LOCATION KOFFGO ID+MT

Established Series
Rev. JD-KTS-RJS
06/2011

KOFFGO SERIES

The Koffgo series consists of very deep, well drained soils on canyonsides, tablelands, plateaus, hills and mountain slopes. They formed in volcanic ash over slope alluvium, colluvium or residuum derived from mixed sources. Slopes are 2 to 70 percent. Permeability in the surface is moderate and moderately rapid in the subsoil and substratum. Mean annual precipitation is about 27 inches. Mean annual air temperature is about 36 degrees F.

TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive Vitrandic Haplocryepts

TYPICAL PEDON: Koffgo ashy silt loam, on a 6 percent convex ridge in an area of lodgepole pine/pinegrass plant community type at an elevation of 6,360 feet. (Colors are for dry soil unless otherwise stated.)

Oi--0 to 1 inch; forest litter; needles, cones, and twigs.

A--1 to 5 inches; grayish brown (10YR 5/2) ashy silt loam, dark brown (10YR 3/3) moist; weak fine subangular blocky structure parting to weak medium granular; soft, very friable, slightly sticky and slightly plastic; many very fine and fine and common medium and coarse roots; many very fine irregular pores; 5 percent gravel; moderately acid (pH 5.6); clear broken boundary. (2 to 10 inches thick)

Bw1--5 to 13 inches; light gray (10YR 7/2) gravelly ashy silt loam, brown (10YR 5/3) moist; moderate medium subangular blocky structure; slightly hard, friable, nonsticky and slightly plastic; common very fine through coarse roots; common very fine irregular pores; 20 percent gravel; moderately acid (pH 5.8); clear smooth boundary.

Bw2--13 to 19 inches; light brownish gray (10YR 6/2) gravelly ashy silt loam, brown (10YR 5/3) moist; moderate medium subangular blocky structure; slightly hard, friable, nonsticky and slightly plastic; few very fine through coarse roots; common very fine irregular pores; 25 percent gravel; moderately acid (pH 5.8); clear smooth boundary. (combined thickness of the Bw horizons is 7 to 30 inches)

BC--19 to 51 inches; light gray (10YR 7/1) extremely flaggy sandy loam, grayish brown (10YR 5/2) moist; massive; soft, very friable, nonsticky and nonplastic; common very fine and fine and few medium and coarse roots; few fine brown (7.5YR 4/3) moist clay films on undersides of rocks; 20 percent gravel, 40 percent flagstones, and 20 percent channers; moderately acid (pH 6.0); diffuse wavy boundary. (17 to 50 inches thick)

C--51 to 60 inches; white (N 8/) fragmental rhyolite, gray (N 5/) moist; 20 percent gravel, 70 percent flaggstones, and 5 percent channers; few very fine and fine roots occuring in fractures and hanging in voids; few fine brown (7.5YR 4/3) moist clay films on undersides of rocks and on top of rocks under silt like films; 5 percent irregular coarse voids between rock fragments; no fine earth material in voids.

TYPE LOCATION: Fremont County, Idaho; about 27 miles north of Ashton; about 1000 feet north and 2000 feet west of the southeast corner of section 11, T. 13 N., R. 43 E.; Latitude - 44 degrees, 27 minutes, 40 seconds north; Longitude - 111 degrees, 20 minutes, 35 seconds west.

RANGE IN CHARACTERISTICS:

Mean annual soil temperature - 36 to 40 degrees F.
Mean summer soil temperature - 42 to 46 degrees F.
Moisture control section - between 8 and 24 inches; dry throughout the moisture control section for 15 to 45 consecutive days during the four months following the summer solstice
Depth to fragmental material - 40 to greater than 60 inches
Volcanic glass content - 5 to 30 percent in the 0.02 to 2.0 mm fraction
Ammonium oxalate extractable Al plus 1/2 Fe - 0.1 to 1.0 percent
Phosphate retention - 20 to 50 percent

A horizon - Value: 4 to 6 dry, 2 to 4 moist
Chroma: 1 to 3 dry and moist
Clay content: 7 to 16 percent
Rock fragment content: 0 to 35 percent
Gravel: 0 to 35 percent
Cobbles: 0 to 10 percent
Stones or boulders: 0 to 5 percent
Base saturation by ammonium acetate: 30 to 60 percent
Reaction: strongly acid or moderately acid

Bw horizon - Hue: 2.5Y or 10YR
Value: 5, 6 or 7 dry, 4 or 5 moist
Chroma: 2 to 4 dry and moist
Texture, less than 2mm fraction: ashy loam, ashy sandy loam, or ashy silt loam
Clay content: 4 to 14 percent
Rock fragments: 15 to 90 percent
Gravel: 5 to 60 percent
Cobbles: 5 to 55 percent
Stones: 0 to 40 percent
Base saturation by ammonium acetate: 50 to 80 percent
Reaction: moderately acid or slightly acid

BC horizon - Hue: 5Y, 2.5Y or 10YR
Value: 6 or 7 dry, 4 to 6 moist
Chroma: 1 to 4 dry or moist
Rock fragments: 45 to 90 percent
Gravel and channers: 5 to 40 percent
Cobbles: 0 to 65 percent
Stones or boulders: 5 to 85 percent
Base saturation by ammonium acetate: 60 to 100 percent
Reaction: moderately acid to neutral

C horizon - Rock fragments: 90 to 100 percent

COMPETING SERIES: These are the Frankcreek, Hartop, Judco, and Torpy series. The Frankcreek and Hartop soils have a xeric moisture regime. The Judco and Torpy soils have an ustic moisture regime.

GEOGRAPHIC SETTING:
Landform - canyonsides, tablelands, plateaus, hills and mountain slopes
Elevation - 5,300 to 9,800 feet
Slope - 2 to 70 percent
Parent material - volcanic ash over slope alluvium, colluvium or residuum derived from mixed sources
Mean annual precipitation - 22 to 44 inches
Mean annual air temperature - 34 to 38 degrees F.
Frost-free period - less than 70 days

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Fitzwil, Flatrock and Rhylow soils. They are intermixed with the Koffgo soils. Fitzwil and Flatrock soils have argillic horizons. Rhylow soils have an umbric epipedon.

DRAINAGE AND PERMEABILITY: Well drained; slow to very rapid runoff; permeability is moderate in the surface and moderately rapid in the subsoil and substratum.

USE AND VEGETATION: Recreation, woodland and wildlife habitat. Potential vegetation is various subalpine fir plant associations. Present vegetation is various lodgepole pine and subalpine fir communities.

DISTRIBUTION AND EXTENT: These soils are of small extent in Eastern Idaho and western Montana. MLRAs - 12, 43B.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana.

SERIES ESTABLISHED: Targhee National Forest, 1997; proposed in Lemhi County, Idaho, 1984, type location moved to the Targhee National Forest, Fremont, County, Idaho 1994.

REMARKS: Diagnostic features recognized in this pedon are:
Ochric epipedon - The zone from 1 to 5 inches (A horizon)
Vitrandic subgroup feature - The zone from 1 to 19 inches (A, Bw1, and Bw2 horizons)
Cambic horizon - The zone from 5 to 19 inches (Bw1 and Bw2 horizons)
Particle-size control section - the zone from 11 to 41 inches (part of the Bw1, the Bw2, and part of the BC horizons)

ADDITIONAL DATA: Full characterization data (8/96) NSSL, Lincoln, NE. Client assigned lab number S94ID-043-004.
Project file number: 95P 27. Lab assigned number: Pedon 95P 151. Samples: 95P 1035-1038.

Koffgo soils have a cryic temperature regime and an udic moisture regime.

The 3/2008 description reflects a change in classification from Loamy-skeletal, mixed, superactive Vitrandic Eutrocryepts to Loamy-skeletal, mixed, superactive Vitrandic Haplocryepts due to revision of the cryepts great groups and subgroups. The competing series section was not updated and should be reviewed after all the cryepts have been re-classified.

National Cooperative Soil Survey
U.S.A.