LOCATION THREEK                  ID

Established Series
Rev. ALH/CLM
12/2019

THREEK SERIES

The Threek series consists of very deep, well drained soils with slow permeability that formed in mixed alluvium from volcanoclastic material. Threek soils are on sideslopes and summits of glacial valley trains and outwash terraces. Slopes are 2 to 40 percent. Average annual precipitation is about 360 mm and average annual temperature is about 6.1 degrees C.

TAXONOMIC CLASS: Clayey-skeletal, smectitic, frigid Typic Argixerolls

TYPICAL PEDON: Threek gravelly loam -- on a southwest-facing slightly convex slope of 11 percent, in native rangeland, at 1,825 meters elevation. (Colors are for air dry soils unless otherwise stated. When described on August 19, 1981, the soil was dry throughout.)

A1--0 to 8 cm; grayish brown (10YR 5/2) gravelly loam, very dark grayish brown (10YR 3/2) moist; moderate thin platy structure parting to weak fine granular; slightly hard, very friable, slightly sticky and slightly plastic; many very fine and fine, few medium roots; many very fine and fine vesicular pores; 25 percent gravel, 5 percent cobbles; neutral (pH 6.9); clear smooth boundary. (5 to 13 cm thick)

A2--8 to 18 cm; dark grayish brown (10YR 4/2) gravelly loam, very dark grayish brown (10YR 3/2) moist; moderate fine subangular blocky structure; slightly hard, very friable, moderately sticky and slightly plastic; common very fine and fine, few medium and coarse roots; common very fine and fine tubular pores; 20 percent gravel; neutral (pH 7.0); clear smooth boundary. (0 to 20 cm thick)

Bt1--18 to 33 cm; brown (10YR 5/3) very gravelly clay loam, dark brown (10YR 3/3) moist; moderate fine angular blocky structure; hard, friable, moderately sticky and moderately plastic; common very fine and fine, few medium and coarse roots; common very fine and fine tubular pores; many distinct clay films on faces of peds and in pores; 35 percent gravel, 5 percent cobbles; neutral (pH 7.1); clear smooth boundary. (10 to 25 cm thick)

Bt2--33 to 79 cm; light yellowish brown (10YR 6/4) very gravelly clay, yellowish brown (10YR 5/4) moist; strong fine angular blocky structure; very hard, firm, very sticky and very plastic; common very fine and fine roots; few very fine and fine tubular pores; continuous prominent clay films on faces of peds and in pores; 50 percent gravel, 5 percent cobbles; neutral (pH 7.3); clear wavy boundary. (25 to 78 cm thick)

2Bq--79 to 152 cm; reddish yellow (7.5YR 6/6) discontinuous weakly cemented extremely gravelly sandy loam, brown (7.5YR 4/4) moist; massive; hard, friable, nonsticky and nonplastic; few fine roots; few fine tubular pores; 60 percent gravel, 10 percent cobbles; neutral (pH 7.2).

TYPE LOCATION: Owyhee County, Idaho; about 3 1/2 miles east of Three Creek; about 2,000 feet north and 2,000 feet west of the southeast corner of section 31, T. 15 S., R. 12 E.; USGS Curtis Draw 7.5-minute topographic quadrangle; latitude 42 degrees 04 minutes 36 seconds N and longitude 115 degrees 05 minutes 40 seconds W; WGS84 Decimal Degrees 42.0766667 latitude, -115.0944444 longitude.

RANGE IN CHARACTERISTICS:

Mollic epipedon thickness - 25 to 41 cm.
Depth to lithologic discontinuity - 61 to 100 cm.
Particle-size control section - 35 to 50 percent clay; 35 to 60 percent rock fragments
Average annual soil temperature - 5.0 to 8.3 degrees C.
Average summer soil temperature - 16.1 to 19.4 degrees C.
Average annual precipitation - 300 to 430 mm. Soil Moisture: This soil is usually moist, but is dry for 45 to 70 consecutive days during the late summer and autumn. Typic xeric moisture regime.

A horizon
Value - 4 or 5 dry, 2 or 3 moist
Chroma - 2 or 3
Reaction (pH) - slightly acid or neutral

Bt horizon
Hue - 10YR or 7.5YR
Value - 4 through 6 dry, 3 through 5 moist
Chroma - 3 or 4
Texture - (upper part) GRV-CL or CBV-CL - 28 to 40 percent clay; (lower part) GRV-C or GRX-C - 40 to 55 percent clay
Reaction (pH) - neutral or mildly alkaline

2Bq horizon
Hue - 10YR or 7.5YR
Value - 4 through 6, 4 or 5 moist
Chroma - 4 through 6
Texture (fine-earth fraction) - SL, FSL, LS, or LFS
Rock fragments - 10 to 70 percent
Reaction (pH) - neutral to moderately alkaline

COMPETING SERIES: These are the Birchcreek, Derringer, Erakatak, Leevan, McIvey, Ravenswood, Roostercomb, Sharesnout, Yago, and Yeates Hollow series. Birchcreek, Derringer, Erakatak, Leevan, Ravenswood, Roostercomb, and Sharesnout soils have bedrock at depths of less than 100 cm. McIvey soils have argillic horizons that extend to depths of 150 cm or more and lack secondary silica. Yago soils lack secondary silica and the argillic has lime in the lower part. Yeates Hollow soils lack secondary silica and have argillic horizons that extend to bedrock.

GEOGRAPHIC SETTING: Threek soils occur on undulating to steep sideslopes and summits of glacial valley trains and outwash terraces at elevations of 1,465 to 1,830 meters. Slopes range from 2 to 40 percent. These soils formed in mixed alluvium from volcanoclastic material. The climate is cool and moist in the winter and hot and dry in the summer. Average annual precipitation is 300 to 430 mm and average annual temperature is 3.9 to 7.2 degrees C. The frost-free period is 60 to 95 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Barkley, Blackleg, Brunzell, and Doodlelink series. Barkley soils have less than 35 percent rock fragments in the control section and are on similar landscape positions. Blackleg soils have a duripan and are on similar landscape positions. Brunzell and Doodlelink soils lack argillic horizons and are on less exposed landscape positions.

DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY: Well drained; slow to rapid runoff; slow saturated hydraulic conductivity.

USE AND VEGETATION: Threek soils are used mainly for rangeland and wildlife habitat. The dominant natural vegetation is mountain big sagebrush, basin big sagebrush, Idaho fescue, and bluebunch wheatgrass.

DISTRIBUTION AND EXTENT: Southwestern Idaho. Threek soils are of small extent.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California

SERIES ESTABLISHED: Owyhee County Area, Idaho, 1992.

REMARKS: Diagnostic horizons and other features recognized in this pedon:
Mollic epipedon - The zone 0 to 33 cm (The A1, A2 and Bt1 horizons).
Argillic horizon - Thezone 18 to 79 cm (The Bt1 and Bt2 horizons).

Lithologic discontinuity - At 79 cm (The boundary at the top of the 2Bq horizon).

Particle-size control section - The zone 18 to 68 cm (The Bt1 and part of Bt2 horizons).

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National Cooperative Soil Survey
U.S.A.