LOCATION ST. ONGE SDEstablished Series
TAXONOMIC CLASS: Fine-loamy, mixed, superactive, mesic Cumulic Haplustolls
TYPICAL PEDON: St. Onge loam - cultivated. When described the soil was irrigated. (Colors are for dry soil unless otherwise stated.)
Ap--0 to 7 inches; dark grayish brown (10YR 4/2) loam, very dark brown (10YR 2/2) moist; weak very fine and fine granular structure; hard, friable; strong effervescence; slightly alkaline; abrupt smooth boundary.
A--7 to 17 inches; very dark grayish brown (10YR 3/2) silt loam, black (10YR 2/1) moist; weak coarse and medium subangular blocky structure; hard, friable; strong effervescence; slightly alkaline; clear wavy boundary. (Combined A horizons is 10 to 25 inches thick.)
Bw--17 to 24 inches; dark grayish brown (10YR 4/2) loam, very dark brown (10YR 2/2) moist; weak medium prismatic structure parting to weak medium and coarse subangular blocky structure; hard, friable; few fine accumulations of carbonate; strong effervescence; slightly alkaline; clear wavy boundary. (0 to 15 inches)
Bk1--24 to 32 inches; brown (7.5YR 5/4) loam, dark brown (7.5YR 4/4) moist; weak medium prismatic structure; hard, friable; common fine accumulations of carbonates; strong effervescence; slightly alkaline; gradual wavy boundary.
Bk2--32 to 42 inches; light brown (7.5YR 6/4) loam, dark brown (7.5YR 4/4) moist; massive; hard, friable; many fine accumulations of carbonate; violent effervescence; slightly alkaline; gradual wavy boundary. (Combined Bk horizons is 10 to 25 inches thick.)
C1--42 to 52 inches; brown (7.5YR 5/4) fine sandy loam, dark brown (7.5YR 4/4) moist; massive; soft, very friable; common fine accumulations of carbonate; strong effervescence; slightly alkaline; clear wavy boundary.
C2--52 to 60 inches; brown (10YR 5/3) silt loam, dark brown (10YR 4/3) moist; massive; hard, friable; many fine accumulations of carbonate; violent effervescence; slightly alkaline.
TYPE LOCATION: Lawrence County, South Dakota; about 6 miles north and 1 miles east of Spearfish; 2900 feet west and 1100 feet south of the northeast corner of sec. 11, T. 7 N., R. 2 E.
RANGE IN CHARACTERISTICS: The thickness of the mollic epipedon ranges from 20 to more than 40 inches. Typically, depth to free carbonates range from 0 to 10 inches, but some pedons are leached to depths of 15 inches. The series control section is loam, silt loam or clay loam and averaging between 18 and 30 percent clay and more than 15 percent fine or coarser sand. Strata of coarser textured materials are in some pedons. Some pedons have buried horizons below depths of 50 inches.
The A horizon has hue of 10YR, value of 3 to 5 and 2 or 3 moist, and chroma of 1 to 3. It is loam, silt loam, or very fine sandy loam. It is neutral or slightly alkaline.
The Bw horizon has hue of 10YR or 7.5YR, value of 3 to 5 and 2 to 4 moist, and value of 1 to 3. It is loam, silt loam or clay loam. It ranges from neutral to moderately alkaline. Some pedons have no accumulation of carbonate.
The Bk horizon has hue of 5YR to 10YR, value of 5 or 6 and 4 to 5 moist, and chroma of 2 to 4. It is loam, silt loam or clay loam. It has common or many accumulations of carbonate. It is slightly or moderately alkaline.
The C horizon has 5YR to 10YR hue, value of 5 or 6 and 4 or 5 moist, and chroma of 2 to 4. The C horizon typically contains strata of loam, fine sandy loam, silt loam, very fine sandy loam, and clay loam. It is slightly or moderately alkaline. Most pedons have few to many threads of carbonates. Faint yellow and brown mottles are below depths of 40 inches in some pedons. A few coarse fragments are in some pedons.
COMPETING SERIES: These are the Bon, Draper, Humbarger, Lynx, Manzano, Maskell, Merrick, Pack and Shanta series. The Bon soils receive more precipitation. The Davis, Draper, Lynx, Manzano, Maskell, Merrick, and Pack are leached of carbonates to depths greater than 15 inches. The Humbarger soils have a higher mean annual temperature. The Shanta soils contain from 5 to 20 percent by volume coarse fragments throughout the series control section.
GEOGRAPHIC SETTING: The St. Onge soils are on nearly level stream terraces, flood plains, and fans with slope gradients of 0 to 2 percent. The St. Onge soils formed in calcareous, stratified, loamy alluvium. Mean annual temperature ranges from 43 to 50 degrees F, and precipitation ranges from 14 to 20 inches.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Swint and Tilford soils and the Barnum, Haverson, Keith, Nevee, Satanta and Vale soils. Barnum and Haverson soils do not have a mollic epipedon and are below the St. Onge soils. Keith, Nevee, Satanta, Swint, and Tilford soils are on higher landscapes. The Swint and Tilford soils have a mollic epipedon less than 20 inches thick. Keith and Satanta soils have an argillic horizon and Nevee soils do not have a mollic epipedon. Vale soils typically are on higher landscapes and have an argillic horizon.
DRAINAGE AND PERMEABILITY: Well drained or moderately well drained; low runoff; moderate permeability. These soils are occasionally flooded.
USE AND VEGETATION: Soils are both cultivated and in native rangeland. Alfalfa, corn, and small grain are the principal crops. The native vegetation is mid and tall grasses; mainly western wheatgrass, little bluestem, switchgrass, and big bluestem.
DISTRIBUTION AND EXTENT: Of moderate extent in the foothills of the Black Hills in western South Dakota.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Denver, Colorado
SERIES ESTABLISHED: Meade County, South Dakota, 1974.
REMARKS: Diagnostic horizons and features recognized in this pedon are: mollic epipedon - the zone from the surface of the soil to a depth of about 24 inches (Ap, A, Bw horizon).