LOCATION SILHOUETTE WYEstablished Series
TAXONOMIC CLASS: Fine, smectitic, mesic Ustic Haplocambids
TYPICAL PEDON: Silhouette clay loam on rangeland. (Colors are for dry soil unless otherwise stated)
A--0 to 2 inches; light brownish gray (10YR 6/2) clay loam, brown (10YR 5/3) moist; weak medium and fine granular structure; slightly hard, very friable, slightly sticky and slightly plastic; slightly effervescent, calcium carbonate disseminated; slightly alkaline (pH 7.8); abrupt smooth boundary. (1 to 4 inches thick)
BA--2 to 6 inches; pale brown (10YR 6/3) clay, brown (10YR 5/3) moist; weak medium subangular blocky structure; hard, friable, moderately sticky and moderately plastic; slightly effervescent; calcium carbonate disseminated; moderately alkaline (pH 8.2); clear smooth boundary. (0 to 6 inches thick)
Bw1--6 to 14 inches; pale brown (10YR 6/3) clay, grayish brown (10YR 5/2) moist; weak fine angular blocky structure; very hard, firm, slightly sticky and slightly plastic; slightly effervescent; calcium carbonate disseminated; moderately alkaline (pH 8.2); gradual smooth boundary.
Bw2--14 to 22 inches; pale brown (10YR 6/3) clay, grayish brown (10YR 5/2) moist; weak fine angular blocky structure; very hard, firm, slightly sticky and slightly plastic; slightly effervescent; calcium carbonate disseminated and as few fine masses; moderately alkaline (pH 8.2); gradual smooth boundary. (Combined Bw horizons 10 to 20 inches thick)
Bk1--22 to 34 inches; very pale brown (10YR 7/3) clay, light brownish gray (10YR 6/2) moist; massive; very hard, firm, slightly sticky and slightly plastic; slightly effervescent; calcium carbonate occurs as common distinct seams and filaments, moderately alkaline (pH 8.0); gradual smooth boundary. (10 to 25 inches thick)
Bk2--34 to 60 inches; light gray (10YR 7/2) clay loam, light brownish gray (10YR 6/2) moist; massive; very hard, very firm, slightly sticky and slightly plastic; slightly effervescent; calcium carbonate occurs as common distinct soft masses; slightly alkaline (pH 7.8).
TYPE LOCATION: Converse County, Wyoming; 150 feet west and 600 feet south of the northeast corner of sec. 20, T. 39 N., R. 72 W. Coal Draw South Quadrangle. 43 degrees 20 minutes 36 seconds north latitude and 105 degrees 31 minutes 17 seconds west longitude.
RANGE IN CHARACTERISTICS: Rock fragments typically are less than 10 percent and are concentrated on the soil surface. These soils typically are calcareous throughout but may be leached in the upper 4 inches in some pedons. Depth to secondary calcium carbonate accumulation ranges from 12 to 24 inches. Depth to paralithic contact, usually shale, is greater than 60 inches. Textures are clay, silty clay, silty clay loam or clay loam throughout. The particle-size control section has 35 to 50 percent clay. The soil is dry in the moisture control section more than half the time cumulative that the soil temperature at a depth of 20 inches is 41 degrees F. which occurs about April 21 to 27, and is dry in all parts of the moisture control section for at least 60 consecutive days from July 15 to October 25 and for at least 90 cumulative days during this period. The mean annual soil temperature is 47 to 51 degrees F., and the soil temperature at a depth of 20 inches is 41 degrees F. or more for 175 to 192 days. Exchangeable sodium content is less than 15 percent. Authigenic gypsum is present in some pedons. EC is 0 to 4 mmhos throughout.
The A horizon has hue of 10YR or 2.5Y, value of 5 to 7 dry, 4 to 6 moist, and chroma of 2 to 4. Reaction is neutral to moderately alkaline.
The Bw horizon has hue of 10YR or 2.5Y, value or 5 or 6 dry, 4 or 5 moist, and chroma of 2 to 4. Reaction is slightly alkaline to strongly alkaline. few faint clay films are present in some pedons, but clay increase is negligible.
The Bk horizon (and C horizons if present) have hue of 10YR to 5Y, value of 5 to 7 dry, 4 to 6 moist, and chroma of 2 to 4. Reaction is slightly alkaline to strongly alkaline. The calcium carbonate equivalent of this horizon ranges from 3 to 14 percent and commonly increases with depth.
COMPETING SERIES: These are the Degator and Savageton series. Degator soils have a frost-free period of less than 105 days. Savageton soils are moderately deep and have paralithic contacts between 20 and 40 inches.
GEOGRAPHIC SETTING: Silhouette soils are on hills, ridges, alluvial fan, fan remnants, relict terraces and fan aprons. Slopes are 0 to 15 percent. The soils formed in fine textured local alluvium derived from calcareous shale. Elevations are 3,500 to 6,500 feet. Precipitation ranges from 10 to 14 inches with over half falling in April, May, and early June and less than one inch falling in each month of July, August, September, and October. The mean annual air temperature ranges from 44 to 49 degrees F. The frost-free season is about 105 to 130 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Savageton soils and the Bahl, Heldt, Samday, Ulm and Zigweid soils. Bahl soils lack cambic horizons. Heldt soils have distinct cracking characteristics. Samday soils have paralithic contacts between 20 and 40 inches. Ulm soils have argillic horizons. Zigweid soils have fine-loamy control sections.
DRAINAGE AND PERMEABILITY: Well drained; medium runoff; slow permeability.
USE AND VEGETATION: These soils are dominantly used for grazing. Potential native vegetation is western wheatgrass, green needlegrass and birdsfoot sagebrush.
DISTRIBUTION AND EXTENT: Powder River Basin and adjacent areas of eastern Wyoming. Series is of limited extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Denver, Colorado
SERIES ESTABLISHED: Converse County, Wyoming, North Part; 1983.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - 0 to 6 inches (A, BA)
Cambic horizon - 6 to 22 inches (Bw1,Bw2)
SIR- WY0451
MLRR- G