LOCATION SNOHOMISH WAEstablished Series
TAXONOMIC CLASS: Fine-silty, mixed, superactive, nonacid, mesic Thapto-Histic Fluvaquents
TYPICAL PEDON: Snohomish silt loam - cultivated and drained. (Colors are for moist soil unless otherwise noted.)
Apl--0 to 7 inches; very dark grayish brown (10YR 3/2) silt loam, light brownish gray (10YR 6/2) dry; moderate fine and medium granular structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine and few fine and medium roots; few very fine irregular pores; moderately acid (pH 6.0); abrupt smooth boundary. (5 to 10 inches thick)
Ap2--7 to 13 inches; very dark grayish brown (10YR 3/2) silt loam, light brownish gray (10YR 6/2) dry; few very fine distinct gray (5Y 5/1) mottles and few very fine faint strong brown (7.5YR 5/8) mottles; moderate medium and coarse subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine and few medium roots; few very fine irregular pores; slightly acid (pH 6.2); clear smooth boundary. (0 to 7 inches thick)
Cg1--13 to 23 inches; gray (5Y 5/1) silt loam, light gray (N 7/0) dry; common fine light olive gray (5Y 6/2) mottles and common medium yellowish brown (10YR 5/6, 5/8) mottles; massive; hard friable, sticky and plastic; few very fine roots; common very fine and few medium and coarse tubular pores; moderately acid (pH 6.0); abrupt smooth boundary. (4 to 18 inches thick)
Cg2--23 to 30 inches; gray (2.5Y 5/0) silt loam, light gray (2.5Y 7/0) dry; common fine faint gray (5Y 5/1) mottles and common medium distinct yellowish brown (10YR 5/8) mottles; massive; slightly hard, friable, slightly sticky and slightly plastic; few thin (1 to 2 mm) strata of hemic material; few very fine roots; few fine tubular pores; moderately acid (pH 5.8); clear smooth boundary. (0 to 7 inches thick)
Oa1--30 to 38 inches; dark grayish brown (2.5Y 4/2) and strong brown (7.5YR 5/8), brown (7.5YR 4/2) dry; 20 percent fibers, 5 percent rubbed; massive; hard, friable, slightly sticky, slightly plastic; contains 5 percent large roots and sticks and 10 percent strata of silt loam; moderately acid (pH 6.0); clear smooth boundary. (3 to 20 inches thick)
Oe--38 to 50 inches; very dark grayish brown (2.5Y 3/2) material, very dark gray (10YR 3/1) dry; massive; hard, friable, nonsticky, nonplastic; 60 percent fibers, 20 percent rubbed; massive; moderately acid (pH 6.0); clear smooth boundary. (0 to 20 inches thick)
Oa2--50 to 60 inches; black (2.5Y 2/2), very dark gray (10YR 3/1) dry; massive; hard, friable, slightly plastic, slightly sticky; 20 percent fibers, 1 percent rubbed; massive; moderately acid (pH 6.0); abrupt smooth boundary.
TYPE LOCATION: Skagit County, Washington; about 2 miles west of Burlington; 1,550 feet east and 150 feet north of the southwest corner of sec. 26, T. 35 N., R. 3 E.
RANGE IN CHARACTERISTICS: The average annual soil temperature is estimated to range from 49 to 52 degrees F. The upper part of the particle-size control section lacks coarse fragments, averages less than 15 percent fine and coarser sand, and averages 18 to 35 percent clay, and l5 to 60 percent volcanic ash. Depth to the organic layers ranges from 14 to 36 inches. These soils have an irregular distribution of organic matter with depth. Fibers in the lower part of the particle-size control section are mostly from grasses and sedges, but pedons average up to 15 percent wood fragments.
The A horizon has hue of 10YR or 2.5Y, value of 3 or 4 moist, 5 through 7 dry, and chroma of 1 through 3 moist and dry. Reaction is strongly acid to slightly acid. It is silt loam or silty clay loam.
The Cg horizon has hue of 10YR, 2.5Y, or 5Y, value of 3 through 6 moist, 5 through 8 dry, and chroma of 0 through 2 moist and dry. Reaction is strongly acid to slightly acid. It is silt loam, silty clay loam, or mucky silt loam.
The O horizons have hue of 2.5YR through 2.5Y, value 1 through 4 moist, 1 through 5 dry, and chroma of 0 through 4 moist and dry. Individual layers are sapric material or hemic material or stratified woody mucky peat, muck, sedge mucky peat, and sedimentary peat. The fiber content ranges from 20 to 80 percent unrubbed and 1 to 25 percent rubbed. Thin discontinuous layers of volcanic ash and diatomaceous earth (1/2 to 2 inches thick) occur between 24 and 48 inches in some pedons. Reaction is strongly acid or moderately acid. Some pedons have a mineral C horizon below 40 inches.
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING: The Snohomish soils are on flood plains and backswamps of flood plains at elevations of 5 to 300 feet. Slopes are 0 to 2 percent. They formed in alluvium with a component of volcanic ash underlain by organic materials. These soils are in a mild marine climate. Average annual precipitation is 22 to 50 inches. The average January temperature is about 38 degrees F; average July temperature is about 64 degrees F; and the average annual temperature is 48 to 52 degrees F. The frost-free season is 160 to 220 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the McMurry, Mukilteo, Puget, Semiahmoo, Skagit, and Sumas series. McMurry, Mukilteo, and Semiahmoo are organic soils. Puget, Skagit, and Sumas soils lack organic layers in the particle-size control section.
DRAINAGE AND PERMEABILITY: Poorly drained; slow to ponded runoff; moderately slow permeability to the underlying organic material and moderate through it. These soils are subject to occasional, brief periods of flooding from November through April. An apparent water table is as high as 0 to 1 foot from November through May unless drained.
USE AND VEGETATION: Most Snohomish soils are drained and used for cropland, hay, and pasture. The native vegetation was red alder, western redcedar, western hemlock, and sitka spruce with an understory of sedges, vine maple, salmonberry, redosier dogwood, Douglas spirea, sweetscented bedstraw, devilsclub, ladyfern, red elderberry, red huckleberry, western swordfern, skunkcabbage, salmonberry, and Douglas spirea.
DISTRIBUTION AND EXTENT: Puget lowlands in western Washington. Series is of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Snohomish County, Washington, 1938.
REMARKS: Partial laboratory data are available on these soils. Laboratory numbers S74-WA4-346-352. Diagnostic horizons and features recognized in this pedon are an ochric epipedon from the surface to 13 inches, an irregular decrease in organic carbon with depth and a lithologic change from alluvium to organic deposits at 30 inches.