LOCATION SOUTHMOUNT              ID

Established Series
Rev. DH/ALH/CLM
12/2022

SOUTHMOUNT SERIES

The Southmount series consists of very deep, moderately well drained soils with moderately slow permeability that formed in slope alluvium and colluvium from basalt. Southmount soils are on north and east-facing sideslopes and toeslopes of mountains. Slopes range from 5 to 40 percent. Average annual precipitation is about 710 mm and average annual temperature is about 3.3 degrees C.

TAXONOMIC CLASS: Fine-loamy, mixed, superactive Pachic Argicryolls

TYPIC PEDON: Southmount silt loam -- on a northeast-facing slightly convex slope of 8 percent, under Douglas fir woodland, at 5,840 feet elevation. (Colors are for air dry soil unless otherwise stated. When described on August 17, l983, the soil was slightly moist from 0 to 117 cm and moist below.)

Oi--0 to 3 cm; partly decomposed needles and twigs. (3 to 8 cm thick)

A--3 to 16 cm; dark brown (10YR 3/3) silt loam, very dark brown (10YR 2/2) moist; weak fine and medium subangular blocky structure parting to moderate fine granular; slightly hard, very friable, slightly sticky and slightly plastic; common fine and very fine, few medium and coarse roots; common fine and very fine vesicular and interstitial pores; 10 percent gravel; neutral (pH 6.7); clear wavy boundary. (13 to 38 cm thick)

Bt1--16 to 36 cm; brown (10YR 4/3) cobbly silt loam, very dark brown (10YR 2/2) moist; moderate fine and medium subangular blocky structure; slightly hard, very friable, slightly sticky and moderately plastic; many very fine, fine and medium, few coarse roots; common fine and very fine tubular pores; many faint clay films on faces of peds and lining pores; 10 percent gravel, 10 percent cobbles; moderately acid (pH 6.0); clear smooth boundary. (18 to 48 cm thick)

Bt2--36 to 49 cm; brown (10YR 4/3) gravelly clay loam, dark brown (10YR 3/3) moist; moderate fine and medium subangular blocky structure; hard, friable, moderately sticky and moderately plastic; common very fine, fine and medium, few coarse roots; common fine and very fine tubular pores; many distinct clay films on faces of peds and lining pores; 10 percent gravel, 5 percent cobbles; strongly acid (pH 5.5); clear wavy boundary. (13 to 43 cm thick)

2Bt--49 to 110 cm; brownish yellow (10YR 6/6) gravelly clay loam, dark yellowish brown (10YR 4/6) moist, with few fine distinct mottles of strong brown (7.5YR 5/6); moderate medium angular blocky structure; hard, friable, slightly sticky and slightly plastic; few fine and very fine roots; common fine and very fine tubular pores; common faint clay films on faces of peds; trace manganese concretions; 20 percent gravel; strongly acid (pH 5.5); gradual irregular boundary. (0 to 61 cm thick)

2C--110 to 155 cm; light yellowish brown (2.5Y 6/4) sandy loam, olive brown (2.5Y 4/4) moist, with few medium prominent mottles of yellow (2.5Y 7/6); massive; very hard, friable, nonsticky and nonplastic; few fine and very fine tubular pores; trace manganese concretions; 5 percent gravel; strongly acid (pH 5.2).

TYPE LOCATION: Owyhee County, Idaho; about 18 miles south and 6 miles west of Silver City; 2,000 feet east and 1,100 feet north of the southwest corner of sec. 6, T. 8 S., R. 4 W.; USGS Combination Ridge 7.5 minute topographic quadrangle; latitude 42 degrees 45 minutes 15 seconds N and longitude 116 degrees 51 minutes 27 seconds W; WGS84 Decimal Degrees 42.7541667 latitude, -116.8575000 longitude.

RANGE IN CHARACTERISTICS:

Average annual soil temperature - 2.2 to 4.4 degrees C.
Average summer soil temperature - 8.9 to 11.1 degrees C.
Typic udic moisture regime.
Mollic epipedon thickness - 41 to 97 cm.
Particle-size control section - 24 to 32 percent clay; 0 to 20 percent rock fragments
Depth to mottles - 46 to 100 cm.

A horizon
Value - 3 or 4 dry
Chroma - 1 through 3 dry or moist
Reaction (pH) - slightly acid or neutral

Bt1 horizon
Value - 4 or 5 dry, 2 or 3 moist
Chroma - 2 or 3 dry or moist
Texture - CB-SIL, L, or SIL
Rock fragments - 0 to 20 percent
Reaction (pH) - moderately or slightly acid

Bt2 horizon
Value - 4 or 5 dry, 3 or 4 moist
Chroma - 3 or 4 dry or moist
Texture - CB-CL or CL
Rock fragments - 0 to 20 percent
Reaction (pH) - strongly through slightly acid
Other features - moderately coarse textured, strongly or moderately acid C horizons commonly occur below 100 cm.

COMPETING SERIES: These are the Bachus, Benteen, Cambern, Clayburn, Crystalbutte, Davtone, Decross, Dehana, Demast, Dranyon, Echemoor, Gordo, Hagenbarth, Harmehl, Millerlake, Senchert, Poodle, Stubbs, Thulepah, Vadnais, and Winu series. The Bachus, Benteen, Cambern, Echemoor, Harmehl, Senchert, Poodle, Stubbs, Vadnais, and Winu soils are 50 to 100 cm to lithic or paralithic contact. Clayburn soils have a mean summer temperature of about 14.4 degrees C., lack O horizons and the depth to the upper boundary of the argillic is 38 to 61 cm. Crystalbutte, Dehana, and Demast soils have more than 20 percent rock fragments in the control section. Davtone soils have a mean summer soil temperature of 12.7 to 15.0 degrees C., lack O horizons and have hues of 5YR and redder in the Bt horizon. Decross and Millerlake soils have Bk horizons. Demast soils are more than 50 cm to the upper part of the Bt horizon. Dranyon soils are well drained and lack mottles above 100 cm. Gordo soils have hue redder than 7.5YR in the control section. Hagenbarth soils have an average annual soil temperature of 11.1 to 14.4 degrees C. Thulepah soils have an average summer soil temperature of 6.1 to 8.3 degrees C., lack 0 horizons and have 300 to 410 mm of precipitation.

GEOGRAPHIC SETTING: Southmount soils are strongly sloping to steep on north and east facing, dominantly concave, sideslopes and toeslopes of mountains at elevations of 1,770 to 2,260 meters. Slopes range from 5 to 40 percent. These soils formed in slope alluvium and colluvium from basalt. The climate is cold and moist in winter and warm and dry in summer. The average annual precipitation is 560 to 910 mm, most of which is snow. The average annual temperature ranges from 2.2 to 3.3 degrees C. The frost-free period is 30 to 60 days.

GEOGRAPHICALLY ASSOCIATED SOILS: This is the Booneville series. Booneville soils have more than 35 percent coarse fragments in the control section and are on upper slopes.

DRAINAGE AND PERMEABILITY: Moderately well drained; slow to rapid runoff; moderately slow permeability. The soil is saturated at depths of 3.5 to 5.0 feet for brief periods in the spring.

USES AND VEGETATION: Southmount soils are used mainly for woodland and wildlife habitat. The dominant natural vegetation is Douglas fir, mountain snowberry, Oregon grape, and elk sedge. Quaking aspen is a common seral species.

DISTRIBUTION AND EXTENT: Southmount soils are of small extent in southwestern Idaho. MLRA 25.

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 from 3 to 49 cm (A, Bt1 and Bt2 horizons).
Argillic horizon - The zone from 16 to 110 cm (Bt1, Bt2 and 2Bt3 horizons).

Particle-size control section - The zone from 16 to 66 cm (Bt1, Bt2 and upper part of 2Bt3 horizons).

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National Cooperative Soil Survey
U.S.A.