LOCATION ROBANA WY+IDEstablished Series
TAXONOMIC CLASS: Fine-silty, mixed, superactive Pachic Argicryolls
TYPICAL PEDON: Robana silt loam, grassland. (Colors are for dry soil unless otherwise noted.)
A1--0 to 6 inches; dark grayish brown (10YR 4/2) silt loam, very dark brown (10YR 2/2) moist; moderate fine crumb structure; soft, very friable; neutral (pH 7.2); clear smooth boundary. (4 to 8 inches thick)
A2--6 to 15 inches; dark grayish brown (10YR 4/2) silt loam, very dark brown (10YR 2/2) moist; weak medium subangular blocky structure that parts to moderate medium granules; slightly hard, very friable; neutral (pH 7.0); clear smooth boundary. (4 to 12 inches thick)
AB--15 to 20 inches; brown (10YR 5/3) heavy silt loam, dark brown (10YR 3/3) moist; moderate medium prismatic structure that parts to moderate medium subangular blocks; hard, very friable; few clay films on faces of peds; neutral (pH 7.0); gradual smooth boundary. (4 to 8 inches thick)
Bt1--20 to 33 inches; brown (7.5YR 5/3) light silty clay loam, brown (7.5YR 4/3) moist; moderate fine prismatic structure that parts to strong fine angular and subangular blocks; hard, very friable; moderate continuous clay films on faces of peds; clay films in channels; distinct gray coatings of faces of peds; neutral (pH 7.0); gradual smooth boundary. (5 to 24 inches thick)
Bt2--33 to 52 inches; brown (7.5YR 5/3) light silty clay loam, brown (7.5YR 4/3) moist; moderate medium prismatic structure that parts to moderate subangular blocks; very hard, very friable; moderate continuous clay films in root channels; weak gray coating of bleached sand and silt; neutral (pH 7.0); gradual smooth boundary. (5 to 33 inches thick)
BC--52 to 60 inches; light yellowish brown (10YR 6/4) heavy silt loam, yellowish brown (10YR 5/4) moist; moderate medium subangular blocky structure; very hard, very friable; few clay films on faces of peds; scattered clay films in root channels; neutral (pH 7.0); gradual smooth boundary. (6 to 12 inches thick)
C--60 to 80 inches; light yellowish brown (10YR 6/4) silt loam, yellowish brown (10YR 5/4) moist; massive; hard, friable; neutral (pH 7.0).
TYPE LOCATION: Lincoln County, Wyoming; approximately 1,700 feet east of the northwest corner of sec. 35, T.35N., R.119W.
RANGE IN CHARACTERISTICS: The mollic epipedon is 16 to 36 inches thick, depth to calcareous material exceeds 60 inches, and the solum exceeds 50 inches thick. Organic carbon in the mollic epipedon ranges from about .8 to 3 percent and decreases uniformly with depth. The soil is 80 to 100 percent base-saturated. Content of coarse fragments is typically less than 1 percent and ranges from 0 to 5 percent. Mean annual soil temperature ranges from 32 degrees to 46 degrees F. and mean summer soil temperature ranges from 40 degrees to 58 degrees F. The
A horizon has hue of 2.5Y through 7.5YR, value of 4 or 5 dry and 2 or 3 moist and chroma of 1 through 3. It usually has granular or crumb primary structure, but has subangular blocky structure in some pedons. This horizon is soft to slightly hard and slightly acid to slightly alkaline.
The Bt horizon has hue of 2.5Y through 7.5YR, value of 5 or 6 dry and 3 through 5 moist and chroma of 2 through 4. It usually has prismatic primary structure but has subangular blocky structure in some pedons. This horizon is usually heavy silt loam or light silty clay loam, but clay ranges from 18 to 35 percent, silt from 40 to 70 percent, and sand from 5 to 30 percent with less than 15 percent fine or coarser sand. It is slightly acid to slightly alkaline.
The C horizon has hue of 2.5Y through 7.5YR. It is slightly acid to mildly alkaline.
COMPETING SERIES: These are the Bozeman, Greybo, Halfcircle, Lanark and Pinebutte series. Bozeman soils have continuous horizons of secondary carbonate accumulation. Greybo soils have horizons containing lamellae. Halfcircle soils are deep to a paralithic contact. Lanark soils have a calcic horizon. Pinebutte soils are deep to a lithic contact.
GEOGRAPHIC SETTING: Robana soils are on gently to moderately sloping upland hills and ridges. Slopes usually range from 0 to about 15 percent. These soils formed in thick noncalcareous or weakly calcareous aeolian parent materials. At the type location the average annual precipitation is 18 inches with nearly equal amounts of precipitation occurring during most months. The mean annual temperature is 39 degrees F., and the mean summer temperature is 58 degrees F.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Buckskin soils and the competing Bozeman soils. Buckskin soils have mollic epipedons less than 16 inches thick.
DRAINAGE AND PERMEABILITY: Well-drained; medium runoff; moderate permeability.
USE AND VEGETATION: These soils used as irrigated or dry cropland and as native pastureland. Principal native plants are native bluegrass, clover and big sage.
DISTRIBUTION AND EXTENT: Western portion of Wyoming. The series is of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Star Valley Area, Idaho and Wyoming. 1971.