LOCATION SNOMO              SD+WY
Established Series
Rev. PRJ-FTM-KEC
11/2003

SNOMO SERIES


The Snomo series consists of deep or very deep, well drained soils formed in clayey materials weathered from acid shale on the uplands. These soils have moderate permeability. Slopes range from 2 to 20 percent. Mean annual precipitation is about 17 inches and mean annual air temperature is about 45 degrees F.

TAXONOMIC CLASS: Very-fine, smectitic, mesic Torrertic Dystrustepts

TYPICAL PEDON: Snomo clay - on a 8 percent north-facing slope in scattered trees with native grass understory. (Colors are for dry soil unless otherwise stated.)

A1--0 to 2 inches; light gray (10YR 6/1) silty clay, very dark grayish brown (10YR 3/2) moist; weak thick platy structure parting to weak fine granular; hard, friable, slightly sticky and slightly plastic; many fine and medium roots; slightly acid; clear smooth boundary.

A2--2 to 5 inches; light gray (10YR 6/1) clay, very dark grayish brown (10YR 3/2) moist; weak fine subangular blocky structure; hard, friable, sticky and plastic; common fine roots; moderately acid; clear smooth boundary. (Combined A horizons 4 to 8 inches thick)

Bw1--5 to 14 inches; light brownish gray (10YR 6/2) clay, very dark grayish brown (10YR 3/2) moist, rubbed dark grayish brown (10YR 4/2) moist; weak coarse prismatic structure parting to weak medium and fine subangular blocky; very hard, friable, sticky and plastic; common fine roots; strongly acid; clear smooth boundary.

Bw2--14 to 28 inches; pale brown (10YR 6/3) clay, dark brown (10YR 3/3) moist, rubbed brown (10YR 4/3) moist; weak coarse prismatic structure parting to weak medium subangular blocky; hard, friable, sticky and plastic; few fine roots; few fine fragments of shale; very strongly acid; clear wavy boundary. (Combined Bw horizons 20 to 35 inches thick)

BC--28 to 38 inches; pale brown (10YR 6/3) clay, dark grayish brown (10YR 4/2) moist; common fine and medium distinct mottles of yellowish brown (10YR 5/6) and strong brown (75.YR 5/6); weak coarse subangular blocky structure; hard, friable, sticky and plastic; few fine roots; many fine fragments of shale; extremely acid; gradual smooth boundary. (0 to 15 inches thick)

C1--38 to 45 inches; pale brown (10YR 6/3) clay, brown (10YR 4/3) moist; few fine distinct mottles of yellow (2.5Y 8/6) massive; slightly hard, friable, sticky and plastic; few fine roots; many fine fragments of shale, extremely acid; abrupt wavy boundary.

C2--45 to 50 inches; very pale brown (2.5Y 7/3) and yellow (5Y 8/6) clay, light olive brown (2.5Y 5/3) and yellow (5Y 7/6) moist; massive; slightly hard, friable, sticky and plastic; many coarse fragments of brittle shale; extremely acid; clear wavy boundary.

Cr--50 to 60 inches; gray (10YR 5/1) acid shale, black (N 2/) moist; yellow (5Y 8/6) and yellowish red (5YR 5/8) coatings on fracture faces of shale.

TYPE LOCATION: Butte County, South Dakota; 8 miles east and 2 miles south of Belle Fourche; 2440 feet north and 115 feet east of the southwest corner of sec. 19, T. 8 N., R. 4 E.

RANGE IN CHARACTERISTICS: Bedded shale typically is between a depth of 40 and 60 inches but is below 60 inches in some pedons. Colors throughout the soil are inherent to the shale.

The A horizon has hue of 10YR, value of 5 to 7 and 3 or 4 moist, and chroma of 1 or 2. It is silty clay or clay and contains 0 to 15 percent by volume of fine fragments of shale less than 3 mm in size. It is extremely acid to slightly acid. Some pedons have a thin distinct E horizon as evidenced by prominent clean silt and sand grains.

The Bw horizon has hue of 10YR, 2.5Y, and 7.5YR, value of 5 or 6 and 3 or 4 moist, and chroma of 2 to 4. Moist value typically is one unit higher when rubbed. It has 0 to 20 percent by volume of fine fragments of shale less than 3 mm in size. It is strongly acid to extremely acid.

The BC and C horizons have hue of 10YR or 2.5Y, value of 5 or 6 and 3 to 5 moist, and chroma of 1 to 3. Moist value typically is one unit higher when rubbed. They have 15 to 50 percent by volume of fine to coarse fragments of shale ranging from 1 to 25 mm in size. They are very strongly acid or extremely acid.

The Cr horizon is multicolored in hue of 10YR, 2.5Y, or 5Y; and is very hard and brittle but has a hardness of less than 3 on the Moh's scale of hardness. It is very strongly acid or extremely acid.

COMPETING SERIES: There are no other series in the same family.

GEOGRAPHIC SETTING: Snomo soils are on gently sloping to moderately steep uplands. Slope gradients range from 2 to 20 percent. The soil formed in clayey materials weathered from acid shale. Mean annual temperature ranges from 43 to 48 degrees F, and precipitation from 14 to 18 inches.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Graner and Grummit soils. Graner soils are on similar positions as the Snomo soil. They do not have a cambic horizon. Grummit soils are on adjacent steeper slopes and have bedded shale within depths of 20 inches.

DRAINAGE AND PERMEABILITY: Well drained. Surface runoff is very low to medium depending on slope. Permeability is moderate.

USE AND VEGETATION: These soils are used primarily as native rangeland. Principal native vegetation includes sunsedge, western wheatgrass, prairie leadplant, little bluestem, big bluestem, bur oak, and ponderosa pine.

DISTRIBUTION AND EXTENT: Western South Dakota. The series is of moderate extent.

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 are: ochric epipedon - the zone from the surface of the soil to a depth of about 5 inches (A1 and A2 horizons); cambic horizon - the zone from a depth of about 5 to 28 inches (Bw1 and Bw2 horizons).

ADDITIONAL DATA: Lincoln lab data nos. 70L428-70L435 is available.


National Cooperative Soil Survey
U.S.A.