LOCATION OMAK WAEstablished Series
TAXONOMIC CLASS: Fine, isotic, mesic Vitrandic Durixerolls
TYPICAL PEDON: Omak ashy silt loam on a 2 percent northwest-facing slope at an elevation of 2,350 feet, under a ponderosa pine canopy. (Colors are for air-dry soil unless otherwise stated.)
Oi--0 to 2 inches; fresh and partially decayed ponderosa pine needles, twigs, and cones; abrupt smooth boundary.
A1--2 to 7 inches; brown (10YR 5/3) ashy silt loam, dark brown (10YR 3/3) moist; weak very fine subangular blocky structure; slightly hard, very friable, slightly sticky and nonplastic; common very fine and fine roots; neutral (pH 7.0); clear smooth boundary.
A2--7 to 12 inches; brown (10YR 5/3) ashy silt loam, dark brown (10YR 3/3) moist; weak fine subangular blocky structure; slightly hard, very friable, slightly sticky and slightly plastic; common fine and few medium roots; neutral (pH 6.8); clear smooth boundary. (Combined thickness of the A horizon is 10 to 14 inches).
E--12 to 17 inches; pale brown (10YR 6/3) silt loam, brown (10YR 5/3) moist; weak fine subangular blocky structure; hard, firm, slightly sticky and slightly plastic; common fine and medium roots, few coarse roots; 2 percent pebbles; neutral (pH 6.8); abrupt smooth boundary. (0 to 6 inches thick)
Bt/E--17 to 28 inches; 60 percent light brownish gray (2.5Y 6/2) silt loam (Bt part), olive brown (2.5Y 4/4) moist; 40 percent light gray (2.5Y 7/2) heavy silt loam (E part), light brownish gray (2.5Y 6/2) moist; moderate fine angular blocky structure; hard, firm, slightly sticky and slightly plastic; few fine roots; few faint clay films on faces of peds (B part); neutral (pH 7.0); abrupt smooth boundary. (4 to 12 inches thick)
Bt--28 to 40 inches; light yellowish brown (2.5Y 6/4) silty clay loam, olive brown (2.5Y 4/4) moist; moderate fine angular blocky structure; hard, firm, moderately sticky and moderately plastic; few fine roots; common distinct clay films on faces of peds; neutral (pH 7.2); clear smooth boundary. (6 to 13 inches thick)
Bqm--40 to 47 inches; light yellowish brown (2.5Y 6/4) silica-cemented duripan which crushes to sandy loam, olive brown (2.5Y 4/4) moist; massive; very hard, very firm, slightly sticky and nonplastic; strongly cemented; mat of very fine and fine roots at top of duripan; 5 percent pebbles; moderately alkaline (pH 8.2) abrupt wavy boundary. (1 to 9 inches thick)
Bkqm--47 inches; light gray (2.5Y 7/2) silica-cemented duripan which crushes to sandy loam, olive brown (2.5Y 4/4) moist; massive; extremely hard, very firm; nonsticky and nonplastic; indurated; 5 percent pebbles; strongly alkaline (pH 8.6); weakly effervescent; few masses of segregated lime.
TYPE LOCATION: Colville Indian Reservation; Okanogan County, Washington; about 11 miles east of the city of Omak; 1,500 feet west, 1,100 feet north of the southeast corner of sec. 21, T. 33 N., R. 28 E., W.M.
RANGE IN CHARACTERISTICS: The mean annual soil temperature at a depth of 20 inches is 47 to 50 degrees F. These soils are usually moist but are dry in all parts between depths of 4 and 12 inches for 75 to 90 consecutive days following the summer solstice. The mollic epipedon is 7 to 14 inches thick. The upper 7 to 14 inches has an estimated moist bulk density of 1.35 to 1.45 g/cc, volcanic glass content of 5 to 20 percent, acid-oxalate extractable aluminum plus one-half of the acid-oxalate extractable iron of 0.4 to 1.0 percent, and 15-bar water retention of 5 to 10 percent for air dried samples. Depth to the silica-cemented duripan ranges from 20 to 40 inches. The particle-size control section averages 35 to 45 percent clay.
The A horizon has value of 4 or 5 dry, and chroma of 1 through 3 dry or moist. It is 0 to 10 percent pebbles. Reaction is slightly acid or neutral.
The E horizon has a hue of 10YR or 2.5Y, value of 6 or 7 dry, 4 or 5 moist, and chroma of 2 through 4 moist or dry. It is loam or silt loam and is 0 to 10 percent pebbles. Reaction is slightly acid or neutral.
The Bt part of the Bt/E horizon has hue of 10YR or 2.5Y, value of 6 or 7 dry, 4 or 5 moist, and chroma of 2 through 4 moist or dry. The E part has hue of 10YR or 2.5Y, values of 6 through 8 dry, 5 or 6 moist, and chromas of 1 through 3 moist or dry. Both are 0 to 10 percent pebbles. Both are slightly acid or neutral.
The Bt horizon has hue of 2.5Y or 10YR , value of 5 through 7 dry, 4 through 7 moist, and chroma of 2 through 4 moist or dry. It is clay loam, silty clay loam, or silty clay. It is 0 to 10 percent pebbles and 0 to 5 percent cobbles.
The Bqm horizon has hue of 2.5Y or 10YR, value of 5 through 7 dry, 4 through 7 moist, and chroma of 2 through 4 moist or dry. It is stratified and crushes to sandy loam, fine sandy loam, loam or silt loam. It is 0 to 10 percent pebbles and 0 to 5 percent cobbles. Reaction is slightly alkaline or moderately alkaline.
The Bkqm horizon has hue of 10YR or 2.5Y; value of 6 or 7 dry,4 or 5 moist, and chroma of 2 through 4 dry or moist. It crushes to sandy loam or fine sandy loam. It is 0 to 10 percent pebbles. Reaction ranges from moderately alkaline to very strongly alkaline.
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING: Omak soils are on glaciolacustrine influenced moraine and terraces. Slopes are 0 to 15 percent. These soils formed in intermixed glaciolacustrine sediments and glacial till with a component of loess and volcanic ash in the upper part. Elevations range from 2,100 to 3,000 feet. The climate is characterized by warm, dry summers and cool, moist winters. The average annual precipitation is 15 to 20 inches. The mean January temperature is about 24 degrees F, mean July temperature is about 67 degrees F, and the mean annual air temperature is about 47 degrees F. The frost-free season is 100 to 130 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Bernhill, Cedonia, Donavan, Hunters, and Martella soils. Bernhill, Cedonia, Donavan, and Hunters soils are well drained and very deep. Martella soils have a volcanic ash mantle 7 to 14 inches thick, lack a duripan, and are frigid.
DRAINAGE AND PERMEABILITY: Moderately well drained, slow runoff; moderately slow permeability above the duripan and very slow through the duripan.
USE AND VEGETATION: Principal uses are timber production, livestock grazing, watershed, wildlife habitat, nonirrigated cultivated crops with wheat as the principal crop, and hay and pasture. The native vegetation is ponderosa pine with an understory of common snowberry, Idaho fescue, bluebunch wheatgrass, rose, heartleaf arnica, and groundsel.
DISTRIBUTION AND EXTENT: Northcentral Washington. This series is of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Colville Indian Reservation; Okanogan County, Washington, 1987.
REMARKS: Diagnostic horizons and features recognized in this soil are a mollic epipedon from the mineral surface to 12 inches, an argillic horizon from 28 to 40 inches, and a duripan at 40 inches. The description reflects a change in classification from fine, mixed, mesic Vitrandic Durixerolls to fine, isotic, mesic Vitrandic Durixerolls.