LOCATION SHILLA IDEstablished Series
TAXONOMIC CLASS: Ashy over loamy-skeletal, isotic, frigid Alfic Vitrixerands
TYPICAL PEDON: Shilla ashy silt loam -- on a 3 percent slope at 5,165 feet elevation in coniferous forest. When described on August 5, 1991 the soil was moist throughout. (Colors are for dry soil unless otherwise stated).
Oi--0 to 1 inch; slightly decomposed needles, moss, and twigs.
A--1 to 2 inches; dark grayish brown (10YR 4/2) ashy silt loam, very dark brown (10YR 2/2) moist; moderate fine granular structure; soft, very friable, nonsticky and nonplastic; many fine and very fine and few medium roots throughout; few very fine and fine tubular pores; slightly acid (pH 6.3); abrupt smooth boundary. (1 to 4 inches thick)
Bw1--2 to 10 inches; light yellowish brown (10YR 6/4) ashy silt loam, dark yellowish brown (10YR 4/4) moist; weak medium and coarse subangular blocky structure; soft, very friable, nonsticky and slightly plastic; common fine and very fine and few medium roots; common very fine tubular pores; 5 percent fine gravel; moderately acid (pH 6.0); gradual smooth boundary.
Bw2--10 to 17 inches; light yellowish brown (10YR 6/4) ashy silt loam, dark yellowish brown (10YR 4/4) moist; weak medium subangular blocky structure; soft, very friable, nonsticky and slightly plastic; common fine and very fine and few medium roots; common very fine tubular pores; 5 percent fine gravel; moderately acid (pH 5.9); abrupt irregular boundary. (combined thickness of the Bw1 and Bw2 horizons is 12 to 18 inches)
2Btb1--17 to 25 inches; yellowish brown (10YR 5/4) loam, dark yellowish brown (10YR 3/4) moist; moderate medium subangular blocky structure; slightly hard, friable, slightly sticky and moderately plastic; common fine and few medium roots; many fine and very fine tubular pores; many distinct discontinuous dark yellowish brown (10YR 4/6) clay films on faces of peds; 10 percent gravel; moderately acid (pH 5.9); clear wavy boundary. (2 to 12 inches thick)
2Btb2--25 to 32 inches; light yellowish brown (10YR 6/4) very gravelly clay loam, dark yellowish brown (10YR 3/4) moist; moderate fine subangular blocky structure; slightly hard, friable, slightly sticky and moderately plastic; common fine and few medium roots; many fine and very fine tubular pores; common distinct discontinuous dark yellowish brown (10YR 4/6) clay films on faces of peds; 45 percent gravel, 15 percent cobbles; moderately acid (pH 6.0); gradual wavy boundary.
2Btb3--32 to 54 inches; yellowish brown (10YR 5/6) extremely cobbly clay loam, dark yellowish brown (10YR 4/4) moist; moderate fine and very fine angular blocky structure; hard, friable, moderately sticky and moderately plastic; few fine roots matted around rock fragments; common fine and very fine tubular pores; few distinct discontinuous dark yellowish brown (10YR 4/6) clay films on faces of peds; 35 percent gravel, 55 percent cobbles; slightly acid (pH 6.2); clear irregular boundary. (combined thickness of the 2Btb2 and 2Btb3 horizons is 16 to 36 inches)
2R--54 inches; fractured basalt.
TYPE LOCATION: Nez Perce County, Idaho; about 3 miles north of Zaza, about 545 feet south and 2,600 feet east of the northwest corner of section 21, T. 32 N. R. 4 W.; USGS Frye Point topographic quadrangle; lat. 46 degrees, 06 minutes, 22 seconds N. and long. 116 degrees, 50 minutes, 17 seconds W.
RANGE IN CHARACTERISTICS:
Depth to bedrock - 40 to 60 inches
Average annual soil temperature - 43 to 45 degrees F
Volcanic ash mantle
Thickness - 14 to 20 inches
Volcanic glass content, 0.02 to 2mm fraction - 25 to 45 percent
Acid-oxalate extractable Al plus 1/2 Fe - 0.6 to 2.0 percent
Moist bulk density - .75 to .90 g/cc
15 bar water retention - 8 to 12 percent
Particle-size control section, lower part (weighted averages)
Clay content - 28 to 34 percent
Rock fragment content - 45 to 60 percent
A horizon
Value - 4 or 5 dry, 2 through 4 moist
Chroma - 2 or 3, dry or moist
Reaction - moderately acid or slightly acid
Bw horizon
Hue - 7.5YR or 10YR
Value - 5 or 6 dry, 3 or 4 moist
Gravel content - 0 to 10 percent, dominantly 2 to 5mm
Clay content - 10 to 15 percent (field estimate)
Reaction - slightly acid or moderately acid
2Btb horizon, upper part
Texture - L, CB-L, CL, CB-CL
Rock fragment content - 10 to 25 percent
Clay content - 24 to 30 percent
Reaction - moderately acid or slightly acid
2Btb horizon, lower part
Hue - 7.5YR or 10YR
Value - 5 or 6 dry, 3 or 4 moist
Chroma - 4 through 6, dry or moist
Textures - CBV-CL, CBX-CL, GRV-CL, GRX-CL
Rock fragment content - 40 to 90 percent
Clay content - 28 to 38 percent
Reaction - moderately acid or slightly acid
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING: Shilla soils are on hillsides and summits on basalt plateaus at elevations of 4,400 to 5,300 feet. Slopes range from 2 to 30 percent. These soils formed in volcanic ash over material weathered from basalt. Average annual precipitation is 26 to 28 inches, average annual temperature is 41 to 43 degrees F., and the frost free period is 60 to 70 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Larabee and Webbridge soils. Larabee soils are moderately deep, do not contain andic material, and are on south- and west-facing hillsides. Webbridge soils are cryic and udic, do not have an argillic horizon, and are on steep north- and east-facing slopes.
DRAINAGE AND PERMEABILITY: Well drained; slow to rapid runoff; moderately slow permeability.
USE AND VEGETATION: These soils are used for timber production and livestock grazing. Native vegetation is mainly grand fir, Douglas-fir, common snowberry, longtube twinflower, and goldthread.
DISTRIBUTION AND EXTENT: This soil is of small extent in northern Idaho.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Nez Perce County, Idaho, 1992.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - from the surface to 7 inches mixed (Oi, A, and part of the Bw1 horizons).
Andic materials - from 1 to 17 inches (A, Bw1, and Bw2 horizons)
Argillic horizon - from 17 to 54 inches (2Btb1, 2Btb2, and 2Btb3 horizons).
Particle-size control section - the zone from the mineral surface to 40 inches (A, Bw1, Bw2, 2Btb1, and 2Btb2 horizons, and part of the 2Btb3 horizon).
ADDITIONAL DATA: This pedon was sampled for analysis at the NSSL. Laboratory sample number 91P1096, soil survey sample number S91ID-069-031.