LOCATION THRAPP WAEstablished Series
TAXONOMIC CLASS: Coarse-loamy, isotic, frigid Vitrandic Haploxerolls
TYPICAL PEDON: Thrapp ashy loam, on a northeast facing 19 percent slope at an elevation of 2,900 feet in a Douglas-fir and ponderosa pine forest. (Colors are for dry soil unless otherwise stated. All textures are apparent field textures.)
Oe--0 to 1 inch; moderately decomposed needles, twigs, and leaves; abrupt smooth boundary. (1 to 3 inches thick)
A1--1 to 5 inches; very dark grayish brown (10YR 3/2) ashy loam, very dark brown (10YR 2/2) moist; weak fine and medium subangular blocky structure parting to moderate fine granular; soft, very friable, nonsticky and nonplastic; many very fine and fine and few medium and coarse roots; common fine tubular pores; neutral (pH 6.8); clear wavy boundary.
A2--5 to 13 inches; very dark grayish brown (10YR 3/2) ashy loam, very dark brown (10YR 2/2) moist; weak fine and medium subangular blocky structure; soft, very friable, nonsticky and nonplastic; many very fine and fine and few medium and coarse roots; common fine tubular pores; neutral (pH 6.8); clear smooth boundary. (Combined A horizon thickness is 10 to 15 inches.)
2Bw--13 to 23 inches; light brownish gray (10YR 6/2) sandy loam, grayish brown (10YR 5/2) moist; weak medium subangular blocky structure; soft, very friable, nonsticky and nonplastic; common very fine and fine roots; common fine irregular pores; 5 percent gravel; slightly acid (pH 6.4); clear wavy boundary. (8 to 12 inches thick)
2C1--23 to 30 inches; very pale brown (10YR 7/3) gravelly sandy loam, pale brown (10YR 6/3) moist; massive; soft, very friable, nonsticky and nonplastic; few very fine and fine roots; common very fine and fine irregular pores; 15 percent gravel; slightly acid (6.4); gradual wavy boundary.
2C2--30 to 37 inches; very pale brown (10YR 7/3) gravelly sandy loam, pale brown (10YR 6/3) moist; massive; soft, very friable, nonsticky and nonplastic; few very fine and fine roots; common very fine and fine irregular pores; 20 percent gravel; slightly acid (6.4); clear smooth boundary. (combined 2C horizon thickness is 10 to 18 inches)
2Cd--37 to 61 inches; very pale brown (10YR 8/2) gravelly sandy loam, light gray (10YR 7/2) moist; 30 percent fine and medium distinct yellowish brown (10YR 5/6) moist irregular shaped redox concentrations in the upper part; massive, hard, friable, slightly sticky and nonplastic; few very fine roots; 20 percent gravel; slightly acid (pH 6.2).
TYPE LOCATION: Okanogan County, Washington, about 8 miles southeast of Twisp, Washington; 2,100 feet east and 700 feet south of the northwest corner of section 18, T. 32 N., R. 23 E. (Latitude 48 degrees, 17 minutes, 15 seconds N., Longitude 120 degrees, 00 minutes, 13 seconds W.)
RANGE IN CHARACTERISTICS: The mean annual soil temperature is 42 to 45 degrees F. These soils are usually moist but are dry in all parts of the moisture control section for 60 to 75 days following the summer solstice. The mollic epipedon is 10 to 15 inches thick and has an estimated moist bulk density of 1.10 to 1.30 g/cc, volcanic glass content of 5 to 20 percent, acid-oxalate extractable aluminum plus one-half of the acid-oxalate extractable iron of 0.4 to 1.0 percent, and 15-bar water retention of 5 to 10 percent for air dried samples. The particle-size control section averages 15 to 30 percent rock fragments and 6 to 15 percent clay. Depth to the 2Cd (densic material) and redox concentrations is 35 to 45 inches.
The A horizon has values of 3 or 4 dry, 2 or 3 moist.
The 2Bw horizon has values 5 or 6 dry, 4 or 5 moist, and chromas of 2 or 3 dry or moist. It has 0 to 15 percent gravel. Reaction is slightly acid to neutral.
The 2C horizons have values of 6 or 7 dry, 5 or 6 moist, and chromas of 2 or 3 dry or moist. It is gravelly sandy loam or gravelly coarse sandy loam. It has 15 to 30 percent gravel.
The 2Cd horizon has values of 6 to 8 dry and 6 or 7 moist. It is gravelly sandy loam or gravelly coarse sandy loam. It can be gravelly loamy sand below 45 inches. It has 10 to 30 percent gravel.
COMPETING SERIES: These are the Bunchpoint, Dinkelman, Kilmerque, Lostcreek, and Republic series. The Dinkelman soils are 40 to 60 inches to a paralithic contact. Kilmerque soils are 20 to 40 inches to a paralithic contact. Republic soils are well drained and are very deep. Bunchpoint soils are 20 to 40 inches to a lithic contact. Lostcreek soils are very deep.
GEOGRAPHIC SETTING: Thrapp soils are on toeslopes and drainage sideslopes of glaciated mountains. Slopes are 5 to 35 percent. These soils form in till and some glaciofluvial material with a component of volcanic ash in the upper part. Elevations range from 2,000 to 3,800 feet. The climate is characterized by warm, dry summers and cool, moist winters. The average annual precipitation is 20 to 24 inches. The mean January temperature is 23 degrees F, the mean July temperature is 65 degrees F, and the mean annual temperatures is 40 to 44 degrees F. The frost-free season is 90 to 130 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Enson, Merkel, and Nevine soils. Enson soils are on footslopes and backslopes and have a lighter-colored surface. Merkel soils are on footslopes and backslopes and are loamy-skeletal. Nevine soils are on north facing backslopes with a volcanic ash mantle greater than 14 inches thick.
DRAINAGE AND PERMEABILITY: Moderately well drained; medium runoff; moderately rapid above 2Cd horizon, moderately slow through 2Cd horizon. Thrapp soils have a perched water table from March to June at a depth of 36 to 45 inches.
USE AND VEGETATION: Used for timber production, wildlife habitat, watershed, and recreation. Native vegetation is Douglas-fir and ponderosa pine with an understory of common snowberry, pinegrass, Saskatoon serviceberry, mountainlover, heartleaf arnica, and shinyleaf spirea.
DISTRIBUTION AND EXTENT: Northcentral Washington. This 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:
Mollic epipedon - 1 to 13 inches (A1 and A2 horizon)
Cambic horizon - 13 to 23 inches (Bw horizon)
PSCS - zone from 11 to 37 inches
Vitrandic properties from 1 to 13 inches.