LOCATION SEMIAHMOO WA+OR

Established Series
Rev. AD/MPR/SBC
07/2014

SEMIAHMOO SERIES

The Semiahmoo series consists of very deep, very poorly drained soils formed in herbaceous organic deposits. Semiahmoo soils are in depressions on glacial outwash plains and broad flood plains. Slopes are 0 to 3 percent. The mean annual precipitation is about 50 inches and the mean annual temperature is about 48 degrees F.

TAXONOMIC CLASS: Euic, mesic Typic Haplosaprists

TYPICAL PEDON: Semiahmoo muck - abandoned cropland. (Colors are for moist soil unless otherwise noted.)

Oap--0 to 15 centimeters; black (5YR 2/1) muck (sapric material), dark gray (10YR 4/1) dry; moderate fine granular structure; slightly hard, very friable, slightly sticky and slightly plastic; l2 percent fiber, 3 percent rubbed; many very fine and fine roots; many very fine pores; strongly acid (pH 5.2); clear smooth boundary.

Oa1--15 to 30 centimeters; black (5YR 2/1) muck (sapric material), dark gray (10YR 4/1) dry; strong medium subangular blocky structure; slightly hard, very friable, slightly sticky and slightly plastic; l2 percent fiber, 3 percent rubbed; many very fine and fine roots; few very fine pores; strongly acid (pH 5.2); abrupt smooth boundary.

Oa2--30 to 56 centimeters; dark reddish brown (5YR 2/2) muck (sapric material), dark grayish brown (10YR 4/2) dry; very thin platy structure; 60 percent fiber, l2 percent rubbed; common very fine and fine roots; few fine pores; strongly acid (pH 5.2); abrupt smooth boundary.

Oa3--56 to 89 centimeters; black (5YR 2/1) muck (sapric material), dark gray (10YR 4/1) dry; very thin platy structure; hard, very friable, nonsticky and slightly plastic; 40 percent fiber, l0 percent rubbed; few fine roots; few fine pores; strongly acid (pH 5.1); abrupt smooth boundary.

Oa4--89 to 135 centimeters; very dark brown (10YR 2/2) muck (sapric material), dark grayish brown (10YR 4/2) dry; massive; hard, very friable, nonsticky and slightly plastic; 60 percent fiber, l2 percent rubbed; few fine roots; few fine pores; very strongly acid (pH 5.0); abrupt smooth boundary. (combined thickness of the Oa horizons is 130 to 215 centimeters)

2Cg--135 to 155 centimeters; dark grayish brown (10YR 4/2) silty clay, light brownish gray (10YR 6/2) dry; massive; very hard, firm, sticky and plastic; few herbaceous and woody fibers; very strongly acid (pH 5.0); abrupt smooth boundary. (0 to many feet thick)

30e--155 to 165 centimeters; dark reddish brown (5YR 2/2) on broken face and rubbed; mucky peat (hemic material), massive; hard, very friable, nonsticky and slightly plastic; 70 percent fiber, 20 percent rubbed; slightly acid (pH 6.4).

TYPE LOCATION: Pierce County, Washington; 61 meters west and 686 meters north of southeast corner of section. l4, T. 20 N., R. 4 E.

RANGE IN CHARACTERISTICS:

Mean annual soil temperature - 8 to 12 degrees C.
Depth to mineral soil - greater than 130 centimeters

Oa horizons
Hue - 2.5YR to 10YR
Value - 2 to 3 moist, 2 to 4 dry
Chroma - 1 to 3 moist or dry
Fiber content - 20 to 60 percent unrubbed and 3 to 13 percent rubbed
Reaction - very strongly acid to moderately acid

2Cg horizon
Value - 4 or 5 moist, 5 or 6 dry
Chroma - 1 or 2 moist and dry
Texture - S, LS, SL, L, SIL, SICL, or SIC
Reaction - very strongly acid to moderately acid

3Oe horizon
Hue - 5YR to 10YR
Value - 2 to 3 moist, 3 or 4 dry
Chroma - 1 to 3 moist or dry
Fiber content - 60 to 80 percent unrubbed and 17 to 50 percent rubbed
Reaction - slightly acid or moderately acid

COMPETING SERIES: These are the Carlisle, Catden, Houghton, Lena, Peteetneet, and Saltese series. Carlisle soils have 15 to 30 percent woody fragments in the control section. Catden soils have woody fibers, unrubbed in the subsurface tier. Houghton and Peteetneet soils are slightly acid or neutral. Lena soils are calcareous throughout. Saltese soils have a mean July temperature of about 19 to 22 degrees C. and a mean January temperature of about 4 to -1 degrees C.

GEOGRAPHIC SETTING: Semiahmoo soils are in depressions on glacial outwash plains and broad floodplains at elevations ranging from near sea level to about 395 meters. They formed in herbaceous organic deposits. The climate is characterized by warm dry summers and mild moist winters. The mean annual precipitation is 889 to 1778 millimeters. The mean January temperature is about 1 degrees C., mean July temperature is about 17 degrees C., and the mean annual temperature is about 9 degrees C. The frost-free season is l25 to 250 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Shalcar, Snohomish, and Sultan soils. Shalcar soils have a loamy substratum at depth of less than 130 centimeters. Snohomish soils are mineral soil over buried organic soil materials. Sultan soils are mineral soils.

DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY: Very poorly drained; moderately high saturated hydraulic conductivity. Depth to seasonal high water table ranges from 30 centimeters above the surface to the soil surface to the November through May.

USE AND VEGETATION: Semiahmoo soils are used for wildlife habitat, livestock grazing, forage crop production, and crop production consisting of truck crops and berries. Potential natural vegetation consists of willows, sedges, cattails, skunkcabbage, redosier dogwood, spirea, and reeds.

DISTRIBUTION AND EXTENT: This series is of moderate extent in the Puget Sound Basin of Western Washington and Northern Willamette Valley in Western Oregon.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon

SERIES ESTABLISHED: Whatcom County, Washington, l945.

REMARKS:
The original series description in Whatcom County was correlated to the Pangborn series which are Dysic, mesic Typic Haplosaprists

ADDITIONAL DATA: NSSL pedons 00P1324 and 00P1326

National Cooperative Soil Survey
U.S.A.