colors are for dry soil unless otherwise noted.)
A--0 to 8 inches; dark gray (10YR 4/1) gravelly silt loam, black (10YR 2/1) moist; moderate fine crumb and granular structure; soft, very friable; 20 percent limestone gravel and flat fragments; calcareous; moderately alkaline (pH 8.0); clear smooth boundary. (6 to 16 inches thick)
Ck--8 to 14 inches; light yellowish brown (2.5Y 6/3) gravelly silt loam, light olive brown (2.5Y 5/3) moist; massive; slightly hard, very friable; 20 percent limestone gravel and flat fragments; calcareous with some visible secondary calcium carbonate occurring as concretions or in thin seams and streaks and as coatings on the limestone fragments. (4 to 14 inches thick)
R--14 inches; hard limestone; weakly fractured but containing less than 5 percent fine material.
TYPE LOCATION: Sheridan County, Wyoming; approximately 1,344 feet north and 752 feet west of S1/4 corner sec. 2, T.55N., R.89W.
RANGE IN CHARACTERISTICS: The mollic epipedon ranges from 6 to 16 inches thick and depth to bedrock ranges from 10 to 20 inches. Typically, these soils are calcareous from the surface downward but they are leached to depths of 2 or 3 inches in some pedons. Organic carbon in the mollic epipedon ranges from 1 to 2 percent and decreases uniformly with increasing depth. The bulk calcium carbonate equivalent of the whole soil ranges from 10 to 40 percent due to the content of limestone fragments and gravel smaller than 2 millimeters. The control section is gravelly silt loam or loam and has 18 to 35 percent clay, 20 to 60 percent silt, and 15 to 50 percent sand. Rock fragments range from 10 to 35 percent with 0 to 10 percent cobbles or flagstones and 5 to 35 percent gravel or channers.
The A horizon has hue of 2.5Y or 10YR, value of 3 through 5 dry, 2 or 3 moist, and chroma of 1 through 3. Typically, it has granular or crumb structure, but it has weak subangular blocky structure in some pedons. This horizon is soft to slightly hard. It is slightly to moderately alkaline (pH 7.8 to 8.4), but is typically more alkaline than pH 8.0.
The Ck horizon has hue of 2.5Y or 10YR. It is moderately or strongly alkaline (pH 8.0 to 8.6) and contains visible accumulations of secondary calcium carbonate.
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING: The Duncom soils are on mountainsides and crests. Slopes range from 2 to 65 percent. The soils formed in material weathered from underlying limestone. At the type location the average annual precipitation is approximately 24 inches, about 12 inches of which falls during the months of April through August.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Chubbs and Nathrop soils and the competing Trump soils. Chubbs and Nathrop soils have argillic horizons and have a depth of 20 to 40 inches to a lithic contact.
DRAINAGE AND PERMEABILITY: Well drained; medium to rapid runoff; moderate permeability.
USE AND VEGETATION: Used principally as native pastureland. Principal native vegetation is sagebrush, Idaho fescue, Columbia needlegrass, king fescue, and yarrow.
DISTRIBUTION AND EXTENT: The high mountainous areas of Wyoming, Colorado, Montana, and Idaho. The series is of large extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Sheridan County, Wyoming, 1932.
REMARKS: Diagnostic horizons and features recognized in this pedon are: a mollic epipedon from the surface to 8 inches (A horizon); a calcic horizon from 8 to 14 inches (Ck horizon); a lithic contact at 14 inches (R horizon).