LOCATION MOPANA                  NV+CA

Established Series
Rev. EWB-WED-JVC-JBF
04/2017

MOPANA SERIES

The Mopana series consists of shallow to a duripan, well drained soils that formed in eolian volcanic ash over residuum derived from basalt. Mopana soils are on plateaus. Slopes are 0 to 15 percent. The mean annual precipitation is about 330 mm and the mean annual temperature is 6 degrees C.

TAXONOMIC CLASS: Clayey, smectitic, frigid, shallow Vitritorrandic Durixerolls

TYPICAL PEDON: Mopana ashy fine sandy loam--rangeland. (Colors are for dry soil unless otherwise noted.) The soil surface is covered with 2 percent stones, 5 percent cobbles, and 15 percent gravel.

A--0 to 10 cm; brown (10YR 5/3) ashy fine sandy loam, dark brown (10YR 3/3) moist; weak medium subangular blocky structure; soft, very friable, slightly sticky and nonplastic; many very fine and common fine roots; common very fine interstitial and few very fine tubular pores; 10 percent gravel; neutral (pH 7.0); clear wavy boundary. (3 to 13 cm thick)

BAt--10 to 20 cm; brown (10YR 5/3) ashy loam, dark brown (10YR 3/3) moist; moderate fine and medium subangular blocky structure; soft, very friable, slightly sticky and slightly plastic; common very fine to medium roots; few very fine interstitial and common very fine tubular pores; few distinct and common faint clay films on faces of peds; 5 percent gravel and 5 percent cobbles; neutral (pH 7.0); abrupt wavy boundary. (8 to 13 cm thick)

2Bt--20 to 43 cm; brown (7.5YR 5/4) clay, dark brown (7.5YR 3/4) moist; strong fine and medium prismatic structure parting to strong fine and medium angular blocky; very hard, very firm, very sticky and very plastic; few very fine roots between peds; common very fine tubular pores; prominent pressure cutans on faces of peds; 5 percent gravel and 5 percent cobbles; neutral (pH 7.0); clear wavy boundary. (15 to 30 cm thick)

2Btqk--43 to 48 cm; light brown (7.5YR 6/4) very gravelly clay loam, brown (7.5YR 4/4) moist; moderate medium platy structure; hard, friable, moderately sticky and moderately plastic; common very fine tubular pores; few prominent and common distinct pressure cutans on faces of peds; 35 percent strongly cemented, flat pan fragments; 15 percent gravel and 5 percent cobbles; secondary carbonates segregated as few fine filaments or threads; noneffervescent matrix and strongly effervescent filaments; neutral (pH 7.2); abrupt wavy boundary. (0 to 10 cm thick)

2Bqkm--48 to 152 cm; cemented material; 1 to 2 mm thick laminar cap over matrix indurated by opaline silica; strong silica cementation with 1 to 2 millimeters thick discontinuous laminar cap lining fractures in lower part; violently effervescent.

TYPE LOCATION: Mineral County, Nevada; on the Toiyabe National Forest about 3 miles west of Aurora; approximately 700 feet east and 2,500 feet north of the southwest corner of section 14, T. 5 N., R. 27 E.; USGS Aurora 7.5 minute topographic quadrangle; latitude 38 degrees 17 minutes 27 seconds N and longitude 118 degrees 56 minutes 40 seconds W; WGS84 Decimal Degrees 38.2908333 latitude, -118.9444444 longitude.

RANGE IN CHARACTERISTICS:
Soil moisture: Usually moist in winter, spring, and early summer; dry summer and fall, but intermittently moist in some part above the moisture control section due to summer convection storms; Dry in all parts more than 45 consecutive days following the summer solstice; aridic moisture regime that borders on xeric.
Mean annual soil temperature: 7 to 8 degrees C.
Mollic epipedon thickness: 18 to 25 cm, includes the BAt horizon.
Depth to base of argillic horizon: 36 to 50 cm.
Depth to duripan: 36 to 50 cm.
Depth to bedrock: More than 150 cm.
Other features: An abrupt horizon boundary is normally present between the BAt horizon and the Bt horizon accompanied by an increase in clay content of more than 15 percent.

Particle-size control section - Clay content: 35 to 50 percent.
Rock fragments: 0 to 25 percent, dominantly gravel. Lithology of fragments are volcanic rocks such as basalt or strongly cemented to indurated detached duripan fragments.

A horizon
Chroma: 2 or 3, dry or moist.
Clay content: 5 to 15 percent.
Organic matter content: 1 to 3 percent.
Volcanic glass content: 30 to 75 percent in coarse silt through fine sand fractions.

BAt horizon
Chroma: 2 or 3, dry or moist.
Clay content: 18 to 27 percent.
Organic matter content: 1 or 2 percent.
Volcanic glass content: 30 to 75 percent in coarse silt through fine sand fractions.

2Bt horizon
Value: 5 or 6 dry, 3 or 4 moist.
Texture: Clay or gravelly clay loam.
Reaction: Neutral or slightly alkaline.
Other features: Sodium adsorption ratio is less than 5 in this horizon.

2Btqk horizon (when present)
Texture: Gravelly clay loam or very gravelly clay loam.
Clay content: 35 to 40 percent.
Rock fragments: 15 to 60 percent, mainly gravel.

2Bqkm horizon
Cementation: 1 to 4 mm thick continuous laminar cap of silica on upper surface of indurated matrix; strongly silica cemented plates with discontinuous 1 to 2 mm thick laminar cap lining fractures below.

COMPETING SERIES: This is the Moonbeam series. Moonbeam soils have lithic contacts at depths between 50 and 100 cm from the soil surface and are not intermittently moist in the upper horizons during summer months.

GEOGRAPHIC SETTING: Mopana soils are on plateaus. They typically occur on summit positions. These soils formed in eolian volcanic ash over residuum derived from basalt. The probable sources of the volcanic ash are the Mono Craters and Long Valley Caldera in eastern California. Slopes are 0 to 15 percent. Elevations range from 2,195 to 2,700 meters. The climate is semiarid with cold, moist winters and warm, dry summers. The mean annual precipitation is 300 to 410 mm, the mean annual temperature is 5 to 7 degrees C., and the frost-free period is 30 to 100 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Borealis and Nire soils. Borealis soils are fine, moderately deep to indurated duripans, and have ochric epipedons. Nire soils are very deep and have cryic temperature regime.

DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY: Well drained; very high surface runoff; very slow permeability; moderately low saturated hydraulic conductivity.

USE AND VEGETATION: Mopana soils are used for livestock grazing and wildlife habitat. The present vegetation is mainly low sagebrush, prairie junegrass, Thurber's needlegrass, Sandberg's bluegrass, and Douglas rabbitbrush.

DISTRIBUTION AND EXTENT: Western Nevada and eastern California. These soils are not extensive. MLRA 26.

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

SERIES ESTABLISHED: Mineral County Area, Nevada, 1985.

REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - The zone from the soil surface to 20 cm (A and BAt horizons).
Vitrandic intergrade feature - The zone from the soil surface to 20 cm (A and BAt horizons).
Argillic horizon - The zone from 10 to 48 cm (BAt, 2Bt, and 2Btqk horizons).
Identifiable secondary carbonates - The zone from 43 to 152 cm (2Btqk and 2Bqkm horizons).
Duripan - The zone from 48 to 152 cm (2Bqkm horizon).
Particle-size control section - The zone from 10 to 48 cm (BAt, 2Bt, and 2Btqk horizons).

The revision in March 2001 updated the taxonomic class from Clayey, smectitic, frigid, shallow Abruptic Aridic Durixerolls, designated the 10 to 20 cm zone as part of the argillic horizon, quantified the volcanic glass content in the upper horizons, and corrected the geographic coordinates of the type location. Volcanic glass content estimated from laboratory data on nearby pedons in Mineral County.

ADDITIONAL DATA: Volcanic glass content determined locally by optical grain count with a polarizing petrographic microscope.
User Pedon ID: 2007NV021094.

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National Cooperative Soil Survey
U.S.A.