LOCATION SHELLCREEK WYEstablished Series
TAXONOMIC CLASS: Fine, smectitic, frigid Ustertic Haplocambids
TYPICAL PEDON: Shellcreek silty clay-rangeland. (Colors are for dry soil unless otherwise stated.)
A1--0 to 1 inch; light gray (5Y 7/2) silty clay, light olive brown (2.5Y 5/4) moist; moderate fine and medium platy structure, upper 1/4-inch a soft, fragile crust; soft, friable, very sticky and very plastic; few very fine roots; strongly effervescent, lime disseminated; strongly alkaline (pH 8.8); abrupt smooth boundary.
A2--1 to 3 inches; light olive gray (5Y 6/2) silty clay, olive brown (2.5Y 4/4) moist; moderate very fine granular structure; soft, friable, very sticky and very plastic; few very fine roots; strongly effervescent, lime disseminated; very strongly alkaline (pH 9.1); clear wavy boundary. (A horizon is 1 to 6 inches thick)
Bw1--3 to 5 inches; pale olive (5Y 6/3) silty clay, olive brown (2.5Y 4/4) moist; weak coarse prismatic structure parting to moderate coarse angular blocky; extremely hard, very firm, very sticky and very plastic; few fine roots; strongly effervescent, lime disseminated and as few filaments in root channels; very strongly alkaline (pH 9.2); clear smooth boundary.
Bw2--5 to 20 inches; pale olive (5Y 6/3) silty clay, olive brown (2.5Y 4/4) moist; weak coarse prismatic structure parting to moderate fine and medium subangular blocky; extremely hard, firm, very sticky and very plastic; few fine roots; strongly effervescent, lime disseminated and as few isolated specks along root channels; very strongly alkaline (pH 9/2); clear smooth boundary. (Bw horizon is 8 to 21 inches thick)
Bk--20 to 24 inches; pale olive (5Y 6/3) silty clay, olive brown (2.5Y 4/4) moist; weak fine and medium subangular blocky structure; extremely hard, firm, very sticky and very plastic; strongly effervescent in matrix, violently effervescent where secondary carbonates occur as common soft masses and filaments; few fine nests of salts and sulfates; very strongly alkaline (pH 9.2); diffuse wavy boundary. (0 to 22 inches thick)
C--24 to 60 inches; pale olive (5Y 6/3) silty clay, olive brown (2.5Y 4/4); massive with fine and medium subangular fragments; extremely hard, firm, very sticky and very plastic; strongly effervescent, lime disseminated; very strongly alkaline (pH 9.2).
TYPE LOCATION: Sweetwater County, Wyoming; about 1,200 feet west, 250 feet south of the east quarter corner of sec. 5, T. 25 N., R 105 W.
RANGE IN CHARACTERISTICS: Depth to bedrock exceeds 60 inches. The mean annual soil temperature is about 43 to 47 degrees F., and the mean summer soil temperature is 59 to 63 degrees F. The particle size control section is clay, heavy clay loam, silty clay, and heavy silty clay loam with 35 to 60 percent clay and 45 percent or less total sand. Rock fragments are uncommon but may range up to 5 percent rounded pebbles. Some pedons have a thin lag gravel on the surface.
The A horizon has hue of 5Y through 10YR, value of 5 through 7 dry, 4 through 6 moist, and chroma of 2 through 4. EC ranges from 2 to 8 mmhos. ESP ranges from 4 to 20. Reaction is moderately through very strongly alkaline.
The Bw horizon has hue of 5Y through 10YR, value of 5 through 7 dry, 4 or 5 moist, and chroma of 2 through 4. Texture is clay, silty clay, heavy clay loam, or heavy silty clay loam. EC ranges from 2 to 8 mmhos. ESP ranges from 8 to 23. Reaction is moderately through very strongly alkaline.
The Bk horizon, when present, has the same color and texture range as the Bw horizon except that moist value may be 6. The secondary carbonates are expressed weakly in most pedons because of the fine nature of the soil fabric so the identification of a Bk is difficult in some pedons. EC ranges from 4 to 8 mmhos in most pedons but may range to 16 where salts more soluble than gypsum are present. ESP ranges from 8 to 23. Reaction ranges from moderately through very strongly alkaline.
The C horizon has hue of 5Y through 10YR, value of 5 or 6 dry, 4 or 5 moist, and chroma of 2 through 4. Texture is clay, 3 - Shellcreek Series
silty clay, heavy clay loam, and heavy silty clay loam. EC ranges from 4 to 16 mmhos. ESP ranges from 8 to 30. Reaction is moderately through very strongly alkaline.
COMPETING SERIES: There are no other series presently identified in this class.
GEOGRAPHIC SETTING: Shellcreek soils are on terraces, alluvial fans, fan aprons, and in depressional areas. These soils formed in fine textured alluvium derived from clay shale with some influence from interbedded siltstone. Slopes are simple and range from 0 to 3 percent. Elevation is 6,500 to 7,200 feet. The mean annual precipitation ranges from 7 to 10 inches of which about half falls as predominantly snow with some rain in April, May, and early June. The mean annual temperature ranges from 36 to 42 degrees F. The frost-free season is estimated to range from 60 to 90 days depending upon elevation, aspect, and local air drainage.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Debone and Farson soils. Debone soils have natric horizons. Farson soils are coarse-loamy, have argillic horizons, and occur on contiguous uplands.
DRAINAGE AND PERMEABILITY: Moderately well drained; slow runoff. Some areas receive runon water from surrounding areas and have local flooding or ponding for short durations of two weeks in March through May. Permeability is very slow.
USE AND VEGETATION: Rangeland and wildlife habitat with minor areas of irrigated hayland and small grain. Native vegetation is thickspike wheatgrass, bottlebrush squirreltail, big sagebrush, and Indian ricegrass on the nonsodic areas and Gardner saltbush and greasewood dominations as shrubs in the sodic areas.
DISTRIBUTION AND EXTENT: Cold, high basins of southwestern Wyoming. The series is of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Eden Valley Soil Survey Area, Sweetwater County, Wyoming; 1985.