LOCATION TWINSI WAEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, magnesic Typic Humicryods
TYPICAL PEDON: Twinsi very gravelly loam - on a 45 percent west facing convex slope under a forest canopy of mountain hemlock and Pacific silver fir at 3,500 feet elevation. (Colors are for moist soil unless otherwise noted. All textures are apparent field textures.)
Oi--8 to 2 inches; undecomposed needles, twigs and bark.
Oa--2 inches to 0; decomposed organic mat; many very fine, fine, medium, and common coarse roots.
E--0 to 1 inch; brown (7.5YR 5/2) gravelly fine sandy loam, pinkish gray (7.5YR 7/2) dry; weak medium subangular blocky parting to weak fine granular structure; soft, very friable, nonsticky, nonplastic; many very fine, fine, medium and common coarse roots; many very fine irregular pores; 30 percent pebbles; NaF pH less than 9.0; very strongly acid (pH 4.6); abrupt smooth boundary. (1 to 2 inches thick)
Bhs--1 to 6 inches; strong brown (7.5YR 4/6) very gravelly loam, reddish yellow (7.5YR 6/6) dry; dark reddish brown (5YR 3/3) organic stains on ped faces, reddish brown (5YR 4/4) dry; weak medium subangular blocky parting to weak medium granular structure; soft, very friable, nonsticky, nonplastic, weakly smeary, many fine, medium, and common very fine and coarse roots; many very fine irregular pores; 30 percent pebbles and 10 percent cobbles; NaF pH 11.0; strongly acid (pH 5.2); clear wavy boundary. (2 to 5 inches thick)
Bs1--6 to 14 inches thick; strong brown (7.5YR 4/6) very gravelly loam, reddish yellow (7.5YR 6/6) dry; moderate medium subangular blocky structure; slightly hard, friable, slightly sticky, nonplastic, weakly smeary; few very fine and fine roots; common very fine irregular pores; 40 percent pebbles and 15 percent cobbles; NaF pH 10.5; strongly acid (pH 5.4); clear irregular boundary. (3 to 12 inches thick)
Bs2--14 to 22 inches; dark yellowish brown (10YR 4/4) very gravelly loam, light yellowish brown (10YR 6/4); weak coarse subangular blocky structure; slightly hard, friable, slightly sticky, slightly plastic, weakly smeary; very few very fine and fine roots; common very fine irregular pores; 40 percent pebbles and 15 percent cobbles; NaF pH 10.0; strongly acid (pH 5.4); abrupt smooth boundary. (1 to 10 inches thick)
C--22 to 27 inches; grayish brown (2.5Y 5/2) very gravelly sandy loam, light brownish gray (2.5Y 6/2) dry; massive; slightly hard, friable, nonsticky, nonplastic; few very fine irregular pores; 40 percent pebbles and 10 percent cobbles; NaF pH 9.8; slightly acid (pH 6.2); abrupt smooth boundary. (4 to 19 inches thick)
2Cr--27 to 60 inches; dark yellowish brown (10YR 4/4) dense compact glacial till that breaks to very gravelly loam, light yellowish brown (10YR 6/4) dry; massive; hard, firm, nonsticky, nonplastic; few very fine irregular pores; 40 percent pebbles; NaF pH 10.5; slightly acid (pH 6.2).
TYPE LOCATION: Whatcom County, Washington; about 9 miles southeast of Van Zandt; 2400 feet north and 700 feet east of the southwest corner of sec. 3, T. 37 N., R. 6 E.
RANGE IN CHARACTERISTICS: Mean annual soil temperature is 41 to 45 degrees F. Depth to a paralithic contact with dense compact glacial till ranges from 20 to 40 inches. The thickness of the solum is 13 to 30 inches. By weighted average, rock fragments in the control section range from 45 to 75 percent, including 5 to 20 percent cobbles. The Mg-Ca ratio is greater than 20 throughout the control section.
The E horizon has hue of 5YR or 7.5YR, value of 4 or 5 moist, 6 or 7 dry, and chroma of 2 or 3 moist and dry. Reaction is extremely acid, very strongly acid, or strongly acid.
The Bhs horizon has hue of 5YR or 7.5YR, value of 3 through 5 moist, 4 through 7 dry, and chroma of 3 through 6 moist and dry. Organic stains have value of 3 through 5 moist, 3 through 7 dry, and chroma of 2 through 6 moist and dry. It is very gravelly loam or very gravelly silt loam. Reaction is extremely acid to strongly acid.
The Bs horizon has hue of 7.5YR or 10YR, value of 4 or 5 moist, 5 or 6 dry, and chroma of 4 through 6 moist and dry. It averages 35 to 55 percent pebbles and 5 to 20 percent cobbles. It is very gravelly loam, very gravelly sandy loam, or extremely gravelly loam. Reaction is very strongly acid or strongly acid.
The C horizon has hue of 10YR or 2.5Y, value of 3 or 4 moist, 5 through 7 dry, and chroma of 2 through 6 moist and dry. It averages 40 to 70 percent rock fragments. It is very gravelly loam, very gravelly sandy loam, or extremely gravelly loam. Reaction is strongly acid to slightly acid.
The 2Cr horizon is dense glacial till that breaks to very gravelly loam, very gravelly sandy loam, or extremely gravelly sandy loam. It has hue of 10YR or 2.5Y, value of 3 or 4 moist, 5 through 7 dry, and chroma of 2 through 4 moist and dry.
COMPETING SERIES: These are the Jackman and Klawatti soils. Jackman soils are deep. Klawatti soils are 20 to 40 inches deep to a lithic contact..
GEOGRAPHIC SETTING: Twinsi soils are on glacially modified mountain backslopes and shoulder slopes at elevations of 2,500 to 4,000 feet. Slopes are 30 to 60 percent. The soils formed in colluvium, slope alluvium, and glacial till derived from dunite with an admixture of volcanic ash and loess. Twinsi soils are in a marine climate with cool moist summers and cold wet winters. Snow cover lasts from November through May. Average annual precipitation is 90 to 105 inches. Mean January temperature is about 29 degrees F; mean July temperature is about 57 degrees F. The mean annual temperature is about 41 degrees F. The frost-free season is 85 to 100 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Jackman and Klawatti soils and the Edfro soils. Edfro soils are shallow to a paralithic contact with dense compact glacial till.
DRAINAGE AND PERMEABILITY: Moderately well drained; slow or medium runoff; moderate permeability above the dense glacial till and very slow through it. A perched water table is at 1.5 to 3 feet during December through April.
USE AND VEGETATION: Used for timber production, watershed, recreation, and wildlife habitat. Native vegetation is Pacific silver fir, mountain hemlock, Alaska-cedar, western hemlock, with an undergrowth of tall blue huckleberry, bunchberry dogwood, western brackenfern, deer fern, and longtube twinflower.
DISTRIBUTION AND EXTENT: Twin Sisters area in the Cascade Mountains in Whatcom County, Washington. The series is of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Whatcom County, Washington, 1983.
REMARKS: This draft reflects a change in classification from loamy-skeletal, serpentinitic Andic Cryochrepts to loamy-skeletal, serpentinitic Typic Cryorthods. Diagnostic horizons and features recognized in this pedon are: a spodic horizon from 1 to 20 inches, 45 to 75 percent dunite fragments in the particle-size control section and a paralithic contact at 27 inches. The spodic horizon does not meet chemical criteria for a spodic horizon but does meet micro morphological criteria, i.e. cracked coatings and silt-sized and larger pellets.