LOCATION DORB                    ID

Established Series
Rev. CJW/AVY/EMM
10/2013

DORB SERIES

The Dorb series consists of deep, well drained soils on plateaus, terrace escarpments and canyonsides. They formed in volcanic ash overlying basalt bedrock. Slope ranges from 5 to 65 percent. The average annual temperature is about 43 degrees F., and the average annual precipitation is about 30 inches.

TAXONOMIC CLASS: Ashy-skeletal over loamy-skeletal, glassy over isotic, frigid Typic Udivitrands

TYPICAL PEDON: Dorb stony ashy silt loam, forest, on a north-facing slope of 65 percent at 2720 feet elevation. When described on April 20, 1982, the soil was moist throughout. (Colors are for dry soil unless otherwise noted.)

Oi--0 to 1 inch; slightly decomposed needles, twigs, and moss.

Oe--1 to 2 inches; decomposed organic matter mixed with recent Mt. St. Helen's volcanic ash.

A--2 to 5 inches; yellowish brown (10YR 5/4) stony ashy silt loam, dark yellowish brown (10YR 3/4) moist; weak very fine and fine granular structure; soft, very friable, nonsticky and slightly plastic; common very fine, fine, medium, and coarse roots; many very fine, fine and few medium tubular pores; 10 percent gravel and 5 percent cobbles; about 0.1 percent stones on the surface; neutral (pH 6.8); clear wavy boundary. (0 to 4 inches thick.)

Bw1--5 to 15 inches; light yellowish brown (10YR 6/4) cobbly ashy silt loam, dark yellowish brown (10YR 4/4) moist; weak fine and medium subangular blocky structure; soft, very friable, nonsticky and slightly plastic; common very fine, fine, medium, and coarse roots; many very fine, fine, and few medium tubular pores; 10 percent gravel, 15 percent cobbles; slightly acid (pH 6.5); clear wavy boundary. (7 to 11 inches thick)

Bw2--15 to 28 inches; light yellowish brown (10YR 6/4) very stony ashy silt loam, dark yellowish brown (10YR 4/4) moist; weak medium and coarse subangular blocky structure; soft, very friable, nonsticky and slightly plastic; few very fine, fine, medium, and coarse roots; common very fine and fine tubular pores; 10 percent gravel, 20 percent cobbles, 20 percent stones; slightly acid (pH 6.5); clear wavy boundary. (8 to 15 inches thick)

Bw3--28 to 36 inches; light yellowish brown (10YR 6/4) extremely stony ashy silt loam, dark yellowish brown (10YR 4/4) moist; weak medium and coarse subangular blocky structure; slightly hard, friable, nonsticky and slightly plastic; few very fine, fine, and medium roots; common very fine and few fine tubular pores; 25 percent gravel, 20 percent cobbles, 30 percent stones; slightly acid (pH 6.3); abrupt wavy boundary. (4 to 10 inches thick)

2C--36 to 52 inches; light yellowish brown (10YR 6/4) extremely stony silt loam, dark yellowish brown (10YR 4/4) moist; massive; slightly hard, friable, nonsticky and slightly plastic; few very fine and fine roots; common very fine and few fine tubular pores; 20 percent gravel, 30 percent cobbles, 35 percent stones; slightly acid (pH 6.3); abrupt irregular boundary. (16 to 18 inches thick)

2R--52 inches; hard, fractured basalt.

TYPE LOCATION: Benewah County, Idaho; about 4.5 miles southeast of St. Maries, about 100 feet west and 1250 feet south of the northeast corner of section 7, T. 45 N., R. 1 W.

RANGE IN CHARACTERISTICS:

Depth to bedrock - 40 to 60 inches
Surface stones - 0 to 0.1 percent
Reaction - slightly acid or neutral throughout
Soil moisture - dry, August and September (25 to 35 days); moist, mid-September through July
Average annual soil temperature - 42 to 45 degrees F.
Average summer soil temperature - 47 to 50 degrees F. with an O horizon

Volcanic ash mantle - 20 to 36 inches thick
Volcanic glass content in the 0.02 to 2.0 mm fraction - 30 to 65 percent
Acid-oxalate extractable Al plus 1/2 Fe - 1.0 to 3.0 percent
Phosphate retention - 55 to 90 percent
15-bar water tension on air dried samples - 7 to 12 percent

A horizon
Value - 4 to 6 dry, 2 or 3 moist
Chroma - 2 to 4 dry or moist
Rock fragments - 5 to 25 percent
Bulk density - 0.65 to 0.85 g/cc

Bw horizon
Hue - 10YR or 7.5YR
Value - 5 or 6 dry, 3 or 4 moist
Chroma - 3 or 4 dry or moist
Textures - ashy loam or ashy silt loam)
Rock fragments - 5 to 45 percent in the upper part and 45 to 85 percent in the lower part
Bulk density - 0.65 to 0.85 g/cc

2Bw horizon - present in some pedons
Chroma - 3 or 4 dry or moist
Textures - loam or silt loam
Rock fragments - 35 to 85 percent
Bulk density - 0.75 to 1.10 g/cc

2BC present in some pedons

2C horizon
Chroma - 3 or 4 dry or moist
Texture - loam or silt loam
Rock fragments - 65 to 85 percent

COMPETING SERIES: There are no competing series.

GEOGRAPHIC SETTING: Dorb soils are on north aspects of plateaus, terrace escarpments, and canyonsides. Slopes range from 5 to 65 percent. These soils formed in volcanic ash overlying basalt. Elevation ranges from 2,100 to 3,200 feet. The average annual air temperature ranges from to 45 degrees F. and the average annual precipitation is 25 to 35 inches. The average frost-free period is from 80 to 110 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Agatha, Ahrs, Blinn, Bobbitt, Chatcolet, Honeyjones, Lacy, and Sly soils. The Ahrs and Honeyjones soils are on mountainsides and are very deep. Chatcolet and Sly soils are on terraces and have argillic horizons. The Agatha and Blinn soils occupy east and west aspects and the Bobbitt and Lacy soils occupy south aspects of terrace escarpments, and all are loamy-skeletal.

DRAINAGE AND PERMEABILITY: Well drained; medium to rapid runoff; saturated hydraulic conductivity is moderately high.

USE AND VEGETATION: These soils are used for timber production, livestock grazing, recreation, wildlife habitat, and watershed. Potential natural vegetation is mainly western hemlock, western redcedar, grand fir, western larch, western white pine, Douglas-fir, and lodgepole pine, with an understory of queencup beadlily, myrtle pachystima, goldthread, starry false-Solomon's-seal, northern twinflower, oneleaf foamflower, American trailplant, fairybells, darkwoods violet, and western rattlesnake plantain.

DISTRIBUTION AND EXTENT: Northern Idaho. This soil is not extensive.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana

SERIES ESTABLISHED: Benewah County, Idaho, 1975.

REMARKS: Diagnostic horizons and features recognized in this pedon are:

Ochric epipedon - the zone from the soil surface to 5 inches (Oi, Oe and A horizons)

Cambic horizon - the zone from 5 to 36 inches (Bw1, Bw2 and Bw3 horizons)

Volcanic ash mantle - the zone 2 to 36 inches (A, Bw1, Bw2 and Bw3 horizons)

Particle-size control section - the zone from 2 to 42 inches (A, Bw1, Bw2, Bw3 and part of the 2C horizons)

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National Cooperative Soil Survey
U.S.A.