LOCATION ROCKOA SD
Established Series
Rev. JK-KEC
12/2021
ROCKOA SERIES
The Rockoa series consists of very deep, well drained soils formed in colluvial material weathered from interbedded sandstone and shale on uplands. Slopes range from 2 to 60 percent. Mean annual precipitation is about 15 inches, and mean annual temperature is about 45 degrees F. Elevations range from about 2950 to 7000 feet.
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, frigid Glossic Hapludalfs
TYPICAL PEDON: Rockoa fine sandy loam, extremely stony - on a northeast-facing slope of 48 percent under ponderosa pine forest at 4800 feet elevation. When described the soil was moist throughout. (Colors are for dry soil unless otherwise stated).
Oi--0 to 1 inch; slightly decomposed leaves and roots. (0 to 2 inches thick)
A--1 to 6 inches; dark grayish brown (10YR 4/2) fine sandy loam, very dark grayish brown (10YR 3/2) moist; weak medium subangular blocky structure parting to fine and medium granular; soft, very friable; few fine to coarse roots; 20 percent by volume of stones and fragments of rock; neutral; abrupt wavy boundary. (2 to 5 inches thick)
E--6 to 11 inches; light brownish gray (10YR 6/2) fine sandy loam, dark grayish brown (10YR 4/2) moist; weak medium subangular blocky structure; soft, very friable; few fine roots; 30 percent by volume of stones and fragments of rock; neutral; clear wavy boundary. (3 to 10 inches thick)
B/E--11 to 16 inches; light brown (7.5YR 6/4) fine sandy loam, brown (7.5YR 5/4) moist (Bt); pinkish gray (7.5YR 7/2) fine sandy loam, brown (7.5YR 5/4) moist (E); moderate fine and medium subangular blocky structure; slightly hard, friable; few fine roots; 35 percent by volume of stones and fragments of rock; slightly acid; clear wavy boundary. (0 to 10 inches thick)
Bt1--16 to 22 inches; brown (7.5YR 5/4) sandy clay loam, dark brown (7.5YR 4/4) moist; moderate medium subangular blocky structure; hard, friable; few fine to coarse roots; 40 percent by volume of stones and fragments of rock; slightly acid; gradual wavy boundary.
Bt2--22 to 33 inches; brown (7.5YR 5/4) sandy clay loam, dark brown (7.5YR 4/4) moist; strong medium subangular blocky structure; hard, friable; few fine to coarse roots; 40 percent by volume of stones and fragments of rock; neutral; gradual wavy boundary. (Combined thickness of the Bt horizons is 10 to 25 inches.)
BC--33 to 52 inches; light brown (7.5YR 6/4) fine sandy loam, brown (7.5YR 5/4) moist; weak medium subangular blocky structure; hard, friable; few fine to coarse roots; 45 percent by volume of stones and fragments of rock; neutral; gradual wavy boundary. (0 to 20 inches thick)
C--52 to 60 inches; light brown (7.5YR 6/4) fine sandy loam, brown (7.5YR 5/4) moist; massive; hard, friable, few fine to coarse roots; 50 percent by volume of stones and fragments of rock; neutral.
TYPE LOCATION: Fall River County, South Dakota; about 6 miles west of Hot Springs; 160 feet east and 2570 feet south of the northwest corner of sec. 25, T. 7 S., R. 4 E.
RANGE IN CHARACTERISTICS: Carbonates are at a depth of 40 inches or below in some pedons. Many sandstone fragments ranging in size from coarse fragments up to boulders, about 12 feet in diameter are on the surface and mixed throughout the profile. They range from 15 to 55 percent by volume in the solum and 40 to 70 percent in the C horizon.
The A horizon has hue of 10YR, value of 2 to 5 and 2 or 3 moist, and chroma of 1 to 3 and 1 or 2 moist. It typically is fine sandy loam or sandy loam but some pedons are loam. It contains 0 to 40 percent by volume of stones, boulders, and coarse fragments of rock. It ranges from moderately acid to neutral.
The E horizon has hue of 10YR or 7.5YR, value of 5 to 7 and 4 or 5 moist, and chroma of 1 to 4. It typically is fine sandy loam, sandy loam or very fine sandy loam, but some pedons are loam. It contains 25 to 40 percent stones and fragments of rock. It ranges from moderately acid to neutral.
The B/E horizon has hue of 5YR, 7.5YR, or 10YR; value of 5 to 7 and 4 or 5 moist; and chroma of 2 to 4. It typically is fine sandy loam or sandy clay loam but some pedons are sandy loam, or loam. It contains 30 to 50 percent by volume of stones and fragments of rock. It ranges from moderately acid to neutral.
The Bt horizon has hue of 5YR, 7.5YR, or 10YR; value of 5 to 7 and 4 to 6 moist; and chroma of 3 to 6. It typically is sandy clay loam but some pedons are loam, clay loam or fine sandy loam and typically averages 18 to 30 percent clay. It contains 35 to 60 percent by volume of stones and fragments of rock. It ranges from moderately acid to neutral.
The BC horizon has hue of 5YR, 7.5YR, or 10YR; value of 6 or 7 and 5 or 6 moist; and chroma of 3 to 6. It typically is fine sandy loam but some pedons are sandy clay loam. It contains 35 to 65 percent by volume stones and fragments of rock. It ranges from moderately acid to neutral.
The C horizon has hue of 5YR, 7.5YR, or 10YR; value of 6 or 7 and 5 or 6 moist; and chroma of 3 to 6. It typically is fine sandy loam but some pedons are sandy clay loam or loam. It contains 40 to 70 percent by volume of stones and fragments of rock. It ranges from moderately acid to neutral. Sandstone, shale or limestone is between depths of 40 and 60 inches in some pedons.
COMPETING SERIES: These are the
Abreu,
Grizzly,
Macmeal,
Mocmont,
Pactola,
Tecolote,
Vanocker,
Wahatoya, and
Yourame series. Abreu and Macmeal soils contain smaller fragments and formed in materials from igneous rocks. Grizzly soils have thicker combined E and B/E horizons and contain more than 35 percent clay in the Bt horizon. Pactola soils contain more mica and formed in residuum from slate. Mocmont soils have fragments of rock that are dominantly angular pebbles. Tecolate soils receive more rainfall and formed in materials from felsite. Vanocker soils have carbonates at depths above 20 inches. Wahatoya soils have bedrock at a depth of 20 to 40 inches. Yourame soils have the base of the solum at depths greater than 60 inches.
GEOGRAPHIC SETTING: Rockoa soils are on hilly to very steep mountains at elevations of 2950 to 7000 feet. They have mainly north and east facing slopes or in protected cove-like positions in the landscape with a more favorable moisture regime. Slopes range from 6 to 60 percent. These soils formed in materials weathered from interbedded sandstone and shale. Mean annual temperature ranges from 39 to 48 degrees F, and the mean annual precipitation ranges from about 15 to 18 inches.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the
Butche and
Mathias soils. Mathias soils are on similar landscapes with south to southwest slope aspects. Mathias soils are mesic. Butche soils are shallow and typically are above the Rockoa soils.
DRAINAGE AND PERMEABILITY: Well drained. Runoff is medium to very rapid. Permeability is moderate.
USE AND VEGETATION: Used for timber production, recreation, wildlife and for some grazing. Native vegetation is dominantly a uniform stand of ponderosa pine with lesser amounts of cedar in some places. The understory is sparse amounts of shrubs and grasses.
DISTRIBUTION AND EXTENT: Of moderate extent in the Black Hills of western South Dakota and possibly adjoining western states.
SOIL SURVEY REGIONAL OFFICE (SSRO) RESPONSIBLE: Salina, Kansas
SERIES ESTABLISHED: Fall River County, South Dakota, 1980.
REMARKS: Diagnostic horizons and features recognized in this pedon are: ochric epipedon - the zone from surface to about 11 inches (A, E horizons); argillic horizon - the zone from 16 inches to about 33 inches (Bt1, Bt2 horizons). Depths were adjusted to account for the current standard of measuring O horizons. JCW 12/21.
National Cooperative Soil Survey
U.S.A.