LOCATION ACHIMIN WAEstablished Series
TAXONOMIC CLASS: Fine, mixed, superactive, mesic Typic Palexerolls
TYPICAL PEDON: Achimin silt loam - on a northeast-facing, 29 percent slope, at an elevation of 2,590 feet under grass vegetation. (Colors are for dry soil unless otherwise noted. All textures are apparent field textures)
A1--0 to 7 inches; brown (10YR 4/3) silt loam, very dark brown (10YR 2/2) moist; weak very fine subangular blocky structure; soft, very friable, slightly sticky, slightly plastic; many very fine and fine roots; 5 percent pebbles; neutral (pH 6.6); gradual smooth boundary.
A2--7 to 18 inches; brown (10YR 4/3) silt loam, very dark brown (10YR 2/2) moist; weak fine subangular blocky structure; slightly hard, friable, sticky, slightly plastic; many very fine and common fine roots; 5 percent pebbles; neutral (pH 7.2); clear smooth boundary. (Combined thickness of the A horizon is 10 to 18 inches)
Bt1--18 to 24 inches; yellowish brown (10YR 5/4) silty clay loam, dark yellowish brown (10YR 3/4) moist; moderate fine subangular blocky structure; hard, friable, sticky, plastic; common very fine roots; common moderately thick brown (10YR 4/3) clay films on faces of peds; 5 percent pebbles; mildly alkaline (pH 7.8); abrupt smooth boundary. (6 to 9 inches thick)
2Bt2--24 to 29 inches; dark yellowish brown (10YR 4/6) silty clay loam, dark yellowish brown (10YR 3/4) moist; moderate fine angular blocky structure; hard, firm, sticky, plastic; few very fine roots; many moderately thick brown (10YR 4/3) clay films on faces of peds; 2 percent pebbles; moderately alkaline (pH 8.0); clear smooth boundary. (0 to 13 inches thick)
2Bt3--29 to 34 inches; yellowish brown (10YR 5/6) silty clay loam, dark yellowish brown (10YR 4/6) moist; massive; slightly hard, friable, sticky, plastic; few thin brown (10YR 4/3) clay films or faces of peds; moderately alkaline (pH 8.0); abrupt smooth boundary. (0 to 5 inches thick)
2Bk1--34 to 40 inches; yellowish brown (10YR 5/6, 70 percent) very pale brown (10YR 7/4, 30 percent) heavy silt loam, dark yellowish brown (10YR 4/6) moist; massive; slightly hard, very friable, sticky, plastic; strongly effervescent; moderately alkaline (pH 8.0); abrupt smooth boundary. (0 to 5 inches thick)
2Bk2--40 to 48 inches; pale yellow (2.5Y 7/4) heavy silt loam, light olive brown (2.5Y 5/6) moist; massive; slightly hard, friable, sticky, slightly plastic; common fine lime filaments; strongly effervescent; moderately alkaline (pH 8.0); gradual smooth boundary. (0 to 20 inches thick)
2Bk3--48 to 60 inches; pale yellow (2.5Y 7/4) silt loam, light olive brown (2.5Y 5/6) moist; massive; slightly hard, friable, slightly sticky, slightly plastic; few fine lime filaments; slightly effervescent; moderately alkaline (pH 8.0).
TYPE LOCATION: Colville Indian Reservation; Okanogan County, Washington; about 18 miles west of the town of Nespelem; 2,100 feet south and 600 feet west of the northeast corner of sec. 31, T. 31 N., R. 28 E., W.M.
RANGE IN CHARACTERISTICS: The mean annual soil temperature at a depth of 20 inches ranges from 49 to 51 degrees F. These soils are usually moist but are dry in all parts between depths of 4 and 12 inches for 90 to 105 consecutive days following the summer solstice. The mollic epipedon is 10 to 18 inches thick. The particle-size control section is 35 to 45 percent clay and 0 to 5 percent pebbles.
The A horizon has value of 4 or 5 dry, 2 or 3 mo ist, and chroma of 2 or 3 dry or moist. It is 0 to 5 percent pebbles.
Some pedons have thin E horizon.
The Bt horizon has value of 4 through 6 dry, 3 through 5 moist, and chroma of 4 through 6 dry or moist. It is heavy silty clay loam, or silty clay. It is 0 to 5 percent pebbles. Reaction is mildly alkaline or moderately alkaline.
The 2Bt horizon has hue of 10YR or 2.5Y, value of 4 or 5 dry, 3 or 4 moist, and chroma of 4 through 6 dry or moist. It is silty clay loam or silty clay. It is 0 to 5 percent pebbles. Reaction is mildly alkaline or moderately alkaline. Some pedons do not have a 2Bt horizon. Some pedons have a 2Btk horizon.
The 2Bk horizon has hue of 10YR or 2.5Y, value of 5 through 7 dry, 4 or 5 moist, and chroma of 3 through 6 dry or moist. It is silt loam or heavy silt loam. It is 0 to 5 percent pebbles. Reaction ranges from mildly alkaline to strongly alkaline. Some pedons have a 2C horizon.
COMPETING SERIES: These are the Coleman, Dry Creek, Pomponio, Pritchard, and Tutuilla series in other families. All of these soils are in a montmorillonitic family. In addition, Coleman soils are 5 to 15 percent rounded pebbles in the particle-size control section and are moderately acid in the A horizon. Dry Creek soils are cobbly throughout the particle-size control section.
GEOGRAPHIC SETTING: Achimin soils are on toeslopes, footslopes, and backslopes of foothills adjacent to basalt plateaus and in depressions on till plains. These soils formed in loess overlying siltstone residuum. Slopes are 0 to 60 percent. Elevations range from 1,500 to 2,600 feet. The climate is characterized by warm, dry summers and cool, moist winters. The average annual precipitation is 12 to 15 inches. The mean January temperature is about 25 degrees F, the mean July temperature is about 71 degrees F, and the mean annual temperature is about 48 degrees F. The frost-free season is 110 to 150 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Anders, Badge, Bakeoven, Conconully, Farrell, Ginnis (T), Picard, and Timentwa. Anders soils have a lithic contact at 20 to 40 inches. Badge soils are loamy-skeletal. Bakeoven soils are very shallow. Conconully, Farrell, Ginnis, Picard, and Timentwa soils soils are coarse-loamy. In addition, Farrell soils are in an aridic moisture regime. Ginnis soils have a paralithic contact at 20 to 40 inches. Timentwa soils have a mollic epipedon more than 20 inches thick.
DRAINAGE AND PERMEABILITY: Well drained, slow to very rapid runoff;
moderate permeability in the surface, moderately slow to slow permeability in the subsoil.
USE AND VEGETATION: Livestock grazing, dryland cropland, wildlife habitat and watershed are the principal uses. Native vegetation includes bluebunch wheatgrass, Idaho fescue, Sandberg bluegrass, arrowleaf balsamroot, common yarrow, sulphur lupine, Wyeth eriogonum, and silky lupine.
DISTRIBUTION AND EXTENT: Northcentral Washington. The series is of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Colville Indian Reservation; Okanogan County, Washington, 1987.
SOURCE OF NAME: Achimin Basin in Okanogan County, Washington.
REMARKS: Diagnostic horizons and features recognized in this soil are a mollic epipedon from the surface to 18 inches, an argillic horizon from 18 to 34 inches, a clay increase of more than 20 percent (absolute) between A2 and Bt1 horizons, and a zone of secondary carbonate accumulation from 34 to 60 inches.