LOCATION OPAL SDEstablished Series
TAXONOMIC CLASS: Fine, smectitic, mesic Leptic Haplusterts
TYPICAL PEDON: Opal clay - on convex, northeast-facing slope of 1 percent under native grass. (Colors are for dry soil unless otherwise stated)
A--0 to 2 inches; grayish brown (10YR 5/2) clay, very dark gray (10YR 3/1) moist; moderate medium and fine granular structure; slightly hard, friable, sticky and plastic; many fine and medium roots; slightly alkaline; clear smooth boundary. (2 to 8 inches thick)
Bss1--2 to 10 inches; grayish brown (2.5Y 5/2) clay, very dark grayish brown (2.5Y 3/2) moist; moderate medium and coarse subangular blocky structure; very hard, firm, very sticky and very plastic; many fine and medium roots; common distinct nonintersecting slickensides; cracks 1/2 inch wide; 1 percent pebbles; slight effervescence; neutral; clear wavy boundary.
Bss2--10 to 16 inches; grayish brown (2.5Y 5/2) clay, very dark grayish brown (2.5Y 3/2) moist; weak coarse prismatic structure parting to moderate medium and coarse subangular blocky; extremely hard, firm, very sticky and very plastic; common fine and medium roots; many prominent intersecting slickensides; cracks 1 inch wide; 1 percent pebbles; strong effervescence; moderately alkaline; clear wavy boundary. (Combined Bss horizons 8 to 20 inches thick)
Bkss--16 to 26 inches; light brownish gray (2.5Y 6/2) clay, dark grayish brown (2.5Y 4/2) moist; weak coarse prismatic structure parting to moderate medium and coarse subangular blocky; extremely hard, firm, very sticky and very plastic; few fine roots; many prominent intersecting slickensides; cracks 1/2 to 1 inch wide; many fine and medium accumulations of carbonate; 1 percent pebbles; strong effervescence; moderately alkaline; clear wavy boundary. (0 to 15 inches thick)
Cyz1--26 to 30 inches; light brownish gray (2.5Y 6/2) clay, dark grayish brown (2.5Y 4/2) moist; many fine distinct yellowish brown (10YR 5/6) mottles; massive; very hard, firm, very sticky and very plastic; many fine nests of gypsum and other salts; 1 percent pebbles; strong effervescence; moderately alkaline; clear wavy boundary.
Cyz2--30 to 35 inches; light brownish gray (2.5Y 6/2) clay, dark grayish brown (2.5Y 4/2) moist; few fine prominent strong brown (7.5YR 5/6) and common fine distinct yellowish brown (10YR 5/6) mottles; massive; hard, friable, very sticky, and very plastic; 55 percent soft shale fragments; many fine and medium nests of gypsum and other salts; strong effervescence; moderately alkaline; clear wavy boundary.
Cr1--35 to 41 inches; light brownish gray (2.5Y 6/2) and dark gray (5Y 4/1) soft shale, dark grayish brown (2.5Y 4/2); moist; common fine prominent strong brown (7.5YR 5/6) mottles; many yellowish brown (10YR 5/6) iron stains in cracks and seams; many fine nests of gypsum and other salts; strong effervescence; slightly alkaline; gradual wavy boundary.
Cr2--41 to 60 inches; light brownish gray (2.5Y 6/2) and dark gray (5Y 4/1) soft shale, dark grayish brown (2.5Y 4/2) moist; common fine prominent strong brown (7.5YR 5/6) mottles; many yellowish brown (10YR 5/6) iron stains along seams and cracks; few fine nests of salts; slightly alkaline.
TYPE LOCATION: Jones County, South Dakota; about 2 miles east and 1 mile north of Murdo; 2508 feet south and 1585 feet east of the northwest corner, sec. 28, T. 1 S., R. 29 E.
RANGE IN CHARACTERISTICS: The depth to soft shale is typically 28 to 35 inches and ranges from 20 to 40 inches. Cracks 1/2 to one inch wide and several feet long extend downward through the solum when the soil is dry. The depth to carbonates ranges from 0 to 8 inches. Pebbles range from 0 to 5 percent, by volume, throughout the solum.
The A horizon has hue of 10YR, 2.5Y or 5Y, value of 4 or 5 and 2 or 3 moist, and chroma of 1 or 2. It is typically clay but some pedons are silty clay. It is neutral or slightly alkaline. Some pedons have a thin, fragile surface crust or mulch.
The Bss horizon has hue of 2.5Y or 5Y, value of 4 to 6 and 2 to 4 moist, and chroma of 2 or 3. It is extremely hard or very hard when dry and extremely firm to firm when moist. It averages from 60 to 70 percent clay. It ranges from neutral to moderately alkaline.
The Bkss horizon has hue of 2.5Y or 5Y, values of 4 to 6 and 3 to 5 moist, and chroma of 2 to 4. It averages from 60 to 70 percent clay. It is slightly alkaline or moderately alkaline and has few to many accumulations of carbonate in most pedons.
The C horizon has hue of 2.5Y or 5Y, values of 5 or 6 and 4 or 5 moist, and chroma of 1 to 3. It contains 1 to 60 percent, pebbles or soft shale fragments by volume. Reaction ranges from slightly acid to moderately alkaline. It has an EC of 2 mmhos/cm or more.
The Cr horizon is soft shale and ranges from strongly acid to moderately alkaline.
COMPETING SERIES: This is the Boyd series. Boyd soils have less than 60 percent clay in the Bss horizons.
GEOGRAPHIC SETTING: Opal soils are on level to moderately steep uplands. Surfaces are plane or convex, and slope gradients range from 0 to 25 percent. Gilgai microrelief is on most landscapes. Opal soils formed in residuum or locally transported clay sediments weathered from soft shales. Mean annual air temperatures is 44 to 49 degrees F. and mean annual precipitation ranges from about 16 to 20 inches. Growing season is 130 to 140 days; average growing season precipitation is 12 to 16 inches; and growing degree days are 2700 to 3300 degree days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Bullcreek, Chantier, Dupree, Hurley, Labu, Lakoma, Promise and Sansarc soils. Bullcreek and Promise soils are on toeslopes and flats below the Opal soils. They are more than 40 inches deep to shale. Chantier soils are on steeper landscapes. They do not have mollic epipedons and contain more salts. Dupree and Sansarc soils typically are on steeper areas on the landscape. They have bedrock at depths of 10 to 20 inches. Hurley soils are on less sloping landscapes. They have a natric horizon. Lakoma and Labu soils are on similar landscapes. They do not have a mollic epipedon or intersecting slickensides.
DRAINAGE AND PERMEABILITY: Well drained. Runoff is medium to very high depending on slope. Permeability is very slow. After periods of drought the initial intake may be rapid due to the cracks.
USE AND VEGETATION: Cropland and native range. Winter wheat, alfalfa, and sorghum are the principal crops. Native vegetation is mainly western wheatgrass, green needlegrass, blue grama, sideoats grama, and sedges.
DISTRIBUTION AND EXTENT: Of large extent in central South Dakota, mostly west of the Missouri River.
MLRA OFFICE RESPONSIBLE: Bismarck, North Dakota
SERIES ESTABLISHED: Hughes County, South Dakota, 1970.
REMARKS: Diagnostic horizons and features recognized in this pedon are: mollic epipedon - the zone from the surface of the soil to a depth of 16 inches (A, Bss1 and Bss2 horizons).
ADDITIONAL DATA: NSSL data 85PO042-85P0049 and 85PO050-85PO056.