LOCATION ILWACO WAEstablished Series
TAXONOMIC CLASS: Medial, ferrihydritic, isomesic Typic Fulvudands
TYPICAL PEDON: Ilwaco medial silt loam, forested. (Colors are for moist soil unless otherwise noted. All textures are apparent field textures.)
Oi--0 to 2 inches; slightly decomposed accumulation of needles, twigs, mosses, and roots; abrupt smooth boundary.
A1--2 to 13 inches; dark brown (10YR 3/3) medial silt loam, brown (10YR 5/3) dry; moderate fine granular structure; slightly hard; very friable, nonsticky, slightly plastic and weakly smeary; many very fine and fine, common medium and coarse roots; many very fine and fine interstitial pores; moderately acid (pH 5.6); gradual wavy boundary. (7 to 12 inches thick)
A2--13 to 19 inches; dark brown (10YR 3/3) medial silt loam, yellowish brown (10YR 5/4) dry; moderate fine and medium subangular blocky structure; slightly hard, very friable, slightly sticky, slightly plastic and weakly smeary; common fine and very fine, few coarse roots; many very fine and fine tubular pores; strongly acid (pH 5.4); clear wavy boundary. (5 to 8 inches thick)
Bw1--19 to 34 inches; dark yellowish brown (10YR 4/4) medial silt loam, brownish yellow (10YR 6/6) dry; weak medium subangular blocky structure; slightly hard, friable, slightly sticky, slightly plastic and weak smeary; common very fine and fine roots; many very fine and fine tubular pores; strongly acid (pH 5.4); gradual wavy boundary. (12 to 16 inches thick)
Bw2--34 to 62 inches; dark yellowish brown (10YR 4/6) medial silt loam, brownish yellow (10YR 6/6) dry; weak medium subangular blocky structure; slightly hard, friable, slightly sticky, slightly plastic and weakly smeary; few very fine roots; many very fine tubular pores; moderately acid (pH 6.0).
TYPE LOCATION: Pacific County, Washington; on logging road, approximately 1,800 feet north, 2,200 feet west of the SE corner sec. 25, T.14N., R.10W.
RANGE IN CHARACTERISTICS: The solum is 50 to more than 60 inches thick, and depth to soft sandstone exceeds 60 inches. Mean annual soil temperature is 47 to 49 degrees F. The difference between the mean summer and mean winter soil temperature is 5 to 9 degrees F. The particle-size control section has moist bulk density of 0.60 to 0.90 g/cc; acid oxalate extractable aluminum plus one-half the iron of 2.0 to 4.0 percent, phosphate retention of 85 to 100 percent, 20 to 27 percent clay and 0 to 15 percent paragravel sandstone fragments. It is very strongly acid to moderately acid. The umbric epipedon is 12 to 20 inches thick.
The A horizon has hue of 10YR or 7.5YR, value of 2 or 3 moist, 4 to 5 dry and chroma of 2 or 3 moist, 2 through 4 dry. It has moderate or strong granular or subangular blocky structure. It has 7 to 15 percent organic matter.
The B horizon has hue of 10YR or 7.5YR, value of 3 through 5 moist, 4 through 6 dry, and chroma of 4 through 6 moist and dry. It is medial silt loam or medial loam and has angular and subangular blocky structure.
COMPETING SERIES: These are the Astoria, Boistfort, Bunker, Elochoman, Kinney, Knappton, Lebam, Le Bar, Lytell, Narel, Palix, Silcox, Swem, Sylvia, Vesta, Wahkiakum, Wellman, Willapa, and Zenker series. Astoria, Boistfort, Lebam, and Vesta soils have more than 35 percent clay in the control section. Bunker, Kinney, and Knappton soils have more than 15 percent hard rock fragments. Elochoman and Le Bar soils have less than 4 percent organic carbon in the upper part of the control section. Lytell and Palix soils have more than 35 percent soft siltstone fragments in the control section. Narel and Zenker soils have 40 to 70 percent soft sandstone fragments in the control section. Silcox soils are moderately coarse textured. Swem soils are moderately well drained and have more than 15 percent hard rock fragments (gravel size) in the A and upper B horizons. Sylvia and Willapa soils have mottles with chroma of 2 or less in the control section. Wahkiakum soils have hue of 2.5YR or 5YR in the upper part of the control section, are neutral to medium acid, and have hard rock fragments in the control section.
GEOGRAPHIC SETTING: Ilwaco soils are on uplands at elevations from sea level to 1,000 feet. These soils occupy broad ridgetops, small plateaus, and back and shoulder slopes. Slopes are 1 to 65 percent. The soils formed in material from deeply weathered sandstone. The climate is marine influenced, characterized by cool, wet winters, and cool, dry summers. The mean annual precipitation is 80 to 110 inches. The mean January temperature is 38 degrees F.; mean July temperature is 60 degrees F.; and the mean annual temperature is 48 degrees F. The growing season (28 degrees F.) is 180 to 220 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Knappton, Lebam, Narel, Palix, Vesta, and Willapa soils.
DRAINAGE AND PERMEABILITY: Well drained; slow to medium runoff; moderate permeability.
USE AND VEGETATION: Timber production, wildlife habitat, and recreation are the principal uses for this soil. The major commercial tree species is western hemlock, with scattered Sitka spruce, western red cedar, and red alder. Understory species are salal, oxalis, swordfern, brackenfern, salmonberry, blackberry, red elderberry, and vine maple.
DISTRIBUTION AND EXTENT: Southwestern Washington; MLRA 4A. The series is of small extent.
MLRA OFFICE RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Pacific County, Washington, 1978.
REMARKS: Diagnostic horizons and other features
Umbric epipedon - from 2 to 19 inches
Cambric horizon - from 19 to 62 inches
The cool phase map units characterized by having Pacific Silver Fir are considered to be isofrigid.
ADDITIONAL DATA: National Soil Survey Laboratory, Lincoln, Nebraska data are available on this soil: sample number S77WA-25-5.