LOCATION TWENTYMILE WAEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, isotic Andic Dystrocryepts
TYPICAL PEDON: Twentymile stony ashy fine sandy loam - forestland, on a northeast-facing 23 percent slope at 5,880 feet elevation in a subalpine fir and lodgepole pine forest. (Colors are for dry soil unless otherwise stated. All textures are apparent field textures.)
Oe--0 to 2 inches; partially decomposed needles, leaves and twigs; abrupt smooth boundary. (1 to 3 inches thick)
C--2 to 3 inches; white (10YR 8/1) ashy silt loam, grayish brown (10YR 5/2) moist; weak fine granular structure; soft, very friable, nonsticky, nonplastic and weakly smeary; common very fine and fine roots; common very fine and fine pores; 4 percent pebbles; moderately acid (pH 5.6); clear wavy boundary. (0 to 2 inches thick)
2A--3 to 6 inches; pale brown (10YR 6/3) stony ashy fine sandy loam; brown (10YR 4/3) moist; weak fine subangular blocky structure parting to weak fine granular; soft, very friable, nonsticky, nonplastic and weakly smeary; common very fine and fine roots and common medium and coarse roots; common very fine and fine pores; 5 percent pebbles, 3 percent cobbles, and 10 percent stones; NaF pH 11.0; moderately acid (pH 6.0); clear smooth boundary. (2 to 4 inches thick)
2Bw--6 to 15 inches; light yellowish brown (10YR 6/4) gravelly ashy fine sandy loam; dark yellowish brown (10YR 4/4) moist; weak medium and coarse subangular blocky structure; soft, very friable, nonsticky, nonplastic and weakly smeary; common very fine and fine roots and few medium and coarse roots; common very fine and fine pores; 15 percent pebbles; NaF pH 11.0; slightly acid (pH 6.2); clear smooth boundary. (5 to 10 inches thick)
3CB--15 to 33 inches; light brownish gray (10YR 6/2) very gravelly sandy loam; grayish brown (10YR 5/2) moist; massive; soft, very friable, nonsticky and nonplastic; few very fine and fine roots and few medium roots; common very fine and fine irregular pores; 35 percent pebbles and 5 percent cobbles; slightly acid (pH 6.4); gradual wavy boundary. (10 to 19 inches thick)
3Cd1--33 to 46 inches; light gray (2.5Y 7/2) very gravelly sandy loam, grayish brown (2.5Y 5/2) moist; massive; hard, friable, nonsticky and nonplastic; few very fine roots; few fine irregular pores; 35 percent pebbles, 5 percent cobbles; slightly acid (pH 6.2); gradual wavy boundary.
3Cd2--46 to 62 inches; light brownish gray (2.5Y 6/2) very gravelly sandy loam, grayish brown (2.5Y 5/2) moist; massive; hard, firm, slightly sticky and slightly plastic; common thin olive brown (2.5Y 4/3) moist stains; 30 percent pebbles and 5 percent cobbles; slightly acid (pH 6.4).
TYPE LOCATION: Okanogan County, Washington, about 3.5 miles southwest of Thunder Mountain; 2,300 feet east and 2,100 feet north of the southwest corner of section 10, T. 37N., R. 23 E. (Latitude 48 degrees, 43 minutes, 06 seconds N., Longitude 119 degrees, 56 minutes, 19 seconds W.)
RANGE IN CHARACTERISTICS: The average annual soil temperature is 37 to 42 degrees F. Average summer soil temperature is 42 to 46 degrees F. These soils are usually moist, but are dry for less than 45 days following the summer solstice. Thickness of the volcanic ash is 7 to 14 inches, and has an estimated moist bulk density of 0.75 to 0.90 g/cc, volcanic glass content of 30 to 60 percent, acid-oxalate extractable aluminum plus one-half of the acid-oxalate extractable iron of 1.0 to 2.0 percent, and 15-bar water retention of 8 to 12 percent for air dried samples. Depth to dense till is 20 to 35 inches. The particle-size control section averages 35 to 60 percent rock fragments and 3 to 10 percent clay.
The C horizon has values of 7 or 8 dry, 5 or 6 moist, and chromas of 1 or 2 dry. It is absent in some pedons.
The 2A horizon has value of 5 or 6 dry, 3 or 4 moist and chroma of 3 or 4 dry and moist. It is ashy fine sandy loam or stony ashy fine sandy loam. It has 0 to 10 percent pebbles, 0 to 5 percent cobbles, and 0 to 15 percent stones. Reaction is moderately acid to slightly acid.
The 3CB horizon has hue of 2.5Y or 10YR, value of 6 or 7 dry and chroma of 2 or 3 dry and moist. It is very gravelly sandy loam, very cobbly sandy loam or very stony sandy loam. It averages 35 to 60 percent rock fragments, with 25 to 40 percent pebbles, 3 to 25 percent cobbles and 0 to 20 percent stones. Reaction is slightly acid to neutral.
The 3Cd horizons have hue of 2.5Y or 5Y, value of 6 or 7 dry and chroma of 2 or 3 dry and moist. It is very gravelly sandy loam, very cobbly sandy loam or very stony sandy loam. It averages 35 to 60 percent rock fragments, with 25 to 40 percent pebbles, 3 to 25 percent cobbles and 0 to 20 percent stones. Reaction is slightly acid to neutral.
COMPETING SERIES: These are the Ashworth, Bordengulch, Buhrig, Buttoncreek (T), Deserter (T), Devore, Finney, Gatewall, Hun, Moses, Myerscreek, Otwin, Petty, Phillcher, Prouty, Remmel, Rubycreek (T), Rumsey (T), Skinwood (T), Snowcreek (T), Surgh, Threebutte, Vandamine (T), Venson, and Waldbillig series. Ashworth soils has Bk horizon and lack Cd horizon. Bordengulch, Prouty, Skinwood, Threebutte, and Venson soils are 20 to 40 inches to a lithic contact. Buhrig, Devore, Otwin, and Snowcreek soils are dry for greater than 45 consecutive days following the summer solstice and are 20 to 40 inches to a lithic contact. Buttoncreek soils are dry for greater than 45 days and lack Cd horizons. Finney and Surgh soils are dry for greater than 45 days and are 40 to 60 inches to a lithic contact. Gatewall and Myerscreek soils are dry for greater than 45 days. Hun soils are dry for greater than 45 days and are 40 to 60 inches to a paralithic contact. Moses soils are dry for greater than 45 days and are 20 to 40 inches to a paralithic contact. Rubycreek has a Bt horizon and lacks Cd horizon. Rumsey soils have a ustic moisture regime, have Bk horizon and lack a Cd horison. Holloway, Petty, Vandamine, and Waldbillig soils have Bt horizons and lack Cd layers. Phillcher soils lack Cd horizons.
GEOGRAPHIC SETTING: The Twentymile soils are on north-facing backslopes, footslopes, and toeslopes of glaciated mountains at elevations of 4,800 to 6,800 feet. Slopes are 15 to 35 percent. These soils formed in dense glacial till with a mantle of volcanic ash 7 to 14 inches thick. Precipitation is 35 to 40 inches. The climate is characterized by cool, moist summers and cold, wet winters. The average January temperature ranges from 18 to 22 degrees F., and the average July temperature ranges from 52 to 58 degrees F. Average annual air temperature is 35 to 40 degrees F. Frost-free period 60 to 85 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Crocamp, Devore, Myerscreek, Sitdown, and Smokejump soils. Crocamp soils are on south-facing slopes and have an umbric epipedon. Devore soils are on shoulders and ridges with west, east, and south aspects. Myerscreek soils are on footslopes, toeslopes, and moraines on drier east and west-facing landforms. Sitdown soils are on outwash terraces and are sandy-skeletal. Smokejump soils are on north-facing shoulders and ridges, and are 20 to 40 inches to bedrock.
DRAINAGE AND PERMEABILITY: Well drained, medium runoff; moderately rapid permeability through the volcanic ash mantle, and moderately slow through the sense till layer.
USE AND VEGETATION: Used for timber production, livestock grazing, wildlife habitat, recreation, and watershed. Native vegetation is subalpine fir, lodgepole pine, and Engelmann spruce with an understory of cascades azalea, grouse whortleberry, Labradoe tea, sidebells wintergreen, blue huckleberry, whortleberry, northwestern sedge, and rattlesnake plantain.
DISTRIBUTION AND EXTENT: Northcentral Washington. Series is of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Okanogan National Forest, Okanogan County, Washington, 2005.
REMARKS: Diagnostic horizons and features recognized in this pedon include:
Mt. St. Helens "T" or "W" ash approximately 450 years ago - 0 to 1 inch (C horizon)
Ochric epipedon
Cambic horizon - 6 to 15 inches
Andic properties - 3 to 15 inches
Dense till - 33 to 62 inches
PSCS - zone from 12 to 33 inches
Udic soil moisture regime.
All depths to diagnostic horizons and features are measured from the top of the first mineral horizon.