LOCATION OPECHEKAHTA SD
Established Series
JWW
09/2011
OPECHEKAHTA SERIES
The Opechekahta series consists of deep to very deep, well drained soils that formed in colluvium derived primarily from limestone over residuum derived from red silty shale. Opechekahta soils are on escarpments and in canyons in foothills and mountains. Slopes range from 10 to 60 percent. Mean annual precipitation is about 510 mm and the mean annual temperature is about 7 degrees C.
TAXONOMIC CLASS: Fine-loamy, mixed, superactive, frigid Typic Calciustepts
TYPICAL PEDON: Opechekahta gravelly silt loam, on a northwest facing, concave slope of 40 percent in woodland at an elevation of about 1,205 meters. (Colors are for dry soil unless otherwise noted.) When described on September 1, 2005 the soil was dry throughout.
Oi--0 to 1 cm; slightly decomposed pine needles and shrubby and herbaceous plant residue. (0 to 2 cm thick)
A--1 to 6 cm; dark grayish brown (10YR 4/2) gravelly silt loam, very dark grayish brown (10YR 3/2) moist; weak medium and strong fine granular structure; soft, very friable, nonsticky and slightly plastic; many very fine and common fine and medium roots throughout; about 15 percent subangular and subrounded fine and medium limestone gravel; neutral; abrupt smooth boundary. (4 to 13 cm thick)
ABk--6 to 16 cm; grayish brown (10YR 5/2) gravelly silt loam, dark grayish brown (10YR 4/2) moist; weak medium and strong fine granular structure; soft, very friable, slightly sticky and slightly plastic; many very fine, common fine and medium roots throughout; about 20 percent subangular and subrounded fine and medium limestone gravel; finely dessiminated calcium carbonate throughout; strong effervescence; slightly alkaline; clear smooth boundary. (0 to 13 cm thick)
Bk1--16 to 38 cm; brown (10YR 5/3) gravelly silt loam, brown (10YR 4/3) moist; weak fine and medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine and common fine and medium and few coarse roots throughout; about 25 percent subangular and subrounded limestone fragments, of which 20 percent are gravel and 5 percent cobble; many medium distinct light brownish gray (10YR 6/2) spherical carbonate masses throughout; few fine distinct light gray (10YR 7/2) carbonate threads throughout; violent effervescence; moderately alkaline; clear smooth boundary. (15 to 38 cm thick)
2Bk2--38 to 57 cm; light reddish brown (5YR 6/3) gravelly silt loam, reddish brown (5YR 5/4) moist; weak fine and medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine, fine, and medium and few coarse roots throughout; about 30 percent subangular and subrounded limestone fragments, of which 25 percent are gravel and 5 percent cobble; many fine prominent pinkish white (7.5YR 8/2) carbonate threads throughout; common medium prominent pinkish white (7.5YR 8/2) spherical carbonate masses throughout; violently effervescent; moderately alkaline; clear wavy boundary. (15 to 46 cm thick)
2CBk--57 to 92 cm; light reddish brown (5YR 6/4) gravelly silt loam, reddish brown (5YR 5/4) moist; massive parting to thin and moderately thick, plate-like rock structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine and fine and few medium and coarse roots throughout; about 30 percent subangular and subrounded limestone fragments, of which 20 percent are gravel and 10 percent cobble; many medium prominent white (7.5YR 8/1) carbonate threads and spherical masses throughout; strong effervescence; moderately alkaline; clear smooth boundary. (0 to 38 cm thick)
3Ck--92 to 133 cm; red (2.5YR 5/6) silt loam, red (2.5YR 4/6) moist; massive with thin plate-like shale rock structure; slightly hard, friable, slightly sticky and slightly plastic; few very fine and fine roots between shale plates; common to many fine and medium prominent white (7.5YR 8/1) carbonate threads throughout; strong effervescence; moderately alkaline; gradual wavy boundary. (30 to 61 cm thick)
3Cr1--133 to 170 cm; red (2.5YR 5/6) highly fragmented silty shale; breaks into medium to very coarse, weakly to strongly cemented angular block-like rock fragments; few very fine and fine roots, primarily between blocks; continuous white (7.5YR 8/1) calcium carbonate coatings on blocks along fracture planes; slight effervescence; diffuse wavy boundary.
3Cr2--170 to 203 cm; red (2.5YR 5/6) weakly fragmented silty shale; breaks into coarse and very coarse, moderately to strongly cemented angular block-like rock fragments; very few white (7.5YR 8/1) calcium carbonate coatings on blocks along fracture planes; slight effervescence.
TYPE LOCATION: Lawrence County, South Dakota; about 2.5 miles west of Spearfish; located about 640 feet north and 2,100 feet east of the southwest corner of Sec. 6, T. 6 N., R. 2 E.; Chicken Creek USGS quadrangle; 44 degrees 30 minutes 18.6 seconds N. latitude and 103 degrees 55 minutes 21.3 seconds W. longitude; NAD 83.
RANGE IN CHARACTERISTICS:
Depth to calcic horizon and secondary calcium carbonate: 10 to 25 cm
Depth to lithologic discontinuity: typically 50 to 97 centimeters
Particle-size control section (weighted average):
Clay content: 18 to 35 percent
Sand content: 5 to 20 percent fine sand and coarser
Rock fragments: 10 to 35 percent subangular or subrounded limestone fragments, of which 10 to 30 percent are gravel or channers, 0 to 15 percent cobble, and 0 to 5 percent stones
A horizon:
Hue: 7.5YR or 10YR
Value: 4 or 5, 2 or 3 moist
Chroma: 1 to 3
Texture: L, SIL (fine-earth fraction)
Clay content: 15 to 27 percent
Rock fragments: 5 to 30 percent subangular and subrounded limestone fragments, of which 5 to 25 percent are gravel (non-flat) or channers (flat), and 0 to 5 percent cobble
Reaction: neutral or slightly alkaline
The ABk horizon, when present, has properties similar to the A horizon, except for reaction class, which is similar to the B
horizon.
Bk horizon:
Hue: 7.5YR or 10YR
Value: 5 to 7, 4 to 6 moist
Chroma: 2 to 4
Texture: L, CL, SIL, SICL (fine-earth fraction)
Clay content: 18 to 35 percent
Rock fragments: 10 to 35 percent subangular and subrounded limestone fragments, of which 10 to 30 percent are gravel or channers and 0 to 10 percent cobble
Calcium carbonate equivalent: 15 to 35 percent
Reaction: slightly alkaline or moderately alkaline
2Bk horizon:
Hue: 2.5YR to 7.5YR
Value: 5 to 7, 4 to 6 moist
Chroma: 2 to 6
Texture: L, CL, SIL, SICL (fine-earth fraction)
Clay content: 18 to 35 percent
Rock fragments: 10 to 35 percent subangular and subrounded limestone fragments, of which 10 to 30 percent are gravel or channers and 0 to 10 percent cobble
Calcium carbonate equivalent: 15 to 35 percent
Reaction: slightly alkaline to strongly alkaline
The 2CBk horizon, when present, has properties similar to the 2Bk horizon, except for structure, which is similar to the 3C
horizon.
3Ck horizon:
Hue: 10R to 5YR
Value: 5 to 7, 4 to 6 moist
Chroma: 3 to 6
Texture: SIL, SICL
Clay content: 18 to 35 percent
Rock fragments: 0 to 15 percent strongly cemented, angular or subangular shale fragments
Pararock fragments: 0 to 90 percent weakly to moderately cemented, angular or subangular shale fragments
Calcium carbonate equivalent: 5 to 20 percent
Reaction: moderately or strongly alkaline
3Cr horizon:
Hue: 10R to 5YR
Value: 5 to 7 dry, 4 to 6 moist
Chroma: 3 to 6
Texture: soft silty shale bedrock, typically slightly weathered and fractured in the upper 30 to 100 cm with less weathering with increasing depth
COMPETING SERIES:
Zahill - formed in loamy glacial till, does not have a lithologic discontinuity within 152 cm
GEOGRAPHIC SETTING:
Parent material: typically colluvium derived from limestone over residuum derived from red silty shale
Landform: backslopes of escarpments and hillslopes in canyons
Slopes: 10 to 60 percent
Elevation: 1,130 to 1,525 meters
Mean annual air temperature: 6 to 9 degrees
Mean annual precipitation: 460 to 610 mm
Precipitation pattern: In most years, half or more of the normal precipitation falls as rain and/or snow from April through
mid-July
Frost-free period: 100 to 140 days.
GEOGRAPHICALLY ASSOCIATED SOILS:
Citadel and
Citivar (T) - have fine-textured particle-size control sections; they generally occur on backslopes and footslopes
below Opechekahta soils
Rockerville - shallow to hard limestone; they occuron ridge crests above Opechekahta soils
Vanocker - has a thin argillic horizon, more than 35 percent rock fragments in the control section, and does not have a lithologic discontinuity in the series control section; they occur on similar landforms as Opechekahta soils
DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY: Well drained; medium to very rapid runoff; saturated hydraulic conductivity is moderately high
USE AND VEGETATION: Opechekahta soils are typically wooded and utilized for livestock grazing and wildlife habitat. The native vegetation consists of an overstory of ponderosa pine and bur oak; understory species include ground juniper, eastern hophornbean, western wheatgrass, Richardson needlegrass, and bluegrass.
DISTRIBUTION AND EXTENT: Low Limestone Plateau and Limestone Bench physiographic areas of the Black Hills of South Dakota; LRR G, MLRA 62 in South Dakota and Wyoming; the series is of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Denver, Colorado
SERIES PROPOSED: Proposed during the Update Soil Survey of Lawrence County, South Dakota. The name is coined from the geologic formations that contribute to the formation of this soil.
REMARKS:
Diagnostic horizons and features recognized in this pedon are:
Particle-size control section: The zone from 25 to 100 cm (Bk1, 2Bk2, 2CBk, and 3C horizons)
Ochric epipedon: The zone from 1 to 6 cm (A horizon)
Calcic horizon: The zone from 16 to 57 cm (Bk1 and 2Bk2 horizons)
Paralithic contact: The contact with red silty shale at 133 cm (3Cr1 and 3Cr2 horizons)
Lithologic discontinuity: At the upper boundary of the 2Bk2 horizon and at the upper boundary of the 3Ck horizon
The assignment of the cation-exchange activity class is inferred from lab data from similar soils in the surrounding area.
Opechekahta soils appear to have been previously mapped as Vanocker or Sawdust in other soil survey subsets of MLRA 62.
Taxonomic Version: Keys to Soil Taxonomy, Eleventh Ed., 2010
ADDITIONAL DATA:
National Cooperative Soil Survey
U.S.A.