LOCATION TOHOBIT IDEstablished Series
TAXONOMIC CLASS: Sandy-skeletal, mixed, frigid Aeric Calciaquolls
TYPICAL PEDON: Tohobit silt loam--on a 2 percent slope at 4,650 feet with grass and willow vegetation. (Colors are for dry soil unless otherwise noted. When described on August 6, 1987, the soil was dry to 19 inches, moist from 19 to 55 inches and wet below 55 inches.)
Ak1--0 to 3 inches; dark grayish brown (10YR 4/2) silt loam, very dark brown (10YR 2/2) moist; moderate fine subangular blocky structure; slightly hard, friable, nonsticky and nonplastic; many very fine and few fine, medium coarse and very coarse roots; many very fine and fine irregular pores; strongly effervescent (17 percent calcium carbonate equivalent); moderately alkaline (pH 8.0); abrupt wavy boundary.
Ak2--3 to 9 inches; dark grayish brown (10YR 4/2) silt loam, very dark brown (10YR 2/2) moist; moderate fine and medium subangular blocky structure; slightly hard, very friable, nonsticky and slightly plastic; many very fine and few fine, medium, coarse and very coarse roots, many very fine and fine irregular pores; strongly effervescent (17 percent calcium carbonate equivalent); moderately alkaline (pH 8.0); clear wavy boundary. (combined thickness of the Ak horizons is 8 to 12 inches)
Bw1--9 to 16 inches; grayish brown (10YR 5/2) silt loam, brown (10YR 4/3) moist; weak medium and coarse subangular blocky structure; slightly hard, friable, nonsticky and slightly plastic; many very fine and few fine, medium, coarse and very coarse roots, many very fine and fine irregular pores; slightly alkaline (pH 7.4); clear wavy boundary.
Bw2--16 to 21 inches; brown (10YR 5/3) fine sandy loam, brown (10YR 4/3) moist; few fine faint yellowish brown (10YR 5/4) redox concentrations; weak medium and coarse subangular blocky structure; soft, very friable, nonsticky and nonplastic; common very fine and few fine and medium roots; many very fine and fine irregular pores; 10 percent gravel; slightly alkaline (pH 7.4); gradual wavy boundary. (combined thickness of the Bw horizons is 4 to 13 inches)
2Cg1--21 to 45 inches; multicolored extremely gravelly coarse sand; many fine and medium distinct strong reddish yellow (7.5YR 6/6) redox concentrations on coarse fragments; single grain; loose; common very fine and few fine and medium roots; many fine and medium irregular pores; 75 percent gravel, 15 percent cobbles; slightly alkaline (pH 7.5); clear wavy boundary. (20 to 30 inches thick)
2Cg2--45 to 49 inches; multicolored extremely gravelly coarse sand; many medium and coarse distinct strong reddish yellow (7.5YR 6/6) redox concentrations on coarse fragments; single grain; loose; few very fine roots; many fine and medium irregular pores; 60 percent gravel, 10 percent cobbles; slightly alkaline (pH 7.5); clear wavy boundary. (2 to 6 inches thick)
2Cg3--49 to 55 inches; multicolored sand; many fine and medium distinct reddish yellow (5YR 6/8) redox concentrations; single grain; loose; few very fine roots; many fine irregular pores; 10 percent gravel; slightly alkaline (pH 7.5); clear wavy boundary. (0 to 8 inches thick)
2Cg4--55 to 60 inches; light brownish gray (10YR 6/2) loamy fine sand, very dark grayish brown (10YR 3/2) moist; many fine and medium distinct strong brown (7.5YR 5/6) redox concentrations; weak medium and coarse subangular blocky structure; soft, very friable, nonsticky and nonplastic; few very fine roots; many fine irregular pores; 10 percent gravel; slightly alkaline (pH 7.5).
TYPE LOCATION: Lemhi County, Idaho: about 1 mile north of Ellis, Idaho, about 100 feet south and 100 feet west of the northeast corner of section 24, T.16N, R.20E.
RANGE IN CHARACTERISTICS:
Average annual soil temperature - 45 to 47 degrees F
Mollic epipedon thickness - 8 to 12 inches
Thickness of calcic horizon - 8 to 12 inches
Depth to sand and gravel (2C horizon) - 12 to 24 inches
Depth to high water table - 1.5 to 3.0 feet March to October
Control section average - Percent clay: 2 to 10 percent
Coarse fragments - 40 to 80 percent (control section average)
Ak horizon
value - 4 or 5 dry, 2 or 3 moist
chroma - 1 through 3 dry or moist
calcium carbonate equivalent - 15 to 20 percent
reaction - slightly or moderately alkaline
Bw horizon
value - 5 or 6 dry, 3 or 4 moist
chroma - 2 or 3 dry or moist
texture - SIL, FSL, GR-SIL
coarse fragments - 0 to 30 percent
2Cg horizon
texture - (upper part) GRX-COS, GRX-S, GRV-COS
(lower part) GRX-COS, GRX-S, GRV-COS, S, LFS
coarse fragments - 10 to 90 percent
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING: Tohobit soils are on valley flats at elevations of 3,600 to 5,000 feet. The soils formed in alluvium. Slopes range from 0 to 3 percent. The climate is cold and moist in winter and spring and dry in summer. Average annual precipitation is 8 to 14 inches. Average annual air temperature is 38 to 47 degrees F. The frost-free period is 60 to 90 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Bartonflat, Bromaglin, Bursteadt, Dawtonia, and Zer soils. Bartonflat and Bromaglin soils are on terraces and fan terraces. Bartonflat soils have sand and gravel at 3 to 12 inches and lack a water table. Bromaglin soils are noncalcareous to below 7 inches and lack a water table. Bursteadt soils are on valley flats and have coarse-loamy particle-size control sections. Dawtonia soils are on fan terraces, lack mollic epipedons and have argillic horizons. Zer soils are on fan terraces, are well drained and have loamy-skeletal particle-size control sections.
DRAINAGE AND PERMEABILITY: Somewhat poorly drained. Slow runoff. Moderate permeability in the upper part and very rapid permeability below. Occasional flooding for brief periods April to June. Water table at 1.5 to 3.0 feet March to October.
USE AND VEGETATION: Pastureland and wildlife habitat. The native vegetation is willows, wheatgrass, basin wildrye, and sedges.
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:
Mollic epipedon - The zone from the soil surface to 9 inches (Ak1 and Ak2 horizons).
Calcic horizon - The zone from the soil surface to 9 inches (Ak1 and Ak2 horizons).
Cambic horizon - the zone from 9 to 21 inches (Bw1 and Bw2 horizons). Particle-size control section - The zone from 10 to 40 inches (part of the Bw1, the Bw2 and part of the 2Cg1 horizons).