LOCATION TOHONA                  UT+NM

Established Series
Rev. JVC/LWH/MJD/DKR/WWJ
10/2013

TOHONA SERIES

The Tohona series consists of well drained, slowly permeable, sodic soils which are moderately deep to soft bedrock. Tohona soils formed in alluvium, slope alluvium and residuum derived from shale, claystone, and sandstone. These soils occur on dipslopes of cuestas, summits of structural benches, and footslopes below mesas. Slopes are 1 to 12 percent. Mean annual precipitation is about 7 inches (178 mm); and mean annual temperature is about 53 degrees F (12 degrees C).

TAXONOMIC CLASS: Fine, smectitic, mesic Vertic Natrigypsids

TYPICAL PEDON: Tohona sandy clay loam -- on the summit of a structural bench sloping 4 percent to the south at 5,010 feet elevation -- rangeland. (Colors are for dry soil unless otherwise noted.)

A-- 0 to 1 inch (0 to 3 cm); light brown (7.5YR 6/4) sandy clay loam, brown (7.5YR 4/4) moist; moderate very thick platy structure parting to weak very fine granular; slightly hard, friable, slightly sticky and slightly plastic; few fine roots; common vesicular pores; 5 percent gravel; slightly effervescent; moderately alkaline (pH 8.2); abrupt smooth boundary. (0 to 2 inches thick)

Btn-- 1 to 4 inches (3 to 10 cm); light reddish brown (5YR 6/4) clay, yellowish red (5YR 4/6) moist; strong medium prismatic structure; very hard, very firm, very sticky and very plastic; few fine roots; common fine and very fine tubular pores; few cracks 0.25 to 0.5 inch wide filled with A horizon material; common thin clay films on faces of peds and in pores; strongly effervescent; very strongly alkaline (pH 9.2); clear wavy boundary. (3 to 5 inches thick)

Btkn-- 4 to 16 inches (10 to 41 cm); light reddish brown (5YR 6/4) clay, yellowish red (5YR 5/6) moist; moderate medium prismatic structure parting to weak coarse subangular blocky; very hard, very firm, very sticky and very plastic; few fine and very fine roots; few fine and very fine tubular pores; few fine clay films on faces of peds and in pores; strongly effervescent, secondary calcium carbonates segregated in few fine irregularly shaped accumulations on faces of peds; very strongly alkaline (pH 9.2); clear smooth boundary. (7 to 12 inches thick)

Bky-- 16 to 28 inches (41 to 71 cm); pink (5YR 7/3) silty clay, reddish brown (5YR 5/4) moist; moderate medium prismatic structure parting to weak medium subangular blocky; very hard, very firm, very sticky and very plastic; few fine and very fine roots; few very fine tubular pores; 10 percent soft shale fragments; secondary gypsum crystals segregated in few fine irregularly shaped accumulations on faces of peds; strongly effervescent, secondary calcium carbonates segregated in few fine and medium irregularly shaped accumulations on faces of peds; strongly alkaline (pH 9.0); clear wavy boundary. (0 to 12 inches thick)

2By-- 28 to 34 inches (71 to 86 cm); light gray (10YR 7/1) silty clay loam, gray (10YR 6/1) moist; moderate very coarse prismatic structure; hard, firm, sticky and plastic; few fine and very fine roots; very few very fine tubular pores; 50 percent soft shale fragments; secondary gypsum crystals segregated in common medium and large irregularly shaped accumulations on faces of peds and shale fragments; slightly effervescent; moderately alkaline (pH 8.2); gradual wavy boundary. (6 to 10 inches thick)

2BCy-- 34 to 38 inches (86 to 97 cm); light gray (10YR 7/2) with light red (10R 6/6) silty clay loam, light brownish gray (10YR 6/2) with red (10R 5/6) moist; massive, platy rock structure; hard, firm, sticky and plastic; few very fine roots; very few irregularly shaped pores; 70 percent soft shale fragments; secondary gypsum crystals segregated in common fine and medium irregularly shaped accumulations on faces of peds and shale fragments; very slightly effervescent; slightly alkaline (pH 7.8); gradual wavy boundary. (4 to 14 inches thick)

2Cr-- 38 inches (97 cm); platy, bentonitic shale bedrock.

TYPE LOCATION: San Juan County, Utah; on the Navajo Indian Reservation about 5 miles north of Aneth community; 1,200 feet south of the north quarter corner of section 28, T.40S., R.25E.

RANGE IN CHARACTERISTICS:
Soil moisture - Typically, the soil moisture control section (SMCS) is intermittently moist in the upper part from July to October and December to April. The SMCS is dry in all parts greater than 75 percent of the time (cumulative), when the soil temperature at 20 inches is 41 degrees F or higher. Typic aridic moisture regime.

Soil temperature - 54 to 57 degrees F (12 to 14 degrees C)

Soil depth - 20 to 40 inches (51 to 102 cm); to soft bedrock

Depth to base of natric horizon - 10 to 19 inches (25 to 48 cm)

Depth to gypsic horizon - 10 to 24 inches (25 to 61 cm)

Reaction - slightly alkaline to very strongly alkaline

A horizon
Hue: 5YR, 7.5YR
Value: 5 or 6 dry, 4 or 5 moist
Chroma: 3 to 6, dry or moist
Texture: sandy clay loam or very gravelly sandy clay loam
Organic carbon content: 0.23 to 0.35 percent
Electrical conductivity: 0 to 2 (mmhos/cm)
Sodium adsorption ratio: 0 to 5
Rock fragments: 5 to 50 percent gravel, and 0 to 10 percent cobbles

Btn and Btkn horizons
Hue: 5YR or 7.5YR
Value: 5 or 6 dry, 4 or 5 moist
Chroma: 4 to 6, dry or moist
Clay content: 40 to 60 percent
Organic carbon content: 0.23 to 0.35 percent
Electrical conductivity: 0 to 4 (mmhos/cm)
Sodium adsorption ratio: 13 to 30
Calcium carbonate equivalence: 5 to 15 percent
Rock fragments: 0 to 10 percent gravel, and 0 to 5 percent cobbles. Other features: cracks less than 1 inch wide are evident when dry

Bky horizon
Hue: 5YR or 7.5YR
Value: 6 or 7 dry, 5 or 6 moist
Chroma: 3 to 6, dry or moist
Texture: clay or silty clay
Clay content: 40 to 60 percent
Organic carbon content: 0.10 to 0.29 percent
Electrical conductivity: 4 to 8 (mmhos/cm)
Sodium adsorption ratio: 13 to 30
Calcium carbonate equivalence: 5 to 10 percent
Gypsum content: 2 to 5 percent
Other features: 0 to 15 percent soft shale fragments

By and 2BCy horizons
Hue: 10R through 5GY
Value: 6 or 7 dry, 5 or 6 moist
Chroma: 1 to 6, dry or moist
Texture: gyp silty clay loam or gyp clay loam
Clay content: 35 to 40 percent
Organic carbon content: 0.10 to 0.29 percent
Electrical conductivity: 8 to 16 (mmhos/cm)
Sodium adsorption ratio: 5 to 13
Calcium carbonate equivalence: 2 to 5 percent
Gypsum content: 15 to 30 percent
Other features: 15 to 70 percent soft shale fragments

COMPETING SERIES: This is the Oagamati (CO) series. Oagamati soils do not have horizons redder than 10YR.

GEOGRAPHIC SETTING: Tohona soils are on dipslopes of cuestas, summits of structural benches, and footslopes below mesas. They formed in alluvium and residuum derived from Jurassic bentonitic shale, claystone, and sandstone. Slopes range from 1 to 12 percent. Elevation ranges from 4,600 to 5,550 feet (1,402 to 1,692 meters). The mean annual precipitation is 6 to 10 inches (152 to 254 mm); with 35 to 60 percent falling as rain from high-intensity thunderstorms between July and September. The mean annual temperature is 52 to 58 degrees F (11 to 14 degrees C);. The average frost-free period is 130 to 180 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Claysprings, Hoskinnini, and Whit soils; and Badland. Claysprings soils are shallow and occur on adjacent backslopes. Hoskinnini soils are very shallow and occur on adjacent structural benches. Whit soils are very deep and occur on eolian-mantled surfaces. Badland occurs on steep, barren hills of shale and claystone.

DRAINAGE AND PERMEABILITY: Well drained; rapid runoff; slow permeability

USE AND VEGETATION: Tohona soils are used for livestock grazing. Present vegetation is galleta, alkali sacaton, sand dropseed, bottlebrush squirreltail, cheatgrass, mound saltbush, and shadscale.

DISTRIBUTION AND EXTENT: Tohona soils are of moderate extent on the Blanding Basin portion of the Colorado Plateau province in southeast Utah, northwest New Mexico, and northeast Arizona. Tohona soils also occur on the adjacent Ute Mountain Ute Indian Reservation in southwest Colorado. LRR-D, MLRA 35.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Phoenix, Arizona

SERIES ESTABLISHED: Soil Survey of Navajo Indian Reservation, San Juan County, Utah, 1972.

REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - The zone from the soil surface to a depth of about 1 inch (3 cm); (A horizon)
Natric horizon - The zone from 1 to about 16 inches (3 to 41 cm); (Btn and Btkn horizons)
Gypsic horizon - The zone from 28 to about 38 inches (71 to 97 cm); (By and 2BCy horizons)
Paralithic contact - The presence of soft shale bedrock at about 38 inches (97 mm)
Vertic features: The presence of cracks from 1 to 4 inches and a linear extensibility of 6.0 cm or more between the soil surface and a paralithic contact. (Btn and Btkn horizons)

The classification was changed from fine-silty, mixed, mesic Cambic Gypsiorthids to fine, montmorillonitic, mesic Typic Natrargids in 1992.

The classification was changed from fine, montmorillonitic, mesic Typic Natrargids to fine, smectitic, mesic Typic Natrargids in February 1997.

The classification was changed from fine, smectitic, mesic Typic Natrargids to fine, smectitic, mesic Typic Natrigypsids in June 2004.

The classification was changed from fine, smectitic, mesic Typic Natrigypsids to fine, smectitic, mesic Vertic Natrigypsids in January 2005.

ADDITIONAL DATA: Reference samples were taken of the Btn and Btkn horizons at the series type location. Analysis for determination of sodium adsorption ratio was performed at the BIA soils lab in Gallup, NM as sample S88NM-045-4. The results confirm the moderately sodic Sodicity class. Calcium carbonate equivalence determined with a field volume calcimeter. Salinity values were determined with an Instant EC Salinity kit.

Classified according to Soil Taxonomy Second Edition, 1999; Keys to Soil Taxonomy 11th Edition, 2010.

Revised for the correlation the SDJR - MLRA 35 - Tohona-Kimnoli-Claysprings complex, 2 to 45 percent slopes project, September 2013, LJG2

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National Cooperative Soil Survey
U.S.A.