LOCATION SWEM WA
Established Series
Rev. SBC/RFP/RJE/TLA
05/2012
SWEM SERIES
The Swem series consists of very deep, moderately well drained soils formed in basalt colluvium mixed with volcanic ash over marine sediments. Swem soils are on old earthflows and have slopes of 0 to 65 percent. The average annual precipitation is about 100 inches and average annual temperature is about 50 degrees F.
TAXONOMIC CLASS: Medial over loamy, ferrihydritic over isotic, mesic Aquic Fulvudands
TYPICAL PEDON: Swem gravelly medial silt loam - forested. (Colors are for moist soil unless otherwise noted. Textures are apparent field textures.)
0i--0 to 0.5 inch; slightly decomposed loose litter of needles and twigs.
0e--0.5 to 1.5 inches; moderately decomposed litter.
A--1.5 to 16 inches; very dark brown (10YR 2/2) gravelly medial silt loam, very dark grayish brown (10YR 3/2) dry; moderate fine and medium subangular blocky structure; hard, firm, slightly sticky and slightly plastic; weakly smeary; few coarse, common medium, and many very fine roots; few very fine tubular pores; 20 percent angular basalt gravel; strongly acid (pH 5.4); clear wavy boundary. (10 to 20 inches thick)
Bw1--16 to 29 inches; yellowish brown (10YR 5/6) gravelly medial silt loam, brownish yellow (10YR 6/6) dry; few fine prominent grayish brown (10YR 5/2) redox depletions, very pale brown (10YR 8/3) dry; moderate medium subangular blocky structure; slightly hard, friable, slightly sticky, slightly plastic; weakly smeary; few fine and very fine roots; few very fine tubular pores; 20 percent angular basalt gravel, 10 percent rounded basalt cobbles; moderately acid (pH 5.8); gradual smooth boundary. (11 to 23 inches thick)
2Bw2--29 to 61 inches; yellowish brown (10YR 5/6) paragravelly silt loam, yellow (10YR 7/6) dry; common medium prominent grayish brown (10YR 5/2) redox depletions, very pale brown (10YR 8/3) dry; moderate medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; few very fine roots; few very fine tubular pores; 25 percent soft siltstone paragravel; strongly acid (pH 5.4).
TYPE LOCATION: Pacific County, Washington; on D-line logging road about 1 mile northeast of the intersection with the A-line logging road; approximately 2,000 feet east, 750 feet south of the northwest corner, sec. 27, T. 11 N., R. 9 W.
RANGE IN CHARACTERISTICS: The mean annual soil temperature is 47 to 52 degrees F. The difference between the mean summer and mean winter soil temperature is 5 to 9 degrees F. The upper part of the particle-size control section has 15 to 35 percent gravel, cobbles, and stone-size basalt fragments and the lower part has 10 to 80 percent siltstone paragravel. Depth to unconformable marine sediments is 20 to 40 inches. Hue of 7.5YR or 10YR. The umbric epipedon is 10 to 20 inches thick. Redox depletions with a chroma of 2 or less are at a depth of 10 to 20 inches. The particle-size control section has 18 to 27 percent apparent clay. The soil ranges from moderately acid to very strongly acid.
The A horizon has value of 2 or 3 moist, 2 to 5 dry and chroma of 2 or 3 moist and dry. It has granular or subangular blocky structure.
The Bw horizon has value of 3 to 5 moist, 3 to 6 dry, and chroma of 3 to 7 moist or dry. It is gravelly silt loam, cobbly silt loam, gravelly loam, gravelly silty clay loam, or cobbly loam.
The 2Bw horizon, or 2BC horizon when present, has value of 3 to 6 moist, 5 to 7 dry, chroma of 2 to 6 moist or dry. It is silt loam, silty clay loam, clay loam, or loam. Some pedons lack a 2Bw horizon and have a massive 2BC horizon.
COMPETING SERIES: These are the similar
Ozette and
Sylvia series. Ozette soils have 10 to 30 percent hard rock fragments throughout the particle-size control section and 4 to 7 percent organic carbon throughout the upper two-thirds of the particle-size control section. Sylvia soils have 35 to 50 percent apparent clay and lack rock fragments in the particle-size control section.
GEOGRAPHIC SETTING: Swem soils are on old extensive earthflows at elevations from 500 to 2,000 feet. Slopes range from 0 to 65 percent. Swem soils formed in material weathered from a mixture of colluvial basalt and volcanic ash over marine sediments. They are in a coastal marine climate with cool wet winters and cool dry summers. Mean annual precipitation is 70 to 120 inches. The mean January temperature is 38 degrees F.; the mean July temperature is 60 degrees F.; and the mean annual temperature is 50 degrees F. The growing season (28 degrees F) is about 200 to 240 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the
Astoria,
Boistfort,
Bunker,
Elochoman,
Lytell,
Willapa and
Zenker soils. All of these soils lack redox depletions with a chroma of 2 or less within 20 inches of the surface.
DRAINAGE AND PERMEABILITY: Moderately well drained; slow to rapid runoff; moderately slow permeability. Depth to a perched seasonal water table is 2.5 to 3.5 feet from November to April.
USE AND VEGETATION: Swem soils are used for timber production, wildlife habitat and recreation. Vegetation is mainly a Douglas-fir and western hemlock forest, and some red alder, bigleaf maple, western redcedar, and Sitka spruce with an understory of vine maple, red huckleberry, Pacific trillium, Oregon oxalis, western brackenfern, Oregon-grape, salal, western swordfern, and salmonberry.
DISTRIBUTION AND EXTENT: Southwestern Washington. The series is moderately extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Pacific County, Washington, 1978.
REMARKS: Diagnostic horizons and features recognized in this pedon are: an umbric epipedon from the mineral surface to 15 inches and a cambic horizon with grayish redox depletions from 15 to 60 inches. The bulk density of these soils is 0.60 to 0.90 g/cc in the upper 20 to 40 inches and 0.90 to 1.20 g/cc throughout the rest of the profile.
National Cooperative Soil Survey
U.S.A.