LOCATION SI WAEstablished Series
TAXONOMIC CLASS: Coarse-silty, mixed, superactive, nonacid, mesic Typic Udifluvents
TYPICAL PEDON: Si silt loam, pasture. (Colors are for moist soil unless otherwise stated.)
Ap--0 to 11 inches; dark brown (10YR 4/3) silt loam, pale brown (10YR 6/3) dry; strong medium and coarse granular structure; slightly hard, friable, slightly sticky, slightly plastic; many very fine and few fine roots; many very fine and few fine tubular pores; moderately acid (pH 5.6); abrupt smooth boundary. (6 to 11 inches thick)
Bw--11 to 22 inches; olive brown (2.5Y 4/4) silt loam, very pale brown (10YR 7/3) dry; weak, medium subangular blocky structure; soft, very friable, slightly sticky, slightly plastic; common fine and very fine roots; many very fine and many very fine irregular and common fine tubular pores; moderately acid (pH 5.6); abrupt smooth boundary. (10 to 20 inches thick)
C1--22 to 39 inches; light olive brown (2.5Y 5/4) stratified silt loam and fine sandy loamy light yellowish brown (2.5Y 6/4) and light gray (2.5Y 7/2) massive; soft, very friable, nonsticky, nonplastic; very few very fine roots; many very fine irregular and common fine tubular pores; moderately acid (pH 5.8); clear wavy boundary. (13 to 18 inches thick)
C2--39 to 60 inches; olive brown (2.5Y 4/4) and grayish brown (2.5Y 5/2) silt loam and fine sandy loam, light yellowish brown (2.5Y 6/4) and light gray (2.5Y 6/2) dry; massive; soft, very friable, nonsticky, nonplastic; very few very fine tubular; few roots; moderately acid (pH 5.6).
TYPE LOCATION: King County, Washington; 1,650 feet south, 2,540 feet east of the northwest corner of section 34, T.24N., R.8E.
RANGE IN CHARACTERISTICS: Soil temperature at 20 inches ranges from 47 to 52 degrees F. The difference between mean summer and mean winter soil temperature is 9 to 20 degrees F. These soils are usually moist. The control section contains 0 to 5 percent coarse fragments, 5 to 15 percent clay and less than 15 percent particles coarser than very fine sand by weighted average.
The Ap horizon has hue of 10YR or 2.5Y, value of 5 or 6 dry, and chroma of 2 or 3 moist and dry. Structure ranges from weak to moderate medium and fine granular.
The Bw horizon has hue of 10YR or 2.5Y, value of 4 or 5 moist, 5 to 7 dry, and chroma of 2 to 4 moist and dry.
The C horizon has hue of 2.5Y or 5Y, value of 4 or 5 moist, 6 or 7 dry, and chroma of 2 to 4 moist and dry. It is stratified silt loam to fine sandy loam and has some thin strata of loamy fine sand or fine sand in some pedons. Reaction is moderately acid or slightly acid.
COMPETING SERIES: These are the Arenzville, Chaseburg, Hadley, Haymond and Juneau. All of these soils have more than 20 degrees F difference between mean winter and mean summer soil temperature. In addition, Arenzville soils have a buried Ab horizon at a depth of 20 to 40 inches. Chaseburg, Hadley, and Haymond soils lack a Bw horizon. Juneau soils have a buried A or B horizon at depths of 20 to 40 inches.
GEOGRAPHIC SETTING: Si soils are on flood plains and low terraces at elevations ranging from 400 to 500 feet. They formed in recent alluvium. Average January temperature is 38 degrees F, an average July temperature is 63 degrees F, and mean annual temperature is 50 degrees F. The frost free season is near 150 days. The average annual precipitation is 70 to 80 inches, most of which falls as rain during the winter months. Each of the summer months has at least 1 inch of precipitation. Snow is infrequent.
GEOGRAPHICALLY ASSOCIATED SOILS: These include the Bellingham, Everett, Edgewick, Nooksack, Pilchuck, Puget, Salal, Seattle, and Tukwila soils. Bellingham soils are in a fine family. Edgewick soils are coarse-loamy and have an umbric epipedon. Everett soils are sandy-skeletal. Nooksack soils have a mollic epipedon. Pilchuck soils are sandy. Puget soils have an aquic moisture regime. Salal soils have an umbric epipedon. Seattle and Tukwila soils are Histosols.
DRAINAGE AND PERMEABILITY: Moderately well drained; runoff is medium; permeability is moderate. A water table is as high as 2 to 4 feet at times from November to April.
USE AND VEGETATION: Mostly used for cropland and pasture. Corn for silage, and grass-legume hay are common crops. Native vegetation is Douglas-fir, western redcedar, red alder, and black cottonwood with an understory of western swordfern, trailing blackberry, salmonberry, and thimbleberry.
DISTRIBUTION AND EXTENT: This series is inextensive and located in the Snoqualmie Valley near North Bend, King County, Washington.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: King County, Washington, 1971.
REMARKS: Diagnostic horizons and features recognized in this pedon are an ochric epipedon from the surface to 11 inches and a particle-size control section from 10 to 40 inches that has an assumed irregular decrease in organic carbon. The C horizon is assumed to have more than 0.2 percent organic carbon at 60 inches.