LOCATION PERREAU IDEstablished Series
TAXONOMIC CLASS: Fine-loamy, mixed, superactive, frigid Xeric Calciargids
TYPICAL PEDON: Perreau silt loam--on a 7 percent south-facing slope at 4,600 feet elevation in rangeland. (Colors are for dry soil unless otherwise noted. When described on August 24, 1988, the soil was dry throughout).
A1--0 to 5 inches; light yellowish brown (10YR 6/4) loam, dark yellowish brown (10YR 4/4) moist; weak thin platy structure; soft, very friable, nonsticky and slightly plastic; many very fine and fine roots; many very fine and fine irregular pores; 10 percent gravel; slightly alkaline (pH 7.4); abrupt smooth boundary.
A2--5 to 8 inches; light yellowish brown (10YR 6/4) gravelly loam, dark yellowish brown (10YR 4/4) moist; moderate fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine and fine roots; many very fine and fine irregular pores; 15 percent gravel; slightly alkaline (pH 7.4); clear smooth boundary. (Combined thickness of the A horizons is 4 to 12 inches)
Bt--8 to 18 inches; brown (7.5YR 5/4) gravelly clay loam, brown (7.5YR 4/4) moist; moderate fine and medium prismatic structure; hard, firm, moderately sticky and moderately plastic; many very fine and fine roots; many very fine and fine tubular pores; many prominent clay films on faces of peds; 15 percent gravel; moderately alkaline (pH 8.2); clear wavy boundary. (8 to 14 inches thick)
Bkz1--18 to 21 inches; yellowish brown (10YR 5/4) gravelly loam, dark yellowish brown (10YR 4/4) moist; hard, firm, slightly sticky and slightly plastic; few very fine and fine roots; many very fine and fine tubular pores; 15 percent gravel; many distinct calcium carbonate coatings on coarse fragments; common calcium carbonate filaments and salt crystals; 15 percent weakly cemented cicada nodules; violently effervescent; moderately alkaline (pH 8.1); clear wavy boundary.
Bkz2--21 to 27 inches; pale brown (10YR 6/3) very gravelly silt loam, brown (10YR 4/3) moist; moderate fine prismatic structure parting to moderate thin platy; slightly hard, friable, slightly sticky and slightly plastic; few very fine and fine roots; many very fine and fine irregular pores; 30 percent gravel; prominent calcium carbonate coatings on all sides of coarse fragments; common calcium carbonate filaments and salt crystals; 15 percent weakly cemented cicada nodules; violently effervescent; moderately alkaline (pH 7.9); clear wavy boundary.
Bkz3--27 to 37 inches; light yellowish brown (10YR 6/4) very gravelly loam, brown (10YR 4/3) moist; moderate medium angular blocky structure; slightly hard, friable, slightly sticky and plastic; few very fine roots; many very fine and fine irregular pores; 45 percent gravel; prominent calcium carbonate coatings on all sides of coarse fragments; salt crystals present in horizon; 10 percent weakly cemented cicada nodules; strongly effervescent; slightly alkaline (pH 7.8); clear wavy boundary. (Combined thickness of the Bkz horizons is 12 to 36 inches)
Bk1--37 to 51 inches; light yellowish brown (10YR 6/4) very gravelly loam, brown (7.5YR 5/4) moist; weak fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine and fine irregular pores; 60 percent gravel; prominent calcium carbonate coatings on all sides of coarse fragments; strongly effervescent; slightly alkaline (pH 7.6); gradual wavy boundary. (8 to 20 inches thick)
Bk2--51 to 60 inches; very pale brown (10YR 7/4) very gravelly sandy loam, brown (7.5YR 5/4) moist; single grain; loose; many very fine and fine irregular pores; 40 percent gravel, 15 percent cobbles; prominent calcium carbonate coatings on all sides of coarse fragments; strongly effervescent; slightly alkaline (pH 7.6).
TYPE LOCATION: Lemhi County, Idaho; about 3 miles north of Baker, Idaho; about 1,050 feet south and 1,585 feet east of the northwest corner of section 22, T. 21 N., R. 23 E. Latitude - 45 degrees, 09 minutes, 17 seconds North; Longitude - 113 degrees, 43 minutes, 23 seconds West.
RANGE IN CHARACTERISTICS:
Average annual soil temperature - 43 to 47 degrees F.
Control section; percent clay - 18 to 30
Depth to calcic horizon - 12 to 26 inches
Depth to top of argillic - 3 to 12 inches
A horizon
Value - 5 or 6 dry, 3 or 4 moist
Chroma - 2 through 4 dry or moist
Bt horizon
Hue - 7.5YR or 10YR
Value - 5 or 6 dry, 4 or 5 moist
Chroma - 2 through 4 dry or moist
Texture - GR-CL, GR-L, GR-SICL
Coarse fragments - 15 to 35 percent
Bkz horizon
Value - 5 or 6 dry, 4 or 5 moist
Chroma - 3 or 4 dry or moist
Texture - GR-CL, GR-SICL, GR-L, GRV-L, GR-SIL
Coarse fragments - 15 to 50 percent
Bk horizons
Hue - 7.5YR or 10YR
Value - 6 through 8 dry and 5 or 6 moist
Texture - GRX-L, GRV-SL, GRV-L
Rock fragments - 45 to 70 percent
COMPETING SERIES: These are the Credo, Favret, and Pedoli soils. Credo soils are 14 to 20 inches deep to the top of the argillic horizon and have silica cementation immediately below the argillic. Favret soils are moderately deep to argillite bedrock. Pedoli soils have concentrations of silica and lack concentrations of salt immediately below the argillic horizon.
GEOGRAPHIC SETTING: Perreau soils are on dissected stream terraces and foothills and have slopes of 1 to 45 percent. Elevations range from 4,000 to 6,000 feet. The soils formed in lacustrine sediments and alluvium from mixed sources. The climate is cold and moist in winter and spring, and dry in summer. Average annual precipitation is 7 to 12 inches. Average summer temperature is 65 to 70 degrees F. Average annual temperature is 38 to 46 degrees F. and frost-free period is 70 to 100 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Dawtonia, Millhi, Packham, Pattee, Snowslide and Venum soils. Dawtonia soils are on foothills and have loamy-skeletal particle-size control sections. Millhi soils are on foothills and have fine particle-size control sections and natric horizons. Packham soils are on fan terraces and have loamy-skeletal particle-size control sections. Pattee soils are on terraces and foothills and have coarse-loamy particle-size control sections. Snowslide soils are on fan terraces and have loamy-skeletal particle-size control sections. Venum soils are on foothills and mountains and have clayey-skeletal particle-size control sections.
DRAINAGE AND PERMEABILITY: Well drained; slow and medium runoff; moderately slow permeability.
USE AND VEGETATION: Rangeland. Vegetation is mainly Wyoming big sagebrush and bluebunch wheatgrass.
DISTRIBUTION AND EXTENT: East-central Idaho. These soils are not extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Lemhi County, Idaho, 1999.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - the zone from 0 to 8 inches (The A1 and A2 horizons).
Argillic horizon - the zone from 8 to 18 inches (Bt horizon).
Calcic horizon - the zone from 18 to 27 inches (the Bkz1 and Bkz2 horizons).
Particle-size control section - the argillic horizon or the zone from 8 to 18 inches (Bt horizon).
ADDITIONAL DATA: S91ID-59-001