LOCATION BULLFLAT SDEstablished Series
TAXONOMIC CLASS: Fine-loamy, mixed, superactive, frigid Typic Argiudolls
TYPICAL PEDON: Bullflat silt loam - on a southeast-facing slope of 1 percent under alfalfa at 4250 feet. When described, the soil was moist to 32 inches and dry below. (Colors are for dry soil unless otherwise noted).
Ap--0 to 6 inches; dark grayish brown (10YR 4/2) silt loam, very dark brown (10YR 2/2) moist; moderate fine granular structure; soft, very friable; 5 percent fragments of rock; neutral; clear smooth boundary. (4 to 12 inches thick)
Bt1--6 to 10 inches; brown (10YR 5/3) clay loam, dark brown (10YR 3/3) moist; weak fine and medium subangular blocky structure parting to moderate medium granular; hard, friable; 5 percent fragments of rock; neutral; clear smooth boundary.
Bt2--10 to 18 inches; brown (7.5YR 5/4) clay loam, dark brown (7.5YR 4/4) moist; weak medium prismatic structure parting to moderate medium and fine subangular blocky; very hard, friable; 5 percent fragments of rock; neutral; clear smooth boundary.
Bt3--18 to 21 inches; yellowish brown (10YR 5/4) clay loam, dark yellowish brown (10YR 4/4) moist; weak medium and coarse prismatic structure parting to weak medium subangular blocky; very hard, friable; 5 percent fragments of rock; friable; neutral; abrupt wavy boundary. (Combined Bt horizons is 6 to 22 inches thick.)
Bk--21 to 28 inches; light yellowish brown (10YR 6/4) clay loam, yellowish brown (10YR 5/4) moist; weak coarse subangular blocky structure; hard, friable; 10 percent fragments of rock; many coarse to fine accumulations of carbonate; strong effervescence; moderately alkaline; clear smooth boundary. ( 0 to 20 inches thick)
2C1--28 to 32 inches; very pale brown (10YR 7/4) gravelly clay loam, light yellowish brown (10YR 6/4) moist; massive; slightly hard, friable; 30 percent fragments of rock; few fine accumulation of carbonate; strong effervescence; moderately alkaline; clear smooth boundary.
2C2--32 to 60 inches; very pale brown (10YR 8/4) very cobbly clay loam, very pale brown (10YR 7/4) moist; massive; slightly hard, friable; carbonates coat undersides of pebbles; 40 percent fragments of rock; strong effervescence; moderately alkaline.
TYPE LOCATION: Pennington County, South Dakota; about 9 miles south and 2 miles west of Rapid City; 2500 feet north and 800 feet east of the southwest corner of sec. 21, T. 1 S., R. 7 E. .
RANGE IN CHARACTERISTICS: Depth to carbonates typically is 12 to 22 inches, but ranges from 10 to 34 inches. Rock fragments which are dominantly pebbles, cobbles, and channers range from 0 to 10 percent by volume in the A and Bt horizons and 15 to 50 percent by volume in the C horizon. Depth to consolidated bedrock typically is greater than 60 inches, but ranges from 40 to 60 inches in some pedons. Some pedons have common to many fine particles of mica.
The A horizon has hue of 5YR, 7.5YR, or 10YR; value of 3 or 4 and 2 or 3 moist; and chroma of 1 or 2. It is silt loam or loam. It ranges from medium acid to neutral.
The Bt horizon has hue of 5YR, 7.5YR, or 10YR; value of 4 to 6 and 3 or 4 moist; and chroma of 3 or 4. It is clay loam, silty clay loam, or silt loam. It is slightly acid or neutral.
The Bk horizon has hue of 5YR, 7.5YR, or 10YR; value of 5 to 7 and 4 to 6 moist; and chroma of 3 or 4. It is clay loam, silty clay loam or silt loam and contains up to 35 percent by volume of fragments of rock. It typically has disseminated carbonates or common to many accumulations of carbonate. It is slightly alkaline or moderately alkaline.
Some pedons have a C horizon.
The 2C horizon has hue of 2.5YR to 10YR, value of 6 to 8 and 4 to 7 moist, and chroma of 3 to 6. It typically is clay loam but is silt loam or silty clay loam in some pedons and contains 15 to 50 percent by volume of fragments of rock. It is slightly alkaline or moderately alkaline.
COMPETING SERIES: These are the Beartooth, Beeno, Bookcliff, Cortyzack, Dooley, Empedrado, Fairfield, Farnuf, Felor, Greenway, Gurney, Hangdo, Lefor, Lininger, Livona, Martinsdale, Moen, Reeder, Trag, Vida, Watrous, Wemple, Williams, and Yegen series. Beartooth soils have more than 35 percent rock fragments in the Bk horizons. Bookcliff soils have hard sandstone bedrock at a depth of 40 to 60 inches. Cortyzack soils have calcic horizons. Dooley, Greenway, Livona, Vida, and Williams soils have glacial till substratums. Empedrado, Felor, and Yegen soils have less than 15 percent coarse fragments in the underlying material. Fairfield and Martinsdale soils have a calcic horizon. Farnuf soils have a stratified substratum. Hangdo and Trag soils have carbonates at depths greater than 40 inches. Beeno, Gurney, Lefor, Lininger, Moen, Reeder, Watrous, and Wemple soils have bedrock at depths between 20 and 40 inches.
GEOGRAPHIC SETTING: Bullflat soils are nearly level to strongly sloping on open upland and valley parks in mountains at elevations of 3500 to 6200 feet. Slope gradients range from 0 to 15 percent. These soils formed in silty alluvial-colluvial materials weathered from sedimentary rocks. Mean annual temperature ranges from 37 to 45 degrees F. Mean annual precipitation ranges from 18 to 26 inches.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Gurney series and the Cordeston, Hilger, Paunsaugunt, Sawdust, and Vanocker series. Cordeston soils have a mollic epipedon more than 16 inches thick and are on the lower parts of the landscape. The Gurney soils are on higher parts of the landscape. The Hilger soils are skeletal and are on the outer margins of terraces. The Paunsaugunt soils are shallow to bedrock and are on higher convex parts of the landscape. The Sawdust and Vanocker soils are skeletal and are on timbered ridges and side slopes.
DRAINAGE AND PERMEABILITY: Well drained. Permeability is moderate and runoff is medium.
USE AND VEGETATION: Used mainly for grazing, wildlife and recreation. Native vegetation is western wheatgrass, junegrass, green needlegrass, blue grama, needleandthread, and sedges.
DISTIBUTION AND EXTENT: Mountainous areas of the Black Hills in South Dakota and Wyoming especially on the sedimentary rock formations and high terraces. The series is of moderate extent.
MLRA OFFICE RESPONSIBLE: Bismarck, North Dakota
SERIES ESTABLISHED: Custer County, South Dakota, 1985.
REMARKS: Diagnostic horizons and features recognized in this pedon are: mollic epipedon - the zone from the surface to a depth of about 10 inches (Ap, Bt1 horizons); argillic horizon - the zone from about 6 to 21 inches (Bt1, Bt2, Bt3 horizons).