LOCATION FORTBOIS                ID

Established Series
Rev. ALH/RWL
07/2012

FORTBOIS SERIES

The Fortbois series consists of very deep, somewhat excessively drained soils with moderately rapid permeability that formed in colluvium from lacustrine deposits. Slopes range from 50 to 90 percent in foothills. The average annual precipitation is about 14 inches and the average annual temperature is about 52 degrees F.

TAXONOMIC CLASS: Sandy, mixed, mesic Xeric Haplocambids

TYPICAL PEDON: Fortbois loamy sand -- on a slightly convex south-facing slope of 60 percent, in rangeland at 3,150 feet elevation. When described on August 28, 1995, the soil was dry throughout. (Colors are for air-dry soil unless otherwise stated.)

A1--0 to 2 inches; grayish brown (10YR 5/2) loamy sand, very dark grayish brown (10YR 3/2) moist; weak fine subangular blocky structure parting to single grain; soft, very friable, nonsticky and nonplastic; many very fine and fine, few medium roots; many very fine and fine, common medium irregular pores; 10 percent gravel; slightly acid (pH 6.1); abrupt smooth boundary.

A2--2 to 7 inches; brown (10YR 5/3) loamy sand, dark brown (10YR 3/3) moist; weak fine and medium subangular blocky structure; soft, very friable, nonsticky and nonplastic; many very fine and fine, few medium roots; common very fine and fine, few medium irregular pores; slightly acid (pH 6.2); abrupt smooth boundary. (combined A - 3 to 8 inches thick)

Bw--7 to 11 inches; light brownish gray (10YR 6/2) sandy loam, dark grayish brown (10YR 4/2) moist; moderate fine and medium subangular blocky structure; slightly hard, friable, nonsticky and nonplastic; common very fine and fine, few medium roots; common very fine and fine irregular, few very fine and fine tubular pores; neutral (pH 6.9); abrupt smooth boundary. (3 to 10 inches thick)

BC--11 to 17 inches; pale brown (10YR 6/3) loamy sand, brown (10YR 5/3) moist; weak medium subangular blocky structure; slightly hard, very friable, nonsticky and nonplastic; common very fine and fine, few medium roots; common very fine and fine, few medium irregular pores; neutral (pH 6.8); clear smooth boundary. (0 to 10 inches thick)

C--17 to 60 inches; very pale brown (10YR 7/3) sand, pale brown (10YR 6/3) moist; massive; slightly hard, friable, nonsticky and nonplastic; few very fine, fine and medium roots; few fine slightly effervescent masses and seams of segregated calcium carbonates; neutral (pH 6.8).

TYPE LOCATION: Ada County, Idaho; in Boise; 150 feet south and 850 feet west of the northeast corner of section 35, T.4 N., R.2 E.; USGS Boise North Quadrangle; (Latitude - 43 degrees, 38 minutes, 51 seconds N. and Longitude - 116 degrees, 10 minutes, 34 seconds W.)

RANGE IN CHARACTERISTICS:
Depth to base of cambic horizon - 10 to 18 inches
Particle-size control section - 2 to 8 percent clay (greater than 50 percent fine or coarser sand)
Moisture control section - moist less than 90 consecutive days when the soil temperature is greater than 47 degrees F. and dry about 120 to 150 days when soil temperature is above 41 degrees F.
Average annual soil temperature - 53 to 55 degrees F

A horizon
Chroma - 2 or 3 dry or moist
Rock fragment content - 0 to 15 percent gravel
Reaction (pH) - slightly acid or neutral

Bw horizon
Value - 5 or 6 dry
Chroma - 2 to 4 dry or moist
Texture - SL or COSL
Clay content - 5 to 10 percent
Rock fragment content - 0 to 10 percent gravel
Reaction (pH) - slightly acid to slightly alkaline

C horizon
Hue - 2.5Y to 7.5YR
Value - 6 or 7 dry, 5 or 6 moist
Chroma - 3 or 4 dry or moist
Texture - S, LS or LCOS
Clay content - 1 to 8 percent
Rock fragment content - 0 to 10 percent gravel
Calcium carbonate equivalent - 0 to 5 percent
Reaction (pH) - slightly acid to slightly alkaline

COMPETING SERIES: These are the Davey and Timmerman series. Davey soils have color value greater than 5.5 in the A horizon, an average annual soil temperatures of 47 to 53 degrees F. and are dry about 150 to 180 consecutive days when soil temperature is above 41 degrees F. Timmerman soils have secondary carbonates (Bk horizons) at a depth of 13 to 30 inches.

GEOGRAPHIC SETTING: Fortbois soils are very steep on hill backslopes and gulch slopes at elevations of 2,700 to 3,850 feet. Slopes range from 50 to 90 percent. These soils formed in colluvium from lacustrine deposits. The climate is cool and moist in the winter and warm and dry in the summer. Average annual precipitation ranges from 12 to 16 inches. Average annual temperature ranges from 51 to 53 degrees F. Frost-free period is 140 to 155 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Flofeather and Quailridge soils. Flofeather soils have thick mollic epipedons and are on alluvial fans. Quailridge soils have mollic epipedons, more than 18 percent clay in the particle-size control section and are on less steep landscape positions.

DRAINAGE AND PERMEABILITY: Somewhat excessively drained; rapid runoff; moderately rapid permeability.

USE AND VEGETATION: Fortbois soils are used mainly for rangeland and wildlife habitat. The dominant natural vegetation is Antelope bitterbrush, bottlebrush squirreltail and needleandthread grass.

DISTRIBUTION AND EXTENT: Southwestern Idaho. MLRA 10. Fortbois soils are not extensive.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon

SERIES ESTABLISHED: Ada County, Idaho, 2012.

REMARKS: Diagnostic horizons and features recognized in this pedon:

Ochric epipedon - zone 0 to 7 inches (A1 and A2 horizons)
(too thin to qualify as mollic epipedon)

Cambic horizon - zone 7 to 11 inches (Bw horizon)

Particle-size control section - zone 10 to 40 inches

Soil moisture regime - aridic bordering xeric

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National Cooperative Soil Survey
U.S.A.