LOCATION SIOUXON WA
Established Series
Rev. RLE/JS/RJE/TLA
06/2011
SIOUXON SERIES
The Siouxon series consists of deep, well drained soils formed in residuum and colluvium weathered from volcanic ash and basic igneous rock, primarily andesite. They are on mountainsides and ridgetops at elevations of 300 to 1,800 feet. Slopes are 5 to 90 percent. Average annual precipitation is about 70 inches and average annual temperature is about 49 degrees F.
TAXONOMIC CLASS: Loamy-skeletal, isotic, mesic Andic Humixerepts
TYPICAL PEDON: Siouxon very cobbly medial silt loam - under a coniferous forest on a 56 percent slightly convex east-facing backslope at an elevation of 500 feet. The soil was moist throughout when described. (Colors are for moist soil unless otherwise stated. All textures are apparent field textures.)
Oe--0 to 3 inches; moderately decomposed organic litter including needles, leaves, twigs, bark chips, cones, and roots; abrupt smooth boundary. (1 to 4 inches thick)
A--3 to 17 inches; very dark brown (10YR 2/2) very cobbly medial silt loam, grayish brown (10YR 5/2)dry; weak fine subangular blocky structure; soft, friable, slightly sticky and slightly plastic, weakly smeary; many very fine, fine, medium, and coarse roots; many fine pores; 30 percent shot-like aggregates (2-5mm in diameter); 20 percent angular and subangular gravel and 20 percent cobbles; slightly acid (pH 6.2); clear wavy boundary. (10 to 20 inches thick)
Bw1--17 to 31 inches; dark brown (10YR 3/3) very cobbly loam, pale brown (10YR 6/3) dry; weak fine and medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic, weakly smeary; common very fine, fine, medium, and coarse roots; many fine pores; 20 percent shot-like aggregates (2-5mm in diameter); 20 percent angular and subangular gravel and 35 percent cobbles; moderately acid (pH 6.0); clear wavy boundary.
Bw2--31 to 46 inches; brown (10YR 4/3) extremely cobbly loam, light yellowish brown (10YR 6/4) dry; weak fine and medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic, weakly smeary; common very fine, fine, medium, and coarse roots; common fine pores; 20 percent angular and subangular gravel and 50 percent cobbles; moderately acid (pH 5.8); clear irregular boundary. (Combined thickness of the Bw horizon is 19 to 30 inches)
C--46 to 58 inches; dark yellowish brown (10YR 4/4) extremely cobbly loam, very pale brown (10YR 7/4) dry; massive; slightly hard, friable, slightly sticky and slightly plastic, weakly smeary; common very fine, fine, medium, and coarse roots; common fine pores; 20 percent angular gravel and 65 percent cobbles; moderately acid (pH 5.8); abrupt irregular boundary. (12 to 24 inches thick)
R--58 inches; fractured hard andesite with fines in the fracture planes.
TYPE LOCATION: Cowlitz County, Washington; 2,380 feet south and 1,850 feet east of the northwest corner, sec. 27, T. 6 N., R. 2 E., WM.
RANGE IN CHARACTERISTICS: These soils are usually moist but are dry in the moisture control section for 45 to 60 consecutive days following summer solstice. The mean annual soil temperature is 50 to 52 degrees F. Depth to a lithic contact is 40 to 60 inches. The particle-size control section contains from 50 to 80 percent hard rock fragments, dominantly cobbles. Most fragments are angular or subangular and of local origin, but some rounded gravel and cobbles are in some pedons at lower elevations on slopes adjacent to glaciated valleys. The umbric epipedon is 10 to 20 inches thick. Reaction ranges from slightly acid to moderately acid throughout.
The A horizon has hue of 10YR or 7.5YR; value of 2 or 3 moist, 4 or 5 dry, and chroma of 2 or 3 moist and dry. Pebbles range from 15 to 30 percent and cobbles from 20 to 30 percent.
The Bw horizon has hue of 10YR or 7.5YR; value of 3 or 4 moist, 5 to 7 dry, and chroma of 3 or 4 moist and dry. Texture is very cobbly loam, extremely cobbly loam, very cobbly silt loam, or extremely cobbly silt loam. Pebbles range from 15 to 40 percent and cobbles from 15 to 55 percent.
The C horizon has hue of 10YR or 7.5YR; value of 4 or 5 moist, 5 to 7 dry, and chroma of 3 or 4 moist and dry. Texture is extremely cobbly loam or extremely cobbly silt loam. Pebbles range from 15 to 30 percent and cobbles from 45 to 65 percent.
COMPETING SERIES: These are the
Husum,
Putt,
Schneider, and the similar
Delphi,
Guler, McCarthy, McElroy, and
Washougal series. Husum soils are more than 60 inches deep to bedrock. Putt soils have an umbric epipedon more than 20 inches thick and are weakly cemented below 20 to 30 inches. Schneider soils have an umbric epipedon 20 to 30 inches thick. Delphi soils have 35 to 70 percent rounded rock fragments, dominantly pebbles in the particle-size control section. Guler soils have a mean annual temperature of 47 to 50 degrees F, and are dry for 75 to 90 consecutive days. McCarthy soils are 20 to 40 inches deep to a paralithic contact. McElroy soils are dry for 60 to 75 consecutive days. Washougal soils have an umbric epipedon more than 20 inches thick and have a 2C horizon at a depth of 24 to 40 inches.
GEOGRAPHIC SETTING: Siouxon soils are on mountainsides and ridgetops at elevations of 300 to 1,800 feet. Slopes are 5 to 90 percent. These soils formed in residuum and colluvium weathered from volcanic ash and basic igneous rock, including andesite, andesitic volcanic breccia, and plagioclase or olivine basalt. On slopes adjacent to the glaciated valleys of the Green, Toutle, Coweeman, Kalama, and Lewis Rivers, Siouxon soils are influenced by alpine ablation till. The climate is marine and characterized by hot, dry summers and cool, moist winters. The average annual air temperature is 48 to 50 degrees F. The growing season (28 degrees F) is 175 to 200 days. The average annual precipitation is 60 to 80 inches.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the
Baumgard,
Cinebar,
Gobar,
Mulholland,
Newaukum,
Pheeney,
Schneider,
Wilkeson, and
Xeno soils. Baumgard, Govar and Wilkeson soils are fine-loamy, and Wilkeson soils have an argillic horizon. Cinebar, Mulholland, and Newaukum soils are medial. Pheeney soils are 20 to 40 inches deep to a lithic contact and are frigid. Xeno soils are frigid and fine-loamy.
DRAINAGE AND PERMEABILITY: Well drained, slow to very rapid runoff; moderate permeability.
USE AND VEGETATION: Used mainly for timber production, wildlife habitat, watershed, and recreation. Overstory vegetation is mainly Douglas-fir and some red alder, western hemlock, western redcedar and bigleaf maple. Understory vegetation includes western hemlock, western redcedar, bigleaf maple, and vine maple. Ground vegetation includes western swordfern, salal, Oregon-grape, western brackenfern, thimbleberry, rose, vanillaleaf, insideout flower, bedstraw, minerslettuce, Oregon oxalis, strawberry, redwood violet, western trailplant (pathfinder), and longtube twinflower.
DISTRIBUTION AND EXTENT: West slopes of the Cascade Mountains in Cowlitz and Clark Counties, Washington. The series is moderate in extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Cowlitz County, Washington, 1989.
REMARKS: Diagnostic horizons and features recognized in this pedon are an umbric epipedon from the mineral surface to 14 inches, a cambic horizon from 14 to 43 inches, and a lithic contact at 55 inches. Series needs review for consideration for udic. Occurrence of hemlock indicates no moisture deficient?
All depths to diagnostic horizons and features are measured from the to of the first mineral horizon.
National Cooperative Soil Survey
U.S.A.