LOCATION TACOMA WAEstablished Series
TAXONOMIC CLASS: Coarse-silty, mixed, superactive, acid, mesic Sulfic Endoaquepts
TYPICAL PEDON: Tacoma silt loam-pasture. (Colors are for moist soil unless otherwise noted.)
Oi--0 to 3 inches; matt of fine grass roots.
A--3 to 10 inches; dark brown (10YR 3/3) silt loam, grayish brown (10YR 5/2) dry; many medium distinct brown (7.5YR 4/4) mottles; moderate fine angular blocky structure; slightly hard, friable; nonsticky and slightly plastic; many medium and fine roots; extremely acid (pH 4.4); abrupt smooth boundary. (6 to 9 inches thick)
Bg1--10 to 26 inches; dark grayish brown (10YR 4/2) silt loam, light brownish gray (10YR 6/2) dry; many fine distinct dark yellowish brown (10YR 4/4) mottles; moderate medium prismatic structure; hard, friable; slightly sticky and slightly plastic; many medium and fine roots; extremely acid (pH 4.3); abrupt smooth boundary. (12 to 18 inches thick)
Bg2--26 to 43 inches; dark grayish brown (10YR 4/2) silt loam, light brownish gray (10YR 6/2) dry; many fine distinct dark yellowish brown (10YR 4/4) redox concentrations; weak medium prismatic structure; hard, friable, nonsticky and slightly plastic; few fine roots; extremely acid (pH 4.2); clear smooth boundary. (14 to 18 inches thick)
Cg1--43 to 53 inches; grayish brown (10YR 5/2) silt loam, gray (10YR 6/1) dry; massive; hard, friable, slightly sticky and slightly plastic; extremely acid (pH 4.4); abrupt smooth boundary. (0 to 12 inches thick)
2Cg2--53 to 63 inches; dark greenish gray (5GY 4/1) clay; common medium distinct brown (7.5YR 4/4) redox concentrations; massive; very hard, friable, very sticky and very plastic; few fine tubular pores; strongly acid (pH 5.4).
TYPE LOCATION: Thurston County, Washington; soil pit in the lower Nisqually delta; NW1/4SE1/4SE1/4 of sec. 31, R. 19 N., R. 1 E.
RANGE IN CHARACTERISTICS: These soils are saturated with water and have a water table near the surface during the winter months and wet periods throughout the year unless they have been artificially drained. The mean annual soil temperature is 47 to 54 degrees F. The soil is more than 60 inches deep, but rooting depth, other than hydrophytes, is limited by the water table. Some pedons have layers of muck 1 to 4 inches thick with a cumulative total of less than 16 inches. The weighted organic carbon content is less than 12 percent in the control section. The particle-size control section has 10 to 18 percent clay by weighted average. Below the Ap horizon, reaction is extremely acid to strongly acid throughout.
The A or Ap horizon has hue of 10YR, through 5Y, value of 3 or 4 moist, 5 through 7 dry, and chroma of 1 or 2 moist. Redox concentrations are faint to distinct. Structure is weak or moderate blocky and less than 15 percent sand coarser than very fine sand.
The Bg horizons have hue of 10YR, 2.5Y, 5Y, or neutral, value of 3 through 6 moist, 4 through 8 dry, and chroma of 0 through 2 moist and dry. Redox concentrations are faint to prominent. Structure is moderate blocky or prismatic. It is silt loam or very fine sandy loam.
The 2Cg horizon is stratified, individual layers range from clay to sand and varies within short distances. Depth to the 2C horizon is more than 60 inches in some pedons.
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING: Tacoma soils are on tidal flats, flood plains at the mouth of rivers on deltas. Slopes are 0 to 2 percent. Elevation is 0 to 20 feet. The soils formed in alluvial deposits and thin layers of organic matter. Many areas have been diked to keep the sea water out. Average annual precipitation ranges from 25 to 60 inches. Mean January temperature is 38 degrees F; mean July temperature is 64 degrees F. The mean annual air temperature is 46 to 52 degrees F. The frost-free season is 160 to 200 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Eliza and the Mt. Vernon soils and Puget soils. Mt. Vernon soils are coarse-loamy and have a xeric moisture regime. Puget soils are nonacid and lack organic lenses.
DRAINAGE AND PERMEABILITY: Very poorly drained; ponded to very slow runoff; moderately slow permeability. These soils are subject to frequent, brief flooding unless protected. An apparent water table is as high as +1 to 0 feet.
USE AND VEGETATION: Most are drained and protected from flooding and used for cropland. Some areas are now in sedges, grasses, and rushes, but were formerly in improved pasture. Native vegetation is red alder, western redcedar, Sitka spruce, and black cottonwood with an understory of western brackenfern, western swordfern, devils club, Indian plum, Douglas spirea, willow, saltgrass, sedges, and rushes.
DISTRIBUTION AND EXTENT: Puget Sound Area of Western Washington. The series is of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Pierce County, Washington, 1945.
REMARKS: Sample number R72230-233. Diagnostic horizons and features recognized in this pedon are an ochric epipedon from the mineral surface to 10 inches, a cambic horizon from 10 to 43 inches and a substratum with an irregular decrease of organic carbon with depth and sulfidic material from 10 to 63 inches.