LOCATION TWOTOP SD+WYEstablished Series
TAXONOMIC CLASS: Very-fine, smectitic, mesic Aridic Haplusterts
TYPICAL PEDON: Twotop clay - on a southeast-facing slope of 1 percent in native grass. When described the soil was moist to 26 inches. (Colors are for dry soil unless otherwise stated)
A--0 to 3 inches; grayish brown (2.5Y 5/2) clay, dark grayish brown (2.5Y 4/2) moist; vesicular crust in upper 1/2 inch, weak medium and fine subangular blocky structure in lower part; very hard, very firm, sticky and plastic; common roots; slight effervescence; slightly alkaline; clear smooth boundary. (2 to 5 inches thick)
Bw--3 to 9 inches; grayish brown (2.5Y 5/2) clay, dark grayish brown (2.5Y 4/2) moist; weak medium subangular blocky structure; extremely hard, very firm, sticky and plastic; common roots; slight effervescence; slightly alkaline; clear smooth boundary.
Bss--9 to 16 inches; grayish brown (2.5Y 5/2) clay, dark grayish brown (2.5Y 4/2) moist; weak coarse subangular blocky structure; extremely hard, very firm, sticky and plastic; few intersecting slickensides; common roots; few fine accumulations of carbonate; slight effervescence; slightly alkaline; clear smooth boundary. (Combined Bw and Bss horizons 8 to 16 inches thick)
Bssyz--16 to 35 inches; grayish brown (2.5Y 5/2) clay, dark grayish brown (2.5Y 4/2) moist; weak very coarse subangular blocky structure; extremely hard, very firm, sticky and plastic; few interesecting slickensides; few roots; many visible crystals of salt and gypsum; slight effervescence; slightly alkaline; gradual wavy boundary. (10 to 20 inches thick)
C1--35 to 45 inches; grayish brown (2.5Y 5/2) clay, dark grayish brown (2.5Y 4/2) moist; few fine prominent mottles of strong brown (7.5YR 5/8) moist; massive; extremely hard, very firm, sticky and plastic; slight effervescence; slightly alkaline; gradual wavy boundary.
C2--45 to 60 inches; grayish brown (2.5Y 5/2) clay, dark grayish brown (2.5Y 4/2) moist; massive; extremely hard, very firm, sticky and plastic; slightly alkaline.
TYPE LOCATION: Butte County, South Dakota; about 31 miles north and 4 miles east of Belle Fourche, South Dakota; 165 feet east and 1,155 feet south of northwest corner of sec. 4, T. 13 N., R. 3 E.
RANGE IN CHARACTERISTICS: Unweathered shale typically is at depths greater than 5 feet. Typically the soil is calcareous throughout but some pedons are leached to about 10 inches. The soil is neutral or slightly alkaline. Gypsum and other salts typically are between depths of 10 and 20 inches. Clay content of the control section ranges from 60 to 75 percent. When the soil is dry, cracks 1/2 inch to 2 inches more wide and several feet long extend downward through the solum. Rock fragments range from 0 to 5 percent.
The A horizon has hue of 2.5Y or 5Y, value of 4 to 6 and 3 to 5 moist, and chroma of 2 or 3. It is clay, silty clay, clay loam or silty clay loam.
The Bw and Bss horizons have hue of 2.5Y or 5Y, value of 5 or 6 and 4 or 5 moist, and chroma of 2 or 3. They have few accumulation of salts in the lower part of some pedons.
Some pedons have a Bk horizon and has color and texture of the Bw horizon. It typically has accumulation of gypsum and other salts.
The Bssyz horizon has hue of 2.5Y or 5Y, value of 5 or 6 and 4 or 5 moist and chroma of 2 to 4. It has common to many accumulations of gypsum and other salts.
The C horizon has hue of 2.5Y or 5Y, value of 5 or 6 and 4 or 5 moist, and chroma of 2 to 4. It typically is clay but some pedons have strata of silty clay.
COMPETING SERIES: These are the Catman, Kyle, Mcnary, Swanboy and Venzuni series. Catman soils are driest during April through June. Kyle soils have a stronger grade of structure in the surface and do not have salts within depths of 20 inches. Swanboy soils have visible salts within depths of 10 inches. Mcnary and Venzuni soils have hues redder than 2.5Y.
GEOGRAPHIC SETTING: Twotop soils are on nearly level to sloping, plane to concave surfaces on colluvial fans, hills, ridges in upland valleys and. Slope gradients range from 0 to 9 percent. Gilgai microrelief is in most areas. The soil formed in clay alluvium. Mean annual air temperature ranges from 45 to 48 degrees F, and mean annual precipitation ranges from 10 to 17 inches.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Kyle and Swanboy soils and the Hisle, Lismas, Pierre, Wasa and Winler soils. Kyle and Swanboy soils are on similar landscapes. Hisle soils are in similar landscape and have a natric horizon. Lismas soils are on nearby steep landscapes and have shale within 20 inches of the surface. Pierre, Wasa, and Winler soils are on steeper landscapes above the Twotop soils. They have bedded shale within depths of 40 inches. In addition, Wasa soils have salts within 8 inches of the surface.
DRAINAGE AND PERMEABILITY: Well drained. Runoff is medium to very high on sloping areas and low on nearly level areas. Permeability is very slow.
USE AND VEGETATION: Rangeland. Native vegetation is mainly western wheatgrass and montana wheatgrass. Green needlegrass is in some areas.
DISTRIBUTION AND EXTENT: Western South Dakota and eastern Wyoming. The series is of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Denver, Colorado
SERIES ESTABLISHED: Butte County, South Dakota, 1970.
REMARKS: Diagnostic and other features of this pedon are:
Vertic feature - intersecting slickensides and some gilgai microrelief.
Surface condition - granular surface mulch - surface is not covered with an understory of short vegetation but is exposed due to a nearly pure stand of wheatgrass.
Moisture regime - aridic-ustic
The classification has been changed from Typic Torrerts to Aridic Haplusterts based on precipitation.