LOCATION GWIN WA+ID OREstablished Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, mesic Lithic Argixerolls
TYPICAL PEDON: Gwin cobbly silt loam, rangeland (Colors are for dry soil unless otherwise noted)
A--0 to 5 inches; dark grayish brown (10YR 4/2) cobbly silt loam, very dark brown (10YR 2/2) moist; moderate to strong granular and weak thin platy structure; slightly hard, friable, slightly sticky and slightly plastic; many roots; 20 percent angular rock fragments; neutral (pH 6.6); clear smooth boundary. (2 to 8 inches thick)
Bt1--5 to 12 inches; dark grayish brown (10YR 4/2) very cobbly silty clay loam, very dark brown (10YR 2/2) moist; moderate coarse prismatic and moderate coarse subangular blocky structure; hard, firm, moderately sticky and moderately plastic; many roots; many fine continuous tubular pores; few faint clay films on vertical and horizontal faces of peds; 55 percent angular rock fragments; neutral (pH 6.6); gradual wavy boundary. (4 to 9 inches thick)
Bt2--12 to 17 inches; brown (7.5YR 4/2) extremely cobbly silty clay loam, dark brown (7.5YR 3/2) moist; moderate medium subangular blocky structure; hard, firm, moderately sticky and moderately plastic; few roots; few faint black (10YR 2/1) clay films on faces of peds and rock fragments; 60 percent angular rock fragments; neutral (pH 6.6); gradual wavy boundary. (0 to 12 inches thick)
R--17 inches; basalt
TYPE LOCATION: Walla Walla County, Washington; on Black Snake Ridge; SW1/4SW1/4 section 3, T. 7 N., R. 38 E.
RANGE IN CHARACTERISTICS: Mean annual soil temperature is about 47 to 54 degrees F. These soils are usually moist, but are dry in the moisture control section for 60 to 75 consecutive days following summer solstice but range to 45 days in western Idaho (xeric moisture regime). The solum thickness and depth to bedrock range from 10 to 20 inches. The particle-size control section contains 40 to 90 percent gravel, cobbles, and stones, and 15 to 35 percent clay. The soils are slightly acid to slightly alkaline. Hue is 10YR or 7.5YR throughout.
The A horizon has value of 3 through 5 dry. 2 or 3 moist, through and chroma of 1 through 6 dry, 1 through 3 moist, through. It has weak to strong structure.
The BA horizon, when present, has colors similar to the A horizon, but has textures and rock fragments similar to the Bt horizon.
The Bt horizon has value of 3 through 6 dry, 2 through 4 moist, through, and chroma of 1 through 6 dry, and 1 through 4 moist.. It is heavy silt loam, loam, clay loam or silty clay loam and has 35 to 90 percent rock fragments.
COMPETING SERIES: These are the Argabak, Bellehelen, Brier, Canfire, Chinabutte, Clovercreek, Duco, Horseflat, Nuhelen, Ocud (T), Orhood, Reywat, Shepridge, Stepmount, Upatad and Windry series. Argabak, Bellehelen, Brier, Duco, Horseflat, Nuhelen, Ocud, Orhood, Reywat and Upatad soils are usually dry and have aridic soil moisture regimes. In addition, Argabak soils are very shallow, and Upatad soils have Btq and Btkq horizons. Canfire and Chinabutte soils are dry for 75 to 90 consecutive days. Clovercreek soils contain mainly gravel of greenstone origin. Nuhelen soils are 7 to 14 inches to welded tuff and have sandy loam and sandy clay loam textures. Shepridge soils formed in colluvium or alluvium over residuum from quartzite and the moisture regime is xeric bordering on aridic. Stepmount soils have secondary carbonates at a depth of 9 to 18 inches and Btk horizons. Windry soils are dry 90 to 100 consecutive days.
GEOGRAPHIC SETTING: These soils are on mountain slopes, basalt plateaus, ridgetops, foothills, structural benches, hill shoulders, summits, backslopes, and footslopes and canyon walls. They formed in colluvium and residuum from basalt mixed with loess. Slopes are 0 to 90 percent. Elevations range from 1,600 to 4,500 feet in Washington, and from 800 to 6,210 feet in Oregon and Idaho. Highest elevations are on south aspects only. The climate can be characterized by cool, wet winters and hot, dry summers. Mean annual precipitation ranges from 14 to 24 inches in Washington, 14 to 33 inches in Idaho, and 14 to 28 inches in Oregon. Mean January temperature is 25 to 29 degrees F; mean July temperature is 66 to 72 degrees F; and mean annual temperature is 43 to 52 degrees F. Frost-free season is 90 to 180 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Athena, Balder, Couse, Klicker, Palouse, and Rockly soils. Athena, Couse, Klicker, and Palouse soils are deeper than 20 inches to bedrock. Balder soils lack an argillic horizon and are 10 to 20 inches deep to paralithic contact. Rockly soils lack an argillic horizon and are 4 to 12 inches deep to bedrock.
DRAINAGE AND PERMEABILITY: Well drained, slow to very rapid runoff, moderately slow permeability.
USE AND VEGETATION: The Gwin soil is used for grazing and as wildlife habitat. Native vegetation is mainly bluebunch wheatgrass, Idaho fescue, and Sandberg bluegrass.
DISTRIBUTION AND EXTENT: Gwin soils are in eastern and central Washington, eastern Oregon, and western Idaho. MLRA 8, 9, and 10. Gwin soils are extensive.
MLRA OFFICE RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Walla Walla County, Washington, 1960.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - from the surface to 17 inches (A, Bt1 and Bt2 horizons)
Argillic horizon - from 5 to 17 inches (Bt1 and Bt2 horizon)
Lithic contact - at 17 inches (R horizon)
Particle-size control section - from 5 to 17 inches (Bt1 and Bt2 horizons)
Xeric moisture regime