LOCATION BIGFLAT                 ID

Established Series
Rev. DJ/KL/PB/JVC
04/2018

BIGFLAT SERIES

The Bigflat series consists of deep to a duripan or very deep, well drained soils that formed in alluvium derived from basalt and loess derived from volcanic ash. Bigflat soils are on calderas, hills, and fan remnants. Slopes are 1 to 35 percent. The mean annual precipitation is about 300 mm and the mean annual temperature is about 6.1 degrees C.

TAXONOMIC CLASS: Fine, smectitic, frigid Aridic Palexerolls

TYPICAL PEDON: Bigflat silt loam--on a 1 percent slope, in native rangeland at 1,740 meters elevation. The surface has occasional stones. (When described on June 18, 1981, the soil was dry from 0 to 18 cm, slightly moist from 18 to 43 cm, and dry below. Colors are for dry soil unless otherwise noted.)

A--0 to 15 cm; brown (10YR 5/3) silt loam, dark brown (10YR 3/3) moist; weak medium subangular blocky structure parting to moderate fine granular; slightly hard, very friable, slightly sticky and slightly plastic; many very fine and fine roots; many very fine interstitial and tubular pores; neutral (pH 7.1); clear smooth boundary. (13 to 26 cm thick)

E--15 to 23 cm; pale brown (10YR 6/3) silt loam, dark brown (10YR 3/3) moist; moderate fine and medium subangular blocky structure; slightly hard, very friable, slightly sticky and slightly plastic; common very fine and fine, few medium roots; many very fine tubular pores; slightly alkaline (pH 7.8); abrupt smooth boundary. (0 to 8 cm thick)

Bt1--23 to 36 cm; yellowish brown (10YR 5/4) silty clay, dark yellowish brown (10YR 4/4) moist; strong fine prismatic structure parting to strong fine angular blocky; hard, firm, very sticky and very plastic; common very fine and fine roots; many very fine tubular pores; continuous prominent clay films on faces of peds and lining pores; moderately alkaline (pH 7.9); clear smooth boundary.

Bt2--36 to 48 cm; light yellowish brown (10YR 6/4) silty clay, dark yellowish brown (10YR 4/4) moist; weak fine prismatic structure parting to strong fine angular blocky; hard, firm, very sticky and very plastic; common very fine and few fine roots; common very fine tubular pores; continuous prominent clay films on faces of peds and lining pores; common fine rounded black iron-manganese concretions; moderately alkaline (pH 8.4); clear wavy boundary. (combined thickness of Bt horizons is 23 to 50 cm)

Bk1--48 to 100 cm; very pale brown (10YR 7/3) loam, yellowish brown (10YR 5/4) moist; massive; slightly hard, friable, slightly sticky and slightly plastic; few fine roots; many very fine tubular pores; strongly effervescent; strongly alkaline (pH 8.9); clear smooth boundary.

Bk2--100 to 122 cm; very pale brown (10YR 7/3) fine sandy loam, yellowish brown (10YR 5/4) moist; massive; slightly hard, very friable, nonsticky and nonplastic; few very fine and fine roots; common very fine tubular pores; 5 percent gravel; strongly effervescent; strongly alkaline (pH 8.9); abrupt wavy boundary. (combined thickness of the Bk horizons is 41 to 76 cm)

Bkqm--122 to 180 cm; white (10YR 8/2) extremely gravelly loamy sand, very pale brown (10YR 7/3) moist; strong thick platy structure; extremely strong, nonsticky and nonplastic; few very fine and fine roots matted between plates; many very fine and fine interstitial pores; 15 percent cobbles and 50 percent gravel which are cemented and indurated duripan fragments; strongly effervescent; strongly alkaline (pH 8.7).

TYPE LOCATION: Owyhee County, Idaho; about 4 miles east of Murphy Hot Springs; 2,600 feet east and 500 feet south of the northwest corner of section 9, T. 16 S., R. 10 E; USGS Murphy Hot Springs 7.5 minute topographic quadrangle; latitude 42 degrees 03 minutes 20 seconds N and longitude 115 degrees 17 minutes 42 seconds W; WGS84 Decimal Degrees 42.0555556 latitude, -115.2950000 longitude.
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RANGE IN CHARACTERISTICS:

Soil moisture - Usually dry, moist in winter and spring and dry in summer and fall; aridic moisture regime that borders on xeric.
Soil temperature - 5.6 to 8.3 degrees C.
Mean summer soil temperature - 17.8 to 19.4 degrees C.
Mollic epipedon - The zone from 0 to 23 cm (The A and E horizons when mixed).
Depth to abrupt textural change - 13 to 25 cm.
Argillic horizon - The zone from 23 to 48 cm (The Bt1 and Bt2 horizons)Depth to identifiable secondary carbonates - 38 to 76 cm.
Depth to secondary silica - 91 to 127 cm.
Depth to duripan - 100 to 152 cm in some pedons.

Control section - Clay content: 35 to 55 percent.


A horizon
Value: 2 or 3 moist.
Chroma: 2 or 3, dry or moist.
Rock fragments: 0 to 15 percent.
Reaction: Slightly acid to slightly alkaline.

Bt horizons
Value: 4 through 6 dry, 2 through 5 moist.
Chroma: 2 through 4, dry or moist.
Texture: Clay, silty clay, clay loam, silty clay loam, or cobbly clay.
Rock fragments: 0 to 25 percent, mainly cobbles composed of basalt.
Reaction: Neutral to moderately alkaline.
Other features: Some pedons have subhorizons with identifiable secondary carbonates .

Bk horizons
Value: 7 or 8 dry, 5 through 7 moist.
Chroma: 2 through 4, dry or moist.
Texture: Fine sandy loam, gravelly fine sandy loam, or gravelly loam.
Rock fragments: 0 to 35 percent.
Reaction: Moderately alkaline or strongly alkaline.
Effervescence: Strongly effervescent or violently effervescent.

Bkq horizon
Value: 6 through 8 dry, 4 through 7 moist.
Chroma: 2 through 6, dry or moist.
Texture: Very gravelly sandy loam, extremely gravelly loamy sand, very gravelly sandy clay loam, or very gravelly clay loam.
Rock fragments: 35 to 65 percent, mainly gravel some of which are pan fragments.
Reaction: Slightly alkaline to strongly alkaline.
Effervescence: Strongly effervescent or violently effervescent.
Other features: In some pedons, this horizon has continuous silica cementation or is indurated enough to be root-limiting and qualifies as a duripan.

COMPETING SERIES: This is the Hart series. Hart soils are deep to lithic contacts of hard tuff.

GEOGRAPHIC SETTING: Bigflat soils are on calderas, hills, and fan remnants. They formed in alluvium derived from basalt and loess derived from volcanic ash. Slopes are mainly 1 to 8 percent. There are small areas that have slopes up to 35 percent. Elevations range from 1,525 to 1,925 meters. The climate is semiarid with cold, moist winters and warm, dry summers. The mean annual precipitation is 280 to 330 mm, the mean annual temperature is 4.4 to 7.2 degrees C., and the frost-free period is 65 to 95 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Cleavage, Heckison, Insidert, and Thacker soils. Cleavage soils have more than 35 percent rock fragments in the control section and are on hills. Heckison, Insidert, and Thacker soils have duripans above 100 cm and are on similar landscape positions.

DRAINAGE AND PERMEABILITY: Well drained; high or very high surface runoff; very slow or slow permeability.

USE AND VEGETATION: Bigflat soils are used mainly for rangeland, cropland, and wildlife habitat. The dominant vegetation is Wyoming big sagebrush, bluebunch wheatgrass, Sandberg bluegrass, and western wheatgrass.

DISTRIBUTION AND EXTENT: Southwestern and east-central Idaho. Bigflat soils are moderately extensive. MLRAs 25 and 12.

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

SERIES ESTABLISHED: Owyhee County Area, Idaho, 1992.

REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - The zone from the soil surface to 18 cm (A and E horizons, mixed).
Abrupt texture change - The boundary at 23 cm (Bt1 horizon).
Argillic horizon - The zone from 23 to 48 cm (Bt1 and Bt2 horizons).
Palexeroll great group - There is an abrupt textural change at 23 cm with a clay increase of 15 percent or more (absolute) within one inch at the upper boundary of the argillic horizon (between the E and Bt1 horizons).

Particle-size control section - The zone from 23 to 48 cm (Bt1 and Bt2 horizons).

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National Cooperative Soil Survey
U.S.A.