LOCATION SOUTHMOUNT IDEstablished Series
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 45 inches and moist below.)
Oi--1 to 0 inches; partly decomposed needles and twigs. (1 to 3 inches thick)
A--0 to 5 inches; 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 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. (5 to 15 inches thick)
Bt1--5 to 13 inches; dark 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 plastic; many very fine, fine and medium, few coarse roots; common fine and very fine tubular pores; many thin clay films on faces of peds and lining pores; 10 percent gravel, 10 percent cobbles; moderately acid (pH 6.0); clear smooth boundary. (7 to 19 inches thick)
Bt2--13 to 18 inches; brown (10YR 4/3) gravelly clay loam, dark brown (10YR 3/3) moist; moderate fine and medium subangular blocky structure; hard, friable, sticky and plastic; common very fine, fine and medium, few coarse roots; common fine and very fine tubular pores; many moderately thick clay films on faces of peds and lining pores; 10 percent gravel, 5 percent cobbles; strongly acid (pH 5.5); clear wavy boundary. (5 to 17 inches thick)
2Bt3--18 to 42 inches; 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 thin clay films on faces of peds; trace manganese concretions; 20 percent gravel; strongly acid (pH 5.5); gradual irregular boundary. (0 to 24 inches thick)
2C--42 to 60 inches; 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; 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; 1,500 feet east and 1,100 feet north of the southwest corner of sec. 6, T.8 S., R.4 W.
RANGE IN CHARACTERISTICS:
Average annual soil temperature - 36 to 40 degrees F.
Average summer soil temperature - 48 to 52 degrees F.
Mollic epipedon thickness - 16 to 38 inches
Particle-size control section - 24 to 32 percent clay; 0 to 20 percent rock fragments
Depth to mottles - 18 to 40 inches
A horizon
Value - 3 or 4 dry
Chroma - 1 through 3 dry or moist
Rock fragments - 0 to 15 percent
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 40 inches
COMPETING SERIES: These are the Bachus, Benteen, Cambern, Clayburn, Crystalbutte, Davtone, Decross, Dehana (T), Demast, Dranyon, Echemoor, Gordo, Hagenbarth, Harmehl, Millerlake, Senchert, Squawval, Stubbs, Thulepah, Vadnais, and Winu series. The Bachus, Benteen, Cambern, Echemoor, Harmehl, Senchert, Squawval, Stubbs, Vadnais, and Winu soils are 20 to 40 inches to lithic or paralithic contact. Clayburn soils have a mean summer temperature of about 58 degrees F, lack O horizons and the depth to the upper boundary of the argillic is 15 to 24 inches. 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 55 to 59 degrees F, 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 20 inches to the upper part of the Bt horizon. Dranyon soils are well drained and lack mottles above 40 inches. Gordo soils have hue redder than 7.5YR in the control section. Hagenbarth soils have an average annual soil temperature of 52 to 58 degrees F. Thulepah soils have an average summer soil temperature of 43 to 47 degrees F, lack 0 horizons and have 12 to 16 inches 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 5,800 to 7,400 feet. 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 22 to 36 inches most of which is snow. The average annual temperature ranges from 35 to 38 degrees F. 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 OFFICE RESPONSIBLE: Reno, Nevada
SERIES ESTABLISHED: Owyhee County Area, Idaho 1992.
REMARKS: Diagnostic horizons and other features recognized in this pedon:
Mollic epipedon - zone 0 to 18 inches (A, Bt1, and Bt2)
Argillic horizon - zone 5 to 42 inches (Bt1, Bt2, and 2Bt3)
Particle-size control section - zone 5 to 25 inches (Bt1, Bt2, and upper part of 2Bt3)