LOCATION ALPOWA WA+IDEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, mesic Calcic Haploxerolls
TYPICAL PEDON: Alpowa cobbly silt loam, pasture. (Colors are for dry soil unless otherwise noted.)
A1--0 to 7 inches; grayish brown (10YR 5/2) cobbly silt loam, very dark brown (10YR 2/2) moist; weak fine granular structure; slightly hard, friable, slightly sticky and slightly plastic; many fine roots; 30 percent basalt cobbles and pebbles; slightly alkaline (pH 7.8); clear wavy boundary. (5 to 14 inches thick)
A2--7 to 15 inches; brown (10YR 5/3) gravelly silt loam, dark brown (10YR 3/3) moist; massive; slightly hard, friable, slightly sticky and slightly plastic; many fine roots; 35 percent pebbles and cobbles; moderately alkaline (pH 8.0); clear wavy boundary. (2 to 10 inches thick)
Bk1--15 to 31 inches; pale brown (10YR 6/3) very gravelly silt loam, dark brown (10YR 4/3) moist; massive; slightly hard, friable, slightly sticky and slightly plastic; common fine roots; many very fine pores; many coatings of lime on undersides of rock fragments; 40 percent pebbles and cobbles; violent effervescence; moderately alkaline (pH 8.2); gradual wavy boundary. (12 to 20 inches thick)
Bk2--31 to 49 inches; very pale brown (10YR 7/3) very gravelly loam, brown (10YR 5/3) moist; massive; slightly hard, friable, slightly sticky and slightly plastic; common fine roots; many very fine pores; 45 percent pebbles and cobbles; violent effervescence; strongly alkaline (pH 8.5); gradual wavy boundary. (14 to 22 inches thick)
2Bk3--49 to 60 inches; light yellowish brown (10YR 6/4) very gravelly coarse sandy loam, dark yellowish brown (10YR 4/4) moist; massive; soft, very friable, nonsticky and nonplastic; common fine roots; 45 percent pebbles and cobbles; continuous coatings of lime on undersides of rock fragments; violent effervescence; strongly alkaline (pH 9.0).
TYPE LOCATION: Garfield County, Washington; 600 feet east and 620 feet south of the northwest corner of sec. 20, T. 11 N., R. 44 E.
RANGE IN CHARACTERISTICS: The mollic epipedon is 7 to 15 inches thick. The mean annual soil temperature at depth of 20 inches is 49 to 52 degrees F. These soils are usually moist, but are dry in all parts between depths of 8 and 24 inches for 90 to 105 consecutive days. The 10- and 40-inch control section averages less than 18 percent clay and 35 to 50 percent rock fragments. Depth to carbonates is 12 to 30 inches.
The A horizon has value of 4 or 5 dry, 2 or 3 moist, and chroma of 2 or 3 dry or moist. It has weak granular or blocky structure and is mildly or moderately alkaline.
The Bw horizon, where present, has value of 5 or 6 dry, and 3 or 4 moist. It is mildly alkaline or moderately alkaline. It is very gravelly silt loam, very cobbly silt loam, very gravelly loam or very cobbly loam.
The Bk horizon has value of 5 through 7 dry, 3 through 5 moist, and chroma of 1 through 4 dry or moist. It is silt loam or loam and is very gravelly or very cobbly to depths of 40 inches and ranges to very cobbly or very gravelly coarse sandy loam below 40 inches. It is slightly alkaline to strongly alkaline.
COMPETING SERIES: These are the Bonnet, Copperton, Hupp, Lakewin, Middle, Schuelke, and Stember series. Bonnet soils have a mean annual soil temperature of 54 to 59 degrees F. Copperton soils have a weakly to moderately cemented horizon at a depth of 12 to 30 inches. Hupp soils are 18 to 24 percent clay in the particle-size control section. Lakewin soils have a very gravelly sand 2C horizon beginning at 17 to 27 inches. Middle, Schuelke, and Stember soils have a lithic contact at 20 to 40 inches.
GEOGRAPHIC SETTING: Alpowa soils are on on lower canyon walls, hills and plateaus at elevations of 600 to 3,000 feet in Washington and northern Idaho, and alluvial fans at elevations of 4,300 to 5.800 feet in Idaho. Slopes are 1 to 75 percent. Alpowa soils formed in slope alluvium, colluvium, and alluvium from basalt and loess. Summers are warm and dry and winters are cool and moist. The average annual precipitation is 12 to 16 inches. The average July temperature is 69 to 72 degrees F. The average January temperature is 29 to 32 degrees F. The mean annual temperature is 48 to 52 degrees F. The frost-free season is 135 to 180 days in Washington and northern Idaho and 100 to 135 days in Idaho.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Anders, Bedke, Bolicker, Chard, Lickskillet, Nansene, Schuelke, Walla Walla, and Weeks soils. Anders and Schuelke soils have lithic contact at depths of 20 to 40 inches. Bolicker and Chard soils are coarse-loamy. Lickskillet soils have lithic contact at depths of 10 to 20 inches. Nansene and Walla Walla soils are coarse-silty and lack secondary lime above depth of 43 inches. Bedke soils have a fine-loamy Bt horizon and an aridic moisture regime. Weeks soils are coarse-loamy and have a duripan.
DRAINAGE AND PERMEABILITY: Well drained; slow to rapid runoff; moderate permeability.
USE AND VEGETATION: Largely under native grasses used for range, wildlife, recreation, and watershed protection. Vegetation is mainly bluebunch wheatgrass, Idaho fescue, Sandberg bluegrass, and rabbitbrush.
DISTRIBUTION AND EXTENT: Southeastern Washington and southern Idaho. Series is moderately extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Garfield County (Garfield County Area), Washington, 1970.
REMARKS: Diagnostic horizons and features recognized in this pedon are a mollic epipedon from the surface to 15 inches and a zone of calcium carbonate accumulation from 15 to 60 inches.