Established Series


Typically, Sammamish soils have very dark grayish brown silt loam A horizons and stratified grayish brown and gray loamy and sandy B horizons.

TAXONOMIC CLASS: Fine-loamy, mixed, superactive, nonacid, mesic Fluvaquentic Humaquepts

TYPICAL PEDON: Sammamish silt loam, pasture. (Colors are for moist soil unless otherwise noted.)

Ap--0 to 12 inches; very dark grayish brown (10YR 3/2) silt loam, grayish brown (10YR 5/2) dry; moderate medium crumb structure; slightly hard, very friable; many roots; many very fine pores; strongly acid (pH 5.4); abrupt smooth boundary. (10 to 12 inches thick)

B21--12 to 30 inches; dark grayish brown (2.5Y 4/2) silt loam and loamy sand, light brownish gray (2.5Y 6/2) dry; many medium prominent brown (7.5YR 4/4) strong brown (7.5YR 5/6) and dark brown (7.5YR 3/2) mottles; massive; slightly hard, friable; common roots; many very fine pores; neutral (pH 6.6); clear smooth boundary. (16 to 20 inches thick)

B22--30 to 48 inches; olive gray (5Y 4/2) fine sandy loam and silt loam, grayish brown (2.5Y 5/2) dry; fine prominent yellowish red (5YR 4/8) mottles; massive; slightly hard, very friable; few roots; many very fine pores; slightly acid (pH 6.4).

TYPE LOCATION: King County, Washington; 350 feet north, 50 feet east of center section 21, T.24N., R.6E.

RANGE IN CHARACTERISTICS: The solum is more than 40 inches thick. The mean annual soil temperature is about 50 degrees F. These soils are usually moist. The series control section averages 8 to 25 percent clay, more than 15 percent fine and coarser sand, and less than 5 percent coarse fragments.

The Ap horizon is slightly acid to strongly acid. It has less than 50 percent base saturation.

Th B horizon is dark grayish brown (2.5Y 4/2), olive gray (5Y 4/2), and grayish brown (2.5Y 5/2) and contains many strong brown (7.5YR 5/6), brown (7.5YR 4/4), dark brown (7.5YR 3/2), and yellowish red (5YR 4/8) mottles. It is stratified silt loam, loam, or fine sandy loam and contains lenses of loamy sand or sandy clay loam. This horizon is slightly acid or neutral.

COMPETING SERIES: These are the Bellingham, Nestucca, Norma, and Samish series. Bellingham and Nestucca soils contain less than 15 percent fine and coarser sand. Norma soils average less than 18 percent clay in the series control section. Samish soils have ochric epipedons.

GEOGRAPHIC SETTING: These soils are on nearly level to gently sloping topography at elevations up to 50 feet above sea level. They formed in alluvium or glacial outwash. They are in a humid climate. The average January temperature is 38 degrees F.; the average July temperature is 64 degrees F.; and the mean annual temperature is near 50 degrees F. The frost free season is near 200 days. The mean annual precipitation is about 50 inches, most of which falls as rain during winter but each month of summer receives at least 1 inch of rainfall. Snow is infrequent.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Bellingham soils, and the Puget and Sultan soils. Puget soils have ochric epipedons and are dominantly silty clay loam in the B horizon. Sultan soils have ochric epipedons.

DRAINAGE AND PERMEABILITY: Somewhat poorly drained; slow runoff; moderate to moderately slow permeability.

USE AND VEGETATION: Sammamish soils are used mostly for seeded grass pasture.

DISTRIBUTION AND EXTENT: This series is inextensive. The soils occur in stream valleys and local glacial lake depressions in Puget Sound Basin, Washington.


SERIES ESTABLISHED: King County, Washington, 1943.

REMARKS: The Sammamish soils would have been considered as Humic Gley (Wiesenboden) soils in the modified 1938 yearbook classification system.

National Cooperative Soil Survey