LOCATION SOFTBACK IDEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, frigid Pachic Argixerolls
TYPICAL PEDON: Softback gravelly silt loam, rangeland; on a 55 percent slope, northwest aspect, at 5,000 feet elevation. (When described on September 10, 1993 the soil was dry to 29 inches and slightly moist below. Colors are for air dry soil unless otherwise noted.) Stones on the surface are about 5 to 15 feet apart.
Oi--0 to 1 inch; slightly decomposed plant material composed of maple leaves; abrupt smooth boundary. (0 to 2 inches thick)
A1--1 to 4 inches; very dark gray (10YR 3/1) gravelly silt loam, black (10YR 2/1) moist; strong fine granular structure; soft, very friable, slightly sticky and slightly plastic; many very fine and few fine roots; common very fine irregular and tubular pores; 20 percent gravel; neutral (pH 7.2); clear wavy boundary.
A2--4 to 10 inches; very dark gray (10YR 3/1) gravelly silt loam, black (10YR 2/1) moist; moderate fine and medium subangular blocky structure parting to weak fine granular; soft, very friable, slightly sticky and slightly plastic; common very fine and few fine roots; many very fine and few fine tubular pores; 20 percent gravel; slightly acid (pH 6.2); clear wavy boundary.
A3--10 to 24 inches; very dark gray (10YR 3/1) very cobbly silt loam, black (10YR 2/1) moist; moderate fine and medium subangular blocky structure parting to moderate very fine subangular blocky; soft, very friable, slightly sticky and slightly plastic; common very fine and medium and few fine roots; many very fine and few fine tubular pores; 15 percent gravel, 25 percent cobbles, and 15 percent stones; slightly acid (pH 6.2); clear wavy boundary. (Combined thickness of the A horizons is 20 to 26 inches)
Bt1--24 to 30 inches; brown (7.5YR 5/3) very gravelly silt loam, brown (10YR 4/3) moist; moderate very fine and fine subangular blocky structure; slightly hard, very friable, moderately sticky and moderately plastic; common very fine roots; many very fine and few fine tubular pores; few faint clay films on faces of peds and lining pores; 30 percent gravel and 20 percent cobbles; slightly acid (pH 6.2); clear wavy boundary. (4 to 10 inches thick)
Bt2--30 to 39 inches; brown (7.5YR 5/3) very gravelly clay loam, brown (7.5YR 4/3) moist; moderate fine and medium subangular blocky structure; slightly hard, very friable, moderately sticky and moderately plastic; common very fine and few fine roots; many very fine and few fine tubular and common very fine irregular pores; common distinct clay films on faces of peds and lining pores; 30 percent gravel and 15 percent cobbles; neutral (pH 6.9); gradual wavy boundary. (6 to 14 inches thick)
Bt3--39 to 63 inches; light brown (7.5YR 6/3) extremely gravelly silty clay loam, brown (7.5YR 4/3) moist; moderate medium and coarse subangular blocky structure parting to strong very fine and fine subangular blocky; hard, friable, moderately sticky and very plastic; common very fine and few fine roots; many very fine and few fine tubular and common very fine irregular pores; common distinct clay films on faces of peds and lining pores; 35 percent gravel, 20 percent cobbles, and 15 percent stones; neutral (pH 6.9).
TYPE LOCATION: Franklin County, Idaho; about 1 mile north of the Oneida Narrows Dam; about 1,050 feet south and 1,350 feet east of the northwest corner of section 24, T. 13 S., R. 40 E.; USGS Oneida Narrows Reservoir 7.5 minute topographic quadrangle; 42 degrees, 16 minutes, 55 seconds north latitude and 111 degrees, 44 minutes, 08 seconds west longitude, NAD83.
RANGE IN CHARACTERISTICS:
Profile: (Depths given are measured from the mineral soil surface)
Thickness of mollic epipedon - 20 to 26 inches
Average annual soil temperature - 42 to 46 degrees F.
Particle-size control section:
Clay content average - 25 to 32 percent (total clay)
Rock fragments - 35 to 75 percent
Present in some pedons:
C Horizon
A Horizons:
Hue - 10YR or 7.5YR
Value - 3 through 5 dry, 2 or 3 moist
Chroma - 1 through 3 dry or moist
Reaction - slightly acid or neutral
Bt Horizons:
Hue - 10YR or 7.5YR
Value - 4 through 6 dry, 3 through 5 moist
Chroma - 2 through 6 dry or moist
Texture - GRV-SIL, GRV-CL, GRX-SICL, CBX-SICL, or CBV-CL
Reaction - slightly acid or neutral
COMPETING SERIES: These are the
Bullump,
Bullvaro,
Burchflat,
Camelback,
Chrisflat,
Demner (T),
Dogbed,
Dooh (T),
Erig,
Krenka,
Leroman,
Lockgate,
Murain,
Nutval (T),
Snyderville,
Softscrabble,
Staberg,
Vetagrande, and
Vipont series.Bullump, Burchflat, Demner, Erig, Leroman, Lockgate, Staberg, and Vipont soils are less than 60 inches deep to a lithic or paralithic contact.
Bullvaro and Krenka soils average less than 25 percent clay in the particle-size control section.
Camelback, Chrisflat, Dogbed, Dooh, Murain, Snyderville, Softscrabble, and Vetagrande soils have a mollic epipedon that includes the upper part of the argillic horizon.
Nutval soils have less than 25 percent clay in the particle-size control section.
GEOGRAPHIC SETTING: Softback soils are generally on north-facing mountains and hills. Slopes range from 12 to 65 percent. Elevation ranges from 4,900 to 6,600 feet. The soil formed in colluvium. The average annual precipitation is 16 to 20 inches. The average annual air temperature is 40 to 44 degrees F. The frost-free season is 60 to 90 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Bergquist, Manila, and Yeates Hollow soils. Bergquist soils are on convex slopes above Softback soils. Bergquist soils are deep and have a mollic epipedon less than 20 inches thick. Manila soils are on similar landscape positions as Softback soils, but are generally on slightly higher, convex slopes. Manila soils have a mollic epipedon less than 20 inches thick and have a fine particle-size control section. Yeates Hollow soils are on generally south and west facing concave slopes. Yeates Hollow soils have a mollic epipedon less than 20 inches thick and have a clayey-skeletal particle-size control section.
DRAINAGE AND PERMEABILITY: Well drained; high surface runoff; moderately slow permeability (moderately high saturated hydraulic conductivity).
USE AND VEGETATION: Softback soils are used mainly for rangeland. The potential native vegetation is mainly bigtooth maple and Rocky Mountain juniper with an understory of mountain big sagebrush, common chokecherry, and bluebunch wheatgrass.
DISTRIBUTION AND EXTENT: Southeastern Idaho. LRR B,E, MLRA 13, 47. The series is of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Franklin County, Idaho, 1997. The name is coined.
REMARKS: Diagnostic horizons and features recognized in this pedon:
Mollic epipedon - the zone from 1 to 24 inches (the A1, A2, and A3 horizons)
Argillic horizon - the zone from 24 to 63 inches (the Bt1, Bt2, and Bt3 horizons)
Particle-size control section - the zone from 24 to 44 inches (the Bt1, Bt2, and part of the Bt3 horizons)