LOCATION IDAMONT ID+MTEstablished Series
TAXONOMIC CLASS: Ashy over loamy, glassy over mixed, superactive, frigid Alfic Udivitrands
TYPICAL PEDON: Idamont ashy silt loam, forested; on a south-facing slope of 25 percent at 2,800 feet elevation. When described on November 13, 1972, the soil was moist. Pedon was redescribed on August 16, 1994. (Colors are for dry soil unless otherwise stated.)
Oi--0 to 1 inch; needles and twigs. (0.5 to 2 inches thick)
Oe-1 to 3 inches; partly decomposed needles and twigs mixed with Mt. St. Helens volcanic ash. (0.5 to 2 inches thick)
A--3 to 4 inches; grayish brown (10YR 5/2) ashy silt loam, very dark grayish brown (10YR 3/2) moist; moderate fine granular structure; soft, very friable, slightly sticky and slightly plastic; many fine and medium roots; many very fine pores; slightly acid (pH 6.4); abrupt wavy boundary. (1 to 2 inches thick)
Bw1--4 to 10 inches; light yellowish brown (10YR 6/4) ashy silt loam, dark yellowish brown (10YR 4/4) moist; moderate fine granular structure; soft, very friable, slightly sticky and slightly plastic; many fine and medium roots; many very fine pores; slightly acid (pH 6.4); clear wavy boundary. (5 to 8 inches thick)
Bw2--10 to 21 inches; light yellowish brown (10YR 6/4) ashy silt loam, dark yellowish brown (10YR 4/4) moist; weak medium subangular blocky structure; soft, very friable, slightly sticky and slightly plastic; many fine and medium roots; many very fine and fine pores; slightly acid (pH 6.2); clear wavy boundary. (7 to 13 inches thick)
2Bw3--21 to 31 inches; very pale brown (10YR 7/4) gravelly loam, yellowish brown (10YR 5/4) moist; weak medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine, fine and medium roots; many very fine and fine pores; 15 percent gravel; slightly acid (pH 6.4); clear wavy boundary. (8 to 12 inches thick)
2Bt--31 to 55 inches; pale brown (10YR 6/3) gravelly sandy loam, brown (10YR 4/3) moist; weak coarse subangular blocky structure; hard, friable, slightly sticky and slightly plastic; few fine roots; many fine and medium pores; few faint clay films on faces of peds and lining pores; many thin yellowish brown (10YR 5/4) lamellae; 25 percent gravel; slightly acid (pH 6.4); gradual wavy boundary. (18 to 24 inches thick)
3C--55 to 60 inches; light gray (10YR 7/2) extremely cobbly sandy loam, grayish brown (10YR 5/2) moist; massive; slightly hard, friable, nonsticky and nonplastic; 50 percent gravel, 20 percent cobbles, and 10 percent stones; slightly acid (pH 6.4).
TYPE LOCATION: Boundary County, Idaho; Twentymile Peak Road southeast of Naples; about 1,000 feet north and 900 feet east of the southwest corner of section 16, T. 60 N., R. 1 E. Latitude - 48 degrees, 32 minutes, 51 seconds North; Longitude - 116 degrees, 20 minutes, 54 seconds West; USGS Quadrangle - Twentymile Creek.
RANGE IN CHARACTERISTICS:
Average annual soil temperature - 43 to 46 degrees F.
Average summer soil temperature - 49 to 53 degrees F. with an O horizon.
Solum thickness - 40 to 60 inches
Clay content - 3 to 8 percent in the particle-size control section
Volcanic ash mantle - 14 to 20 inches thick
Volcanic glass content - 30 to 65 percent
Acid-Oxalate extractable Al + 1/2 Fe - 1.0 to 3.0 percent
Phosphate retention - 55 to 90 percent
15 bar water (air dried) - 7 to 12 percent
A horizon
Hue - 10YR or 7.5YR
Value - 4 or 5 dry, 2 or 3 moist
Chroma - 1 to 3 dry or moist
Texture - ASHY-SIL, GR-ASHY-SIL
Clay content - 3 to 8 percent
Rock fragments - 0 to 25 percent
Bulk density - 0.65 to 0.85 g/cc
Reaction - moderately acid to neutral
Bw horizons
Hue - 10YR or 7.5YR
Value - 5 to 7 dry, 3 to 5 moist
Chroma - 4 or 6 dry or moist
Texture - ASHY-SIL, GR-ASHY-SIL, CB-ASHY-SIL in lower part
Clay content - 3 to 8 percent
Rock fragments - 0 to 25 percent
Bulk density - 0.65 to 0.85 g/cc
Reaction - slightly acid to neutral
2Bw horizon (absent in some pedons)
Hue - 10YR or 7.5YR
Value - 6 or 7 dry, 4 or 5 moist
Chroma - 3 or 4 dry or moist
Texture - GR-SL, GR-FSL, GR-L, L, SL, FSL, CB-L, CB-SL
Clay content - 3 to 8 percent
Rock fragments - 0 to 30 percent
Reaction - moderately acid to slightly acid
2Bt horizon
Hue - 10YR or 2.5Y
Value - 6 or 7 dry, 4 or 5 moist
Chroma - 3 or 4 dry or moist
Texture - GR-SL, GR-FSL, GR-L, CB-FSL, CB-L, CB-SL
Clay content - 3 to 8 percent
Rock fragments - 15 to 35 percent
Reaction - moderately acid to slightly acid
3C horizon
Hue - 10YR or 2.5Y
Value - 6 or 7 dry, 4 to 6 moist
Chroma - 2 to 4 dry or moist
Texture - GRV-SL, GRX-SL, CBV-SL, CBX-SL
Clay content - 0 to 5 percent
Rock fragments - 45 to 85 percent
Reaction - moderately acid to slightly acid
COMPETING SERIES: These are the Pend Oreille and Zee series. Pend Oreille soils do not have 2Bw horizons and have less than 50 percent rock fragments in the 2C horizon. Zee soils have 18 to 22 percent clay in the 2Bt horizon.
GEOGRAPHIC SETTING: Idamont soils are on mountains and foothills. Slopes range from 5 to 65 percent. They formed in volcanic ash over glacial till derived from granite, gneiss, and schist. Elevations range from 2,300 to 4,900 feet. The climate is subhumid with cold, snowy winters and warm, relatively dry summers. The average annual air temperature ranges from 43 to 46 degrees F. and the average annual precipitation ranges from 28 to 45 inches. The average frost-free period is 80 to 110 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are Dufort, Kriest, Pend Oreille, and Treble soils. Dufort soils are on southeast and southwest facing mountain slopes, have a xeric moisture regime, and are ashy over loamy-skeletal. Kriest soils are on mountain slopes and have a coarse-loamy control section. Pend Oreille soils are on mountain slopes and have a volcanic ash mantle less than 20 inches thick. Treble soils are on south facing mountain slopes, have a xeric moisture regime and are loamy-skeletal.
DRAINAGE AND PERMEABILITY: Well drained; medium to rapid runoff; moderate permeability in the upper part and moderately rapid below.
USE AND VEGETATION: Woodland, wildlife habitat, and recreation. Natural vegetation is mainly western redcedar, grand fir, western white pine, western larch, and Douglas-fir, with an understory of queencup beadlily, myrtle pachystima, American trailplant, goldthread, sweetscented bedstraw, longtube twinflower, common princespine, and starry false Solomons seal.
DISTRIBUTION AND EXTENT: Northern Idaho, northwestern Montana, and possibly northeastern Washington. This soil is moderately extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Boundary County, Idaho, 1974.
REMARKS:
Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - the zone from the mineral soil surface to 7 inch (A and part of Bw1 horizons)
Cambic horizon - the zone from 4 to 31 inches - (Bw1, Bw2, 2Bw3 horizons)
Argillic horizon - the zone from 31 to 55 inches (2Bt horizon)
Volcanic ash mantle - the zone from 3 to 21 inches (A, Bw1, Bw2 horizons)
Particle-size control section - the zone from the mineral soil surface to 40 inches (A, Bw1, Bw2, 2Bw3, and part of the 2Bt horizon)