LOCATION SWANBOY SDEstablished Series
TAXONOMIC CLASS: Very-fine, smectitic, mesic Aridic Haplusterts
TYPICAL PEDON: Swanboy clay - on a concave slope of 1 percent in native grass. When described the soil was moist below 6 inches. (Colors are for dry soil unless otherwise stated)
A--0 to 1 inch; light olive gray (5Y 6/2) clay, olive (5Y 5/3) moist, with light gray (5Y 7/1) crust about 3 mm thick; moderate fine and medium granular structure; hard, friable, sticky and plastic; cracks about 1 inch wide; slight effervescence; moderately alkaline; abrupt smooth boundary. (1/2 inch to 4 inches thick)
Bss--1 to 6 inches; light gray (5Y 7/2) clay, pale olive (5Y 6/3) moist; weak coarse subangular blocky structure parting to moderate medium and fine angular blocky, extremely hard, very firm, sticky and very plastic; cracks about 1/2 to 1 inch wide; few intersecting slickensides; slight effervescence; strongly alkaline; clear wavy boundary.
Bssz--6 to 12 inches; light gray (5Y 7/2) clay, pale olive (5Y 6/3) moist; weak coarse blocky structure parting to moderate fine blocky; extremely hard, very firm, sticky and very plastic; few intersecting slickensides; common fine accumulations of salt; slight effervescence; strongly alkaline; gradual wavy boundary. (Combined B horizon 8 to 22 inches thick)
C--12 to 60 inches; pale yellow (5Y 7/3) clay, pale olive (5Y 6/3) moist; massive; very hard, firm, sticky and very plastic; few intersecting slickensides; very few fine and medium accumulations of carbonate and gypsum; slight effervescence; strongly alkaline.
TYPE LOCATION: Shannon County, South Dakota; 0.55 mile south and 0.2 mile west of Buffalo Gap road junction; 2,600 feet east and 700 feet north of the southwest corner of sec. 15, T. 40 N., R. 47 W.
RANGE IN CHARACTERISTICS: Swanboy soils commonly contain carbonates throughout, but some pedons do not have carbonates. Visible salts are within 10 inches of the surface, and the surface is dispersed and crusted. When the soil is dry, cracks 1/2 inch to 2 inches wide and several feet long extend to depths below 20 inches. Soil colors are mostly inherited from the parent material.
The A horizon has hue of 10YR, 2.5Y or 5Y, value of 4 to 7 and 3 to 5 moist and chroma of 1 to 3. It is clay or silty clay. It ranges from neutral to strongly alkaline.
The B horizon has hue of 10YR, 2.5Y or 5Y, value of 4 to 7 and 3 to 6 moist and chroma of 2 to 4. It ranges from slightly to strongly alkaline. The horizons has gypsum in some pedons. Some pedons have lower values but are no darker than the C horizon.
The C horizon has hue of 10YR, 2.5Y or 5Y, value of 4 to 7, 3 to 6 moist and chroma of 2 to 4. It ranges from slightly alkaline to strongly alkaline. It has visible salts in some pedons.
COMPETING SERIES: These are the Catman, Kyle, Mcnary, Twotop and Venzuni series. Catman soils are driest during April through June. Kyle and Twotop soils do not have visible salts within depths of 10 inches. Mcnary and Venzuni soils have hues redder than 10YR.
GEOGRAPHIC SETTING: Swanboy soils are nearly level to strongly sloping, have plane to concave surfaces, and are on upland valleys, fans, flats, and stream terraces. Gilai microrelief is in most areas. Slope gradients typically are less than 6 percent but range from 0 to 15 percent. They formed in dense clay alluvium. Mean annual air temperature ranges from 45 to 50 degrees F, and mean annual precipitation ranges from 14 to 24 inches.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Kyle and Twotop soils and the Hisle, Lismas, Orella, Pierre, Samsil, Sansarc, Wasa and Winler soils. The Hisle, Kyle and Twotop soils are on similar positions and the Lismas, Orella, Pierre, Samsil, Sansarc, Wasa and Winler soils are on adjacent higher upland positions. Hisle soils have a natric horizon. Lismas, Orella, Samsil, and Sansarc soils have shale at a depth of less than 20 inches. Pierre, Wasa and Winler soils have shale at a depth of 20 to 40 inches.
DRAINAGE AND PERMEABILITY: Moderately well or well drained. Runoff is medium to very high depending on slope. Permeability is very slow, except after dry periods when initial intake may be rapid due to cracking of surface.
USE AND VEGETATION: Used almost entirely for rangeland. Principal grasses occur as sparse stands of western wheatgrass, montana wheatgrass, and green needlegrass.
DISTRIBUTION AND EXTENT: South Dakota west of the Missouri River, and possible adjacent states to the south and west. The series is extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Denver, Colorado
SERIES ESTABLISHED: Butte County, South Dakota, 1970.
REMARKS: Diagnostic horizons and features recognized in this pedon: Ochric epipedon - the zone from the surface of the soil to a depth of 1 inch ( A horizon); cambic horizon - the zone from 1 to 6 inches (Bss horizon); Vertisol criteria - intersecting slickensides and cracks (Bss, Bssz and C horizon).