LOCATION THOMASFORK IDEstablished Series
TAXONOMIC CLASS: Fine, smectitic, frigid Fluvaquentic Vertic Endoaquolls
TYPICAL PEDON: Thomasfork silty clay loam, irrigated barley. When described on July 2, 1991, the soil was dry to 10 inches and moist below. (Colors are for dry soil unless otherwise noted.)
Ap1--0 to 2 inches; dark gray (10YR 4/1) silty clay loam, black (10YR 2/1) moist; strong fine granular structure; hard, very friable, moderately sticky and moderately plastic; common very fine and few medium roots; many very fine irregular pores; cracks 0.5 to 1 inch wide, 12 to 18 inches apart; strongly effervescent disseminated lime; slightly alkaline (pH 7.7); abrupt smooth boundary.
Ap2--2 to 10 inches; dark gray (10YR 4/1) silty clay loam, black (10YR 2/1) moist; strong very coarse prismatic structure parting to fine and medium subangular blocky; hard, very friable, moderately sticky and moderately plastic; common very fine roots; many very fine irregular and tubular pores; cracks 0.5 to 1 inch wide, 12 to 18 inches apart; strongly effervescent; disseminated lime; neutral (pH 7.1); abrupt smooth boundary. (Combined thickness of the Ap horizon is 2 to 18 inches.)
AB--10 to 16 inches; 70 percent dark gray (10YR 4/1) and 30 percent grayish brown (10YR 5/2) silty clay loam, very dark gray (10YR 3/1) moist, few fine prominent dark brown (7.5YR 3/4) moist redox concentrations; moderate medium and coarse subangular blocky structure parting to strong fine and medium granular; hard, friable, moderately sticky and moderately plastic; common very fine roots; many very fine tubular pores; cracks 0.5 to 1 inch wide, 12 to 18 inches apart; slightly effervescent; disseminated lime; slightly alkaline (pH 7.8); clear wavy boundary. (6 to 13 inches thick)
Bg1--16 to 21 inches; 55 percent dark gray (10YR 4/1) and 45 percent pale brown (10YR 6/3) silty clay loam, very dark grayish brown (10YR 3/2) moist, few fine prominent dark brown (7.5YR 3/4) redox concentrations and common fine and medium prominent black (N 2/) moist redox depletions; moderate medium and coarse subangular blocky structure; hard, very friable, moderately sticky and moderately plastic; common very fine and few fine roots; many very fine and few fine and medium tubular pores; cracks 0.5 to 1 inch wide, 12 to 18 inches apart; strongly effervescent; disseminated lime; slightly alkaline (pH 7.8); gradual wavy boundary. (4 to 21 inches thick)
Bg2--21 to 28 inches; pale brown (10YR 6/3) silty clay loam, dark brown (10YR 3/3) moist, common fine distinct dark brown (7.5YR 3/4) redox concentrations and common fine and medium prominent black (N 2/) moist redox depletions; moderate medium and coarse subangular blocky structure; hard, very friable, moderately sticky and moderately plastic; common very fine and fine roots; many very fine and few fine and medium tubular pores; violently effervescent; disseminated lime; slightly alkaline (pH 7.8); gradual wavy boundary. (5 to 10 inches thick)
2Agb--28 to 35 inches; very dark grayish brown (10YR 3/2) silty clay loam, black (N 2/) moist, common fine distinct brown (7.5YR 4/3) moist redox concentrtions; moderate medium and coarse subangular blocky structure parting to weak fine granular; hard, very friable, moderately sticky and very plastic; common very fine roots; common very fine and fine tubular pores; slightly alkaline (pH 7.6); gradual wavy boundary. (0 to 7 inches thick)
2Btgb--35 to 48 inches; gray (10YR 5/1) silty clay, dark gray (10YR 4/1) moist, many fine and medium prominent dark brown (7.5YR 3/4) moist redox concentrations; moderate medium and coarse subangular blocky structure parting to strong fine angular blocky; very hard, friable, moderately sticky and very plastic; common very fine tubular pores; slightly alkaline (pH 7.7); clear wavy boundary. (0 to 13 inches thick)
3C--48 to 60 inches; pale brown (10YR 6/3) very fine sandy loam, dark grayish brown (10YR 4/2) moist; massive; hard, friable, slightly sticky and slightly plastic; common very fine and few fine tubular pores; slightly alkaline (pH 7.8).
TYPE LOCATION: Bear Lake County, Idaho; about 1.5 miles north of Geneva, Idaho; about 900 feet north and 1300 feet west of the southeast corner of section 10, T. 12 S., R. 46 E.; USGS Giraffe Creek 7.5 minute topographic quadrangle; 42 degrees 23 minutes 22 seconds north latitude and 111 degrees 03 minutes 32 seconds west longitude, NAD 27.
RANGE IN CHARACTERISTICS:
Thickness of mollic epipedon - 21 to 52 inches
Average annual soil temperature - 41 to 44 degrees F.
Depth to redox features - 10 to 20 inches
Depth to seasonal high water table - 10 to 20 inches December through May
Particle-size control section
Clay content - averages 35 to 50 percent
Present in some pedons
O horizons
A horizons
Hue - 10YR or 7.5YR
Value - 3 to 5 dry, 2 or 3 moist
Chroma - 1 or 2 dry or moist
Reaction - neutral or slightly alkaline
AB and B horizons
Hue - 10YR, 7.5YR, 2.5Y or 5Y
Value - 4 to 7 dry, N2 to 4 moist
Chroma - 1 through 3 dry and 0 to 3 moist
Texture - SICL, SIC, or C
Reaction - slightly or moderately alkaline
2Agb and 2Btgb horizons
Hue - 10YR or 7.5YR
Value - 3 to 6 dry, N2 to 4 moist
Chroma - 1 or 2 dry and 0 to 2 moist
Texture - SICL, SIC, or C
Reaction - slightly or moderately alkaline
3C horizons
Hue - 10YR or 7.5YR
Value - 6 or 7 dry, 3 or 4 moist
Chroma - 2 or 3 dry or moist
Texture - VFSL, L and GR-SIL
Reaction - slightly or moderately alkaline
COMPETING SERIES:
Mountmed (CA) - mollic epipedon is less than 21 inches thick.
GEOGRAPHIC SETTING: Thomasfork soils are on low stream terraces and flood plains. They have slopes of 0 to 2 percent. They formed in fine textured alluvium. The average annual precipitation ranges from 12 to 18 inches, and the average annual temperature ranges from 39 to 43 degrees F. The frost-free period is about 70 to 90 days. Elevations are 5,800 to 6,400 feet.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Bear Lake, Bern (T) and Raynal (T) series. Bear Lake soils are poorly drained, have mollic epipedons less than 20 inches thick and have fine-silty particle-size control sections. Bern soils are moderately well drained and have fine-silty particle-size control sections. Raynal soils have a fine-silty particle-size control section. Bear Lake soils are on floodplains on positions below Thomasfork soils. Bern soils are on stream terraces above Thomasfork soils. Raynal soils are on similar positions to Thomasfork soils but are located to the sides of Thomasfork.
DRAINAGE AND PERMEABILITY: Poorly drained; slow permeability; occasional or rare flooding for brief periods December through May.
USE AND VEGETATION: These soils are used mainly for small grains and hayland.
DISTRIBUTION AND EXTENT: This soil is of small extent in southeastern Idaho. MLRA 13.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Bear Lake County, Idaho, 2008.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - the zone from the soil surface to 21 inches (the Ap1, Ap2, AB and Bg1 horizons).
Fluvaquentic feature - irregular decrease in organic carbon content at 10 to 50 inches.
Vertic feature - Cracks 0.37 to 1 inch wide extending from the surface or base of the Ap horizon to 20 inches from July to December and a linear extensibility greater than 6.0 cm between the soil surface and 40 inches.
Aquic moisture regime.
Particle-size control section - the zone from 10 inches to 40 inches (the AB, Bg1, Bg2, 2Agb and part of the 2Btgb horizons)