LOCATION BENEWAH                 ID

Established Series
Rev. AEK/SHB/JAL
01/2023

BENEWAH SERIES

The Benewah series consists of very deep, moderately well drained soils on foothills and mountain footslopes. They formed in reworked loess and tertiary alluvium with an influence of volcanic ash in the surface. Slope ranges from 5 to 35 percent. The mean annual air temperature is about 44 degrees F., and the mean annual precipitation is about 28 inches.

TAXONOMIC CLASS: Fine-silty, isotic, frigid Vitrandic Haploxeralfs

TYPICAL PEDON: Benewah ashy silt loam, pasture; on a north-facing slope of 12 percent at an elevation of 2,800 feet. Pedon was redescribed on July 26, 2002. (Colors are for dry soil unless otherwise noted.)

Ap--0 to 6 inches; light brownish gray (10YR 6/2) ashy silt loam, dark brown (10YR 3/3) moist; weak fine and medium granular structure; hard, friable, slightly sticky and slightly plastic; many very fine and fine roots; moderately acid (pH 6.0); abrupt wavy boundary. (4 to 7 inches thick)

BE--6 to 15 inches; light yellowish brown (10YR 6/4) ashy silt loam, dark yellowish brown (10YR 4/4) moist; moderate fine subangular blocky structure; very hard, friable, slightly sticky and slightly plastic; common very fine and few fine roots; common very fine and fine tubular pores; common very fine and fine black iron-manganese concretions; 1 percent cobbles; strongly acid (pH 5.5); clear wavy boundary. (3 to 10 inches thick)

E--15 to 18 inches; very pale brown (10YR 7/3) silt loam, brown (10YR 5/3) moist; moderate coarse subangular blocky structure; very hard, friable, moderately sticky and moderately plastic; few very fine and fine roots; common very fine and fine tubular pores; common very fine and fine black iron-manganese concretions; strongly acid (pH 5.1); abrupt wavy boundary. (0 to 6 inches thick)

Bt1--18 to 23 inches; brown (7.5YR 5/4) silty clay loam, brown (7.5YR 4/4) moist; moderate coarse prismatic structure; extremely hard, firm, moderately sticky and moderately plastic; few very fine and fine roots; common very fine and fine tubular pores; many faint, few distinct continuous clay films on faces of peds and in pores; common very fine and fine black iron-manganese concretions; 1 percent fine gravel; 80 percent of ped surfaces are coated with E material; strongly acid (pH 5.4); clear wavy boundary. (5 to 10 inches thick)

Bt2--23 to 34 inches; brown (7.5YR 4/4) silty clay loam, dark reddish brown (5YR 3/4) moist; moderate coarse prismatic structure; extremely hard, very firm, moderately sticky and moderately plastic; few very fine and fine roots; common very fine and fine tubular pores; many faint, common distinct and prominent clay films on faces of peds and in pores; common very fine and fine black iron-manganese concretions; few fine and medium black organic stains; 1 percent fine gravel; 40 percent of ped surfaces are coated with E material; moderately acid (pH 5.7); clear wavy boundary. (9 to 15 inches thick)

Bt3--34 to 60 inches; brown (7.5YR 5/4) silty clay loam, reddish brown (5YR 4/4) moist; moderate coarse prismatic structure; extremely hard, very firm, moderately sticky and moderately plastic; few very fine and fine roots; common very fine and fine tubular pores; many faint, common distinct and prominent clay films on faces of peds and in pores; common very fine, few fine and medium black iron-manganese concretions; very strongly acid (pH 4.5).

TYPE LOCATION: Benewah County, Idaho; about 740 feet north and 540 feet east of the southwest corner of section 24, T.45N., R.4W.; USGS Benewah quadrangle; Latitude 47 degrees, 13 minutes, 23 seconds North; Longitude 116 degrees, 47 minutes, 11 seconds West; NAD 83.

RANGE IN CHARACTERISTICS:

Average annual soil temperature - 43 degrees to 47 degrees F.
Average annual summer soil temperature - 52 degrees to 56 degrees F. with an O horizon
Soil moisture dry 45 to 60 consecutive days from August through September, moist October through July
Depth to bedrock greater than 60 inches
O horizons present in undisturbed pedons 1 to 2 inches thick, mixed with 1980 Mt. St. Helens volcanic ash
Depth to seasonally perched water table 12 to 24 inches February to April

Volcanic ash influence - 7 to 11 inches thick
Moist bulk density - 1.00 to 1.20 g/cc (estimated)
Volcanic glass content - 5 to 20 percent (estimated)
Acid-Oxalate extractable - Al + Fe 0.4 to 1.0 percent (estimated)
Phosphate retention - 25 to 55 percent (estimated)

Ap horizon
Value - 5 or 6 dry, 3 or 4 moist
Chroma - 2 or 3 dry or moist
Clay content -10 to 20 percent
Gravel content - 0 to 5 percent
Reaction - moderately to slightly acid

A horizon (present in some pedons)
Hue -10YR
Value - 5 dry, 3 moist
Chroma - 2 or 3 dry or moist
Texture -Ashy silt loam
Clay content -10 to 20 percent
Gravel content - 0 to 5 percent
Reaction - slightly acid to neutral

BE horizon (this may be a BA horizon in some pedons)
Value - 6 or 7 dry, 4 or 5 moist
Chroma - 3 or 4 dry or moist
Texture - silt loam, Ashy silt loam
Clay content -10 to 20 percent
Gravel content - 0 to 5 percent, fine
Cobble content- 0 to 5 percent
Fe-Mn concretions - none to common
Reaction - strongly acid to slightly acid

E horizon (absent in some pedons)
Clay content -10 to 15 percent
Gravel content - 0 to 5 percent, fine
Cobble content - 0 to 5 percent
Fe-Mn concretions - none to common
Reaction - strongly acid to slightly acid

Bt horizon
Hue - 7.5 YR, 5YR, 10YR
Value - 4 to 6 dry, 3 or 4 moist
Chroma - 3 or 4 dry or moist
Texture - silty clay loam, silt loam
Clay content - 20 to 38 percent (averages less than 35 percent in control section)
Gravel content - 0 to 15 percent (0 to 5 percent fine gravel)
Cobble content - 0 to 5 percent
E material - (skeletans) 0 to 80 percent, 10YR and 2.5Y 7/3 moist
Fe-Mn concretions - none to common
Reaction - very strongly acid to slightly acid

Btx horizon (present in some pedons usually below a depth of 36 inches)
Fragic soil properties - 5 to 15 percent by volume with moist peds having a brittle manner of failure

COMPETING SERIES: There are no competing series. Similar soils are the Arson (T), Longpen and Talmaks series.

Arson soils: mixed mineralogy; 40 to 60 inches to a paralithic contact.; do not have seasonably perched water table at 12 to 24 inches.

Longpen soils: mixed mineralogy; do not have seasonably perched water table at 12 to 24 inches; have 2Btb horizons.

Talmaks soils: mixed mineralogy; do not have a seasonally perched water table at 12 to 24 inches..

GEOGRAPHIC SETTING: Benewah soils are on mountain footslopes and foothills. Slope ranges from 5 to 35 percent. The soils formed in reworked loess and tertiary alluvium with an influence of volcanic ash in the surface. Elevations range from 2,540 to 3,500 feet. The mean annual air temperature is 42 to 46 degrees F. The mean annual precipitation is 25 to 30 inches. The frost-free period is 90 to 120 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Ardenvoir, Porrett, Rasser, Santa, Reggear, Hobnail and Threebear soils. Ardenvoir soils are loamy-skeletal and are on steeper adjacent mountain slopes. Porrett soils have an aquic moisture regime and are in bottomlands and drainageways. Rasser soils are loamy-skeletal and are on similar convex positions. Santa and Reggear soils have a fragipan at depths of 20 to 40 inches and are on adjacent hills. Hobnail and Threebear soils are udic, have thick volcanic ash mantles and are on adjacent hills and dissected terraces.

DRAINAGE AND PERMEABILITY: Moderately well drained; medium to high runoff; permeability is slow. A seasonally perched water table is present at a depth of 12 to 24 inches from February to April.

USE AND VEGETATION: These soils are used for timber production, wildlife habitat, and recreation. Some areas are cleared and used for hay and pasture. Potential natural overstory vegetation is mainly grand fir, western larch, Douglas-fir, ponderosa pine, lodgepole pine, and western white pine with an understory of creambush oceanspray, mallow ninebark, sweetscented bedstraw, white spirea, western meadowrue, hooker fairybells and Idaho goldthread.

DISTRIBUTION AND EXTENT: Northern Idaho, and possibly eastern Washington; MLRA 43. This series is of small extent.

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

SERIES ESTABLISHED: Benewah County, Idaho, 1930.

REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon the zone from 0 to 6 inches (Ap horizon)
Argillic horizon the zone from 18 to 60 inches (Bt1, Bt2, and Bt3 horizons)
Vitrandic feature the zone from 0 to 7 inches (Ap and part of the BE horizon)
Particle-size control section the zone from 18 to 38 inches ((Bt1, Bt2, and part of the Bt3 horizon)
Ultic feature - the zone from 18 to 48 inches having an assumed base saturation (sum) of less than 75 percent in any horizon.

Classification changed in 2002 from Ultic Haploxeralfs fine-silty, mixed, frigid to Vitrandic Haploxeralfs fine-silty, isotic, frigid due to revision in soil taxonomy.

Note: The Benewah series is currently only recognized within the Benewah County, Idaho soil survey. The original concept of the series was that of a soil recognized as having a fragipan. After thorough investigation, this series has been revised to not include a zone within the Bt horizon which meets the definition of a fragipan. In addition, the revised concept includes an influence of mixed ash and loess within the upper part of the soil.

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National Cooperative Soil Survey
U.S.A.