LOCATION TWEBA                   NV

Established Series
Rev. SES/CEF/RLB/JBF
12/2019

TWEBA SERIES

The Tweba series consists of very deep, very poorly drained soils that formed in alluvium derived from mixed rocks. Tweba soils are on flood plains stream flood plains and inset fans. Slopes are 0 to 2 percent. The mean annual precipitation is about 230 mm and the mean annual temperature is about 9 degrees C.

TAXONOMIC CLASS: Coarse-loamy, mixed, superactive, calcareous, mesic Aeric Fluvaquents

TYPICAL PEDON: Tweba very fine sandy loam--rangeland. (Colors are for dry soil unless otherwise noted.)

A--0 to 3 cm; light gray (2.5Y 7/2) very fine sandy loam overwash, grayish brown (2.5Y 5/2) moist; massive; soft, very friable, slightly sticky and slightly plastic; many very fine and fine roots; many very fine tubular pores; 0.6 to 1.2 cm layer of undecomposed organic matter on the surface; strongly effervescent; moderately alkaline (pH 8.2); abrupt smooth boundary. (3 to 18 cm thick)

C1--3 to 15 cm; light brownish gray (2.5Y 6/2) very fine sandy loam, dark grayish brown (2.5Y 4/2) moist; common fine distinct brown (10YR 4/3) and few fine faint dark brown (10YR 3/3) moist iron redox concentrations; massive; slightly hard, friable, nonsticky and slightly plastic; many very fine, fine and medium roots; many very fine tubular pores; strongly effervescent; strongly alkaline (pH 8.6); clear wavy boundary. (8 to 36 cm thick)

C2--15 to 30 cm; light brownish gray (2.5Y 6/2) silt loam, dark grayish brown (2.5Y 4/2) moist; common fine distinct yellowish brown (10YR 5/4) and few fine faint dark brown (10YR 3/3) moist iron redox concentrations; weak medium prismatic structure with weak and moderate thin and medium platy fine stratification in place; hard, friable, moderately sticky and moderately plastic; common very fine and fine roots; common very fine and few fine tubular pores; strongly effervescent; very strongly alkaline (pH 9.2); clear wavy boundary. (10 to 30 cm thick)

C3--30 to 48 cm; light brownish gray (2.5Y 6/2) silt loam, dark grayish brown (2.5Y 4/2) moist; common fine distinct yellowish brown (10YR 5/6) and brown (7.5YR 4/4) moist iron redox concentrations; massive with weak very thin and thin platy stratification; hard, friable, moderately sticky and moderately plastic; few very fine roots; many very fine and fine tubular pores; common faint films lining fine pores; 2.5 cm thick lens of silty clay loam along the upper boundary; strongly effervescent; very strongly alkaline (pH 9.2); abrupt wavy boundary. (13 to 25 cm thick)

C4--48 to 86 cm; light brownish gray (2.5Y 6/2) fine sandy loam, grayish brown (2.5Y 5/2) moist; common fine and medium distinct strong brown (7.5YR 5/6) and brown (7.5YR 4/4), dark yellowish brown (10YR 4/4) moist iron redox concentrations; massive; slightly hard, very friable, slightly sticky and slightly plastic; few very fine and fine roots; many very fine and fine tubular pores; 1 cm thick horizontal lens of charcoal; many mica particles; strongly effervescent; very strongly alkaline (pH 9.4); gradual wavy boundary. (28 to 58 cm thick)

C5--86 to 150 cm; light gray (10YR 7/1) and light brownish gray (2.5Y 6/2) stratified very fine sandy loam and loamy sand, grayish brown (10YR 5/2) and grayish brown (2.5Y 5/2) moist; common fine and medium distinct brown (7.5YR 5/4), strong brown (7.5YR 5/6) and dark brown (10YR 3/3), dark yellowish brown (10YR 4/4) moist redox concentrations; massive; slightly hard or hard, very friable, nonsticky and slightly sticky, nonplastic and slightly plastic; few very fine roots; many very fine and fine tubular pores, common faint films lining fine pores; many mica particles; strongly effervescent; strongly alkaline (pH 8.6).

TYPE LOCATION: Elko County, Nevada; about 18 miles south of Elko, near Twin Bridges on Huntington Creek; approximately 1,850 feet east and 1,590 feet north of the approximate southwest corner of section 36, T.32 N., R.55 E.; USGS West of Lee 7.5 minute topographic quadrangle; latitude 40 degrees 36 minutes 42 seconds N and longitude 115 degrees 43 minutes 56 seconds W; WGS84 Decimal Degrees 40.6116667 latitude, -115.7322222 longitude.

RANGE IN CHARACTERISTICS:
Soil moisture: Dry in midsummer and early fall, moist in late fall, winter, spring and early summer, apparent seasonal water table is between a depth of 36 to 50 cm for some time during most years usually February to June. Drained phases are recognized.
Mean annual soil temperature: 8 to 11 degrees C.
Other features: In some pedons, one or more buried A horizons with hue of 10YR or 5Y, value of 5 or 6 dry and 3 moist, chroma of 1 or 2 are below a depth of 30 cm.

Particle-size control section - Clay content: Averages 10 to 18 percent.

A horizon
Hue: 2.5Y or 10YR.
Value: 5 through 7 dry, 3 through 5 moist.
Chroma: 2 or 3.
Reaction: Slightly alkaline through strongly alkaline.
Effervescence: Noneffervescent through strongly effervescent.
Organic matter: 2 to 4 percent.

C horizon
Hue: 2.5Y or 10YR.
Value: 6 or 7 dry, 4 or 5 moist.
Chroma: 1 through 3 dry, and 2 or 3 moist.
Texture: Average fine sandy loam or very fine sandy loam, but includes stratified very fine sandy loam, fine sandy loam, loam or silt loam in the upper subhorizons and very fine sandy loam, fine sandy loam, sandy loam, loamy fine sand or loamy sand in the lower subhorizons. Loamy fine sand and loamy sand are more common below 89 cm.
Reaction: Slightly alkaline through very strongly alkaline.
Effervescence: Slightly effervescent through strongly effervescent to a depth of 75 to 114 cm and noneffervescent through strongly effervescent below.
Organic matter: Less than 2 percent.

COMPETING SERIES: These are the Bigwinder and Mirada series.

Bigwinder soils average 2 to 4 percent organic matter throughout the profile. Miranda soils have less than 10 percent clay in the particle-size control section.

GEOGRAPHIC SETTING: Tweba soils are on floodplains and along inset fans. These soils formed in alluvium derived from mixed rocks. Slopes are 0 to 2 percent. Elevations are 1,345 to 1,710 meters. The climate is cool, semiarid with cool, moist winters and warm, dry summers. The mean annual precipitation is 200 to 250 mm, mean annual temperature is 8 to 10 degrees C, and the frost-free season is 100 to 120 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Bloor, Ocala and Provo soils. Bloor soils are moderately well drained and have a sodium affected Btn horizon. Ocala soils have a fine-silty particle-size control section and weak silica cemented Bq horizons. Provo soils have a sandy-skeletal particle-size control section.

DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY: Very poorly drained; very slow or slow runoff; moderately high saturated hydraulic conductivity. In some areas the drainage has been altered by channel entrenchment and natural stream realignment. Seasonal water table is 36 to 50 cm.

USE AND VEGETATION: Rangeland and wildlife habitat. The present vegetation is mainly big sagebrush, rubber rabbitbrush, basin wildrye, creeping wildrye and saltgrass.

DISTRIBUTION AND EXTENT: Northeastern Nevada. MLRA 25, 24. These soils are not extensive.

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

SERIES ESTABLISHED: Lander County, Nevada, North Part, 1985.

REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - The zone from the surface to 18 cm (A, C1 and part of C2 horizon).
Zone of Endosaturation - The zone from 3 to 150 cm (C1, C2, C3, C4 and C5 horizons).
Seasonal high water table - Within a depth of 36 to 50 cm.
Particle-size control section - The zone from 25 to 100 cm (C3, C4, and parts of the C2 and C5 horizons).

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National Cooperative Soil Survey
U.S.A.