LOCATION TOPONCE IDEstablished Series
TAXONOMIC CLASS: Fine, smectitic Vertic Argicryolls
TYPICAL PEDON: Toponce silt loam - on a 22 percent southwest facing slope under aspen at 6,400 feet elevation. (Colors are for air-dry soil unless otherwise noted. When described the soil was moist from 0 to 3 inches, dry from 3 to 28 inches, and moist from 28 to 60 inches.)
A--0 to 3 inches; dark grayish brown (10YR 4/2) silt loam, very dark brown (10YR 2/2) moist; moderate fine granular structure; soft, friable, slightly sticky and slightly plastic; many very fine and fine roots; many very fine interstitial pores; about 10 percent gravel, slightly acid (pH 6.3); clear smooth boundary. (2 to 5 inches thick)
AB--3 to 14 inches; dark grayish brown (10YR 4/2) silty clay loam, very dark brown (10YR 2/2) moist; strong medium, fine, and very fine subangular blocky structure; hard, firm, moderately sticky and moderately plastic; many very fine and fine and few medium roots; many very fine tubular and interstitial pores; about 5 percent gravel; slightly acid (pH 6.3); clear smooth boundary. (0 to 13 inches thick)
Bt1--14 to 21 inches; brown (10YR 4/3) silty clay loam, very dark grayish brown (10YR 3/2) moist; strong fine and very fine subangular blocky structure; hard, firm, moderately sticky and moderately plastic; common very fine and fine and few medium roots; common very fine tubular and few interstitial pores; few faint clay films in pores and on faces of peds; about 5 percent rock fragments, mostly gravel; moderately acid (pH 5.8); clear smooth boundary. (0 to 12 inches thick)
Bt2--21 to 28 inches; brown (10YR 5/3) silty clay, dark yellowish brown (10YR 4/4) moist; moderate medium prismatic structure parting to strong medium angular blocky; very hard, very firm, moderately sticky and moderately plastic; common very fine and few fine and medium roots; mostly along faces of peds and cracks; common very fine tubular pores; many distinct clay films in pores and on faces of peds; about 5 percent rock fragments, mostly gravel; moderately acid (pH 5.8); clear smooth boundary. (6 to 10 inches thick)
Bt3--28 to 60 inches; brown (10YR 5/3) clay, dark yellowish brown (10YR 4/4) moist; moderate coarse prismatic structure; extremely hard, extremely firm, very sticky and very plastic; few very fine, fine, and medium roots along faces of peds and cracks; common very fine tubular pores; many distinct clay films in pores and on faces of peds; about 2 percent rock fragments; mostly gravel; moderately acid (pH 5.9).
TYPE LOCATION: Bannock County, Idaho; about 1/4 mile southeast of the convergence of Shingle Creek and Spring Creek; 2,450 feet east and 300 feet north of the southwest corner of sec. 29, T. 11 S., R. 39 E.
RANGE IN CHARACTERISTICS:
Moisture regime - udic
Depth of mollic epipedon - 18 to 25 inches
Average annual soil temperature - 38 to 43 degrees F
Solum thickness - 60 inches or more
A horizon
Color value, dry - 4 or 5
Value, moist - 2 or 3
Chroma, dry or moist - 1 through 3
Reaction - moderately acid to slightly acid
Bt horizon
Color value, dry - 4 through 6
Value, moist - 2 through 5
Chroma, dry or moist - 2 through 4
Clay - 35 to 55 percent
Texture - silty clay loam, silty clay, clay
Rock fragments - 0 to 5 percent
Reaction - moderately acid to slightly acid
COMPETING SERIES:
Beaverdam (ID) - have a mollic epipedon less than 16 inches thick.
Buckskin (ID+WY) - are neutral or slightly alkaline in the subsoil.
Cimarron (CO+WY) - have a mollic epipedon less than 16 inches thick.
Cucharas (CO) - have a mollic epipedon less than 16 inches thick.
Gillum (SD+WY) have a glossic horizon.
Gourley (CO) - have a mollic epipedon less than 16 inches thick.
Hairpin (MT) - have an ustic moisture regime.
Heathcoat (ID+CO) - have a mollic epipedon less than 16 inches thick.
Helmet (CO) - have a mollic epipedon less than 16 inches thick.
Savar (WY) - have a horizon with secondary carbonate accumulation.
Slights (ID) - have a xeric moisture regime.
Sudworth (CO+ID) - have a lithologic discontinuity.
Sudpeak (ID) - have a seasonally high water table at a depth of 3 to 6 feet.
Wetopa (CO) - do not have a BC or C horizon within 60 inches.
Youman (CO) - have a mollic epipedon less than 16 inches thick.
GEOGRAPHIC SETTING: Toponce soils are on foothills, mountain slopes, and fan terraces at elevations of 5,500 to 7,100 feet. Slopes range from 4 to 40 percent. These soils formed in colluvium from sedimentary and metasedimentary rocks, predominantly sandstone and quartzite. Average annual precipitation ranges from 20 to 28 inches. Average annual temperature ranges from 37 to 41 degrees F. Frost-free season is about 40 to 70 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Beaverdam, Broadhead, Hades, Harkness, Pavohroo, Sedgway, and Yago soils. Broadhead soils are frigid. Hades and Pavohroo soils are fine-loamy. Harkness soils lack a mollic epipedon. Sedgway and Yago soils are skeletal. Beaverdam, Harkness, Pavohroo, and Sedgway soils are at slightly higher elevations than Toponce and are on north- and east-facing mountain slopes. Broadhead, Hades, and Yago soils are on similar landscape positions but are on south- and west-facing slopes.
DRAINAGE AND PERMEABILITY: Well drained; runoff is medium to very rapid; permeability is slow.
USE AND VEGETATION: These soils are used mainly for grazing, wildlife habitat, and watershed. Important native plants are quaking aspen, sticky geranium, common snowberry, and pine reedgrass.
DISTRIBUTION AND EXTENT: These soils are inextensive in southeastern Idaho. MLRA 13 and 43B.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Bannock County, Idaho, 1983.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon: from the soil surface to 21 inches (A, AB and Bt1 horizons);
Argillic horizon: from 14 to 60 inches (Bt1, Bt2 and Bt3 horizons);
Particle size control section: from 14 to 34 inches (Bt1, Bt2 and part of the Bt3 horizons).
Toponce soils have a cryic soil temperature regime and an udic moisture regime.