LOCATION DOBSON                  ID

Established Series
Rev. MEJ/CLM/ALH/RWL
11/2010

DOBSON SERIES

The Dobson series consists of shallow, somewhat excessively drained soils with moderately rapid permeability that formed in colluvium and residuum from granitic rocks. Slopes range from 25 to 90 percent in foothills and canyons. The average annual precipitation is about 15 inches and the average annual temperature is about 49 degrees F.

TAXONOMIC CLASS: Loamy, mixed, superactive, mesic Aridic Lithic Haploxerolls

TYPICAL PEDON: Dobson fine gravelly coarse sandy loam -- on a 25 percent convex south-facing slope at 4,220 feet elevation in rangeland. When described on July 6, 1994, the soil was dry throughout. (Colors are for air-dry soil unless otherwise noted.)

A--0 to 2 inches; grayish brown (10YR 5/2) fine gravelly coarse sandy loam, dark brown (10YR 3/3) moist; weak fine granular structure; soft, very friable, slightly sticky and slightly plastic; common very fine and fine, few medium and coarse roots; many very fine irregular pores; 15 percent fine gravel; slightly acid (pH 6.1); clear smooth boundary. (2 to 7 inches thick)

Bw--2 to 12 inches; brown (10YR 5/3) fine gravelly coarse sandy loam, dark brown (10YR 3/3) moist; weak very fine and fine subangular blocky structure; slightly hard, very friable, slightly sticky and slightly plastic; common very fine and fine, few medium roots; common very fine and fine tubular pores; 15 percent fine gravel; neutral (pH 6.8); gradual wavy boundary. (6 to 13 inches thick)

BC--12 to 14 inches; very pale brown (10YR 7/4) fine gravelly loamy coarse sand, yellowish brown (10YR 5/4) moist; weak fine subangular blocky structure; hard, very friable, nonsticky and nonplastic; few very fine, fine and medium roots; many very fine and fine irregular pores; 25 percent fine gravel; neutral (pH 6.8); abrupt wavy boundary. (0 to 4 inches thick)

R--14 inches; unweathered granodiorite.

TYPE LOCATION: Boise County, Idaho; about 9 miles south and 1 mile west of Horseshoe Bend; 1,550 feet north and 1,350 feet west of the southeast corner of section 9, T.5 N., R.2 E.; USGS Cartwright Canyon Quadrangle; Latitude - 43 degrees, 46 minutes, 56 seconds N. and Longitude - 116 degrees, 13 minutes, 10 seconds W.; NAD 83.

RANGE IN CHARACTERISTICS:
Thickness of mollic epipedon - 7 to 12 inches
Depth to bedrock - 10 to 20 inches
Reaction - slightly acid or neutral
Base saturation (by sum of cations) - 50 to 75 percent in some part
Moisture control section - moist less than 90 consecutive days when the soil temperature is greater than 47 degrees F.
Average annual soil temperature - 47 to 54 degrees F.

A horizon
Value - 4 or 5 dry, 2 or 3 moist
Chroma - 2 or 3 dry or moist
Rock fragments - 15 to 30 percent gravel

Bw horizon
Value - 4 or 5 dry, 2 or 3 moist
Chroma - 2 or 3 dry or moist
Texture - COSL, SL or L
Clay content - 10 to 18 percent
Rock fragments - 15 to 30 percent gravel, 0 to 5 percent cobbles and 15 to 35 percent total

BC horizon (when present)
Value - 6 or 7 dry, 4 or 5 moist
Chroma - 2 through 4 dry or moist
Texture - COSL or LCOS
Clay content - 5 to 10 percent
Rock fragments - 15 to 30 percent gravel, 0 to 5 percent cobbles and 15 to 35 percent total

COMPETING SERIES: These are the Mcmullin, Reston and Whisk series. McMullin, Reston and Whisk soils have a xeric soil moisture regime. Reston soils do not have an activity class designated.

GEOGRAPHIC SETTING: Dobson soils are on south-facing, convex hill backslopes and shoulders and on canyon walls at elevations of 2,600 to 5,800 feet. Slopes range from 25 to 90 percent. These soils formed in colluvium and residuum from granitic rocks. The average annual precipitation is 12 to 20 inches. The average annual temperature is 45 to 52 degrees F. The frost-free period is 90 to 155 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Brownlee, Olaton, Robbscreek and Roney soils. Brownlee soils are deep and occur on gentle smooth and concave positions. Olaton soils are very deep, pachic and occur on north-facing slopes. Robbscreek and Roney soils are moderately deep and occur on similar geomorphic positions.

DRAINAGE AND PERMEABILITY: Well drained; medium to very rapid runoff; moderately rapid permeability.

USE AND VEGETATION: Dobson soils are used mainly for rangeland and wildlife habitat. Native vegetation is bluebunch wheatgrass, Thurber needlegrass, basin big sagebrush and antelope bitterbrush.

DISTRIBUTION AND EXTENT: West-central, Idaho. MLRA 10. Dobson soils are of moderate extent.

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

SERIES ESTABLISHED: Boise County Area, Idaho, Parts of Ada and Boise Counties, 2005.

REMARKS: Diagnostic horizons and features recognized in this pedon:
Mollic epipedon - zone from the surface to 12 inches (A and Bw horizons)
Lithic contact - at 14 inches (R)
Ultic subgroup criteria is also met
Particle-size control section - zone from the soil surface to 14 inches (When bedrock is 14 to 20 inches, the particle-size control section is from 10 inches to the lithic contact.)
Soil moisture regime - aridic bordering on xeric

These soils are drier than other Xerolls in the region under similar precipitation due to very low AWC, early runoff and extended period of high evapotranspiration.

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National Cooperative Soil Survey
U.S.A.