LOCATION MCARTHUR                ID

Established Series
Rev. SHB-CJW-EMM
11/2010

MCARTHUR SERIES

The McArthur series consists of very deep, well drained soils on mountains, escarpments and breaklands. They formed in material weathered from schist, gneiss, and granite bedrock with minor amounts of volcanic ash in the surface layers. Permeability is moderately rapid. Slope ranges from 35 to 85 percent. The average annual air temperature is about 45 degrees F. and the average annual precipitation is about 35 inches.

TAXONOMIC CLASS: Loamy-skeletal, micaceous, frigid Vitrandic Humixerepts

TYPICAL PEDON: McArthur gravelly ashy very fine sandy loam, very stony; forest; on a southwest-facing slope of 67 percent at 4,030 feet elevation. When described on August 17, 1995, the soil was dry throughout. (Colors are for dry soil unless otherwise stated.)

Oi--0 to 1.5 inches; needles, leaves, twigs, and cones. (1 to 1.5 inches thick)

Oe--1.5 to 2 inches; decomposed organic matter. (0.5 to 1 inch thick)

A--2 to 3 inches; dark grayish brown (10YR 4/2) gravelly ashy very fine sandy loam, black (10YR 2/1) moist; weak very fine and fine granular structure; soft, very friable, nonsticky and slightly plastic; many very fine and few fine roots; many very fine tubular pores; common very fine mica flakes; 20 percent gravel; about 1 percent stones cover surface; slightly acid (pH 6.2); abrupt wavy boundary. (1 to 2 inches thick)

AB--3 to 9 inches; brown (10YR 4/3) very cobbly ashy very fine sandy loam, very dark grayish brown (10YR 3/2) moist; weak very fine, fine and medium subangular blocky structure; soft, very friable, nonsticky and slightly plastic; many very fine, few fine, medium and coarse roots; many very fine tubular pores; common very fine mica flakes; 15 percent gravel, 20 percent cobbles, and 5 percent stones; strongly acid (pH 5.5); clear wavy boundary. (6 to 10 inches thick)

Bw--9 to 17 inches; yellowish brown (10YR 5/4) very cobbly ashy very fine sandy loam, dark yellowish brown (10YR 3/4) moist; weak very fine and fine subangular blocky structure; soft, very friable, slightly sticky and slightly plastic; many very fine, few fine, medium and coarse roots; many very fine tubular pores; common very fine mica flakes; 20 percent gravel, 30 percent cobbles, and 5 percent stones; strongly acid (pH 5.5); gradual wavy boundary. (8 to 14 inches thick)

C1--17 to 31 inches; yellowish brown (10YR 5/4) very cobbly very fine sandy loam, dark yellowish brown (10YR 3/4) moist; massive; slightly hard, friable, slightly sticky and slightly plastic; common very fine and few fine roots; many very fine tubular and irregular pores; many very fine mica flakes; 30 percent gravel, 20 percent cobbles, and 5 percent stones; strongly acid (pH 5.5); gradual wavy boundary. (14 to 18 inches thick)

C2--31 to 45 inches; yellowish brown (10YR 5/4) very cobbly very fine sandy loam, dark yellowish brown (10YR 3/4) moist; massive; slightly hard, friable, slightly sticky and slightly plastic; few very fine and fine roots; common very fine tubular and irregular pores; many very fine mica flakes; 25 percent gravel, 20 percent cobbles, and 5 percent stones; strongly acid (pH 5.5); gradual wavy boundary. (14 to 18 inches thick)

C3--45 to 57 inches; light yellowish brown (10YR 6/4) very cobbly very fine sandy loam, dark yellowish brown (10YR 4/4) moist; massive; slightly hard, friable, slightly sticky and slightly plastic; few very fine and fine roots; few very fine tubular and irregular pores; many very fine mica flakes; 20 percent gravel, 35 percent cobbles, and 5 percent stones; strongly acid (pH 5.5); gradual wavy boundary. (10 to 14 inches thick)

C4--57 to 60 inches; light yellowish brown (10YR 6/4) very cobbly very fine sandy loam, dark yellowish brown (10YR 4/4) moist; massive; slightly hard, friable, slightly sticky and slightly plastic; few very fine roots; few very fine tubular and irregular pores; many very fine and few fine mica flakes; 15 percent gravel, 20 percent cobbles, and 5 percent stones; strongly acid (pH 5.5).

TYPE LOCATION: Boundary County, Idaho; about 3.5 miles south of Naples, about 1,000 feet north and 1,725 feet east of the southwest corner of sec. 30, T. 60 N., R. 1 E; Latitude - 48 degrees, 31 minutes, 03 seconds North;
Longitude - 116 degrees, 23 minutes, 29 seconds West.

RANGE IN CHARACTERISTICS:

Average annual soil temperature - 44 to 46 degrees F.
Average summer soil temperature - 52 to 55 degrees F. with an O horizon
Moisture control section - dry 45 to 60 days (August to September), moist October through July.
Depth to bedrock - more than 60 inches.
Clay content - 3 to 8 percent in particle-size control section.
Umbric epipedon - 7 to 12 inches thick.
Surface stones - 0.1 to 15 percent.

Volcanic ash influence- 7 to 12 inches thick.
Volcanic glass content - 5 to 20 percent.
Acid-oxalate extr. Al + 1/2 Fe - 0.4 to 1.0 percent.
Phosphate retention - 25 to 55 percent.

A horizon
Value - 4 or 5 dry, 2 or 3 moist
Chroma - 1 to 3 dry or moist
Texture - ASHY-GR-VFSL, ASHY-GR-L, ASHY-GR-FSL
Clay content - 3 to 10 percent
Gravel content - 15 to 25 percent
Cobble content - 0 to 5 percent
Stone content - 0 to 5 percent
Bulk density - 1.00 to 1.20 g/cc
Mica content - 2 to 20 percent
Reaction - slightly acid to neutral

AB horizon
Value - 4 or 5 dry
Chroma - 2 or 3 dry or moist
Texture - ASHY-CBV-VFSL, ASHY-GRV-L, ASHY-GRV-FSL, ASHY-CBV-L
Clay content - 3 to 10 percent
Gravel content - 15 to 30 percent
Cobble content - 15 to 25 percent
Stone content - 0 to 5 percent
Bulk density - 1.00 to 1.20 g/cc
Mica content - 2 to 20 percent
Reaction - strongly acid to slightly acid

Bw horizon
Hue - 10YR or 2.5Y
Value - 5 or 6 dry, 3 or 4 moist
Chroma - 3 or 4 dry or moist
Texture - ASHY-CBV-VFSL, ASHY-CBV-L, ASHY-GRV-L, ASHY-GRV-FSL
Clay content - 3 to 10 percent
Gravel content - 20 to 40 percent
Cobble content - 15 to 30 percent
Stone content - 5 to 15 percent
Mica content - 2 to 20 percent
Reaction - strongly acid to slightly acid

C horizons
Hue - 10YR or 2.5Y
Value - 5 to 7 dry, 3 to 5 moist
Chroma - 3 or 4 dry or moist
Texture - GRV-VFSL, CBV-VFSL, CBX-FSL, CBV-FSL, STV-FSL, STX-FSL
Clay content - 3 to 8 percent
Gravel content - 15 to 30 percent
Cobble content - 20 to 35 percent
Stone content - 5 to 40 percent
Mica content - 25 to 35 percent
Reaction - strongly acid to slightly acid

COMPETING SERIES: There are no competing series.

GEOGRAPHIC SETTING: McArthur soils are on south and west-facing mountain slopes and breaklands. Slopes range from 35 to 85 percent. They formed in residuum derived from schist, gneiss, and granite bedrock with minor amounts of volcanic ash in the surface layers. Elevations range from 1,800 to 4,800 feet. The average annual air temperature is 44 to 46 degrees F. and average annual precipitation is 25 to 45 inches. The average frost-free period is 90 to 120 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Highfalls (T), Idamont, Katka (T), Pearsoncreek (T), Jaypeak (T), and Treble series. Highfalls soils are on mountains and foothills and formed in glacial till and are ashy over loamy-skeletal. Idamont soils are on mountains and foothills and formed in glacial till and are ashy over loamy. Katka soils are on south-facing mountain slopes at higher elevations and are cryic. Pearsoncreek and Treble soils are on mountains and foothills and formed in glacial till and do not have an umbric epipedon. Jaypeak soils are on north-facing mountain slopes and are ashy over loamy-skeletal.

DRAINAGE AND PERMEABILITY: Well drained; rapid to very rapid runoff; moderately rapid permeability.

USE AND VEGETATION: These soils are used for timber production, wildlife habitat, recreation, and watershed. Potential natural vegetation is mainly Douglas-fir, ponderosa pine, and lodgepole pine with an understory of Saskatoon serviceberry, pine reedgrass, mallow ninebark, creambush oceanspray, common snowberry, low Oregongrape, myrtle pachystima, white spirea, Rocky Mountain maple, baldhip rose, Columbia brome, strawberry, and starry false Solomons seal.

DISTRIBUTION AND EXTENT: Northern Idaho, and possibly northwestern Montana and northeastern Washington. This series is not extensive

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

SERIES ESTABLISHED: Boundary County, Idaho, 2002.

REMARKS:

Diagnostic horizons and features recognized in this pedon are:

Umbric epipedon - the zone from 2 to 9 inches (A and AB horizons)

Cambic horizon - the zone from 9 to 17 inches (Bw horizon)

Particle-size control section - the zone from 10 to 40 inches (part of the Bw, the C1, and part of the C2 horizon)

The mineralogy class was changed from paramicaceous to micaceous in 07/2010 by the National Soil Survey Center on request of the responsible MLRA regional office. The change was necessary based on the eleventh edition of the Keys to Soil Taxonomy, 2010.

The 11/2010 revision reflects a reclassification from Dystroxerepts to Humixerepts greatgroup based on revisions to the 11th Edition Keys to Soil Taxonomy. No other changes were made during this revision.

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National Cooperative Soil Survey
U.S.A.