LOCATION SILVERCITY MTEstablished Series
TAXONOMIC CLASS: Loamy-skeletal over sandy or sandy-skeletal, mixed, superactive, frigid Typic Argiustolls
TYPICAL PEDON: Silvercity gravelly loam, in rangeland (colors are for dry soils unless otherwise noted).
A--0 to 6 inches; dark grayish brown (10YR 4/2) gravelly loam, very dark brown (10YR 2/2) moist; moderate very thin platy structure parting to moderate fine granular; soft, very friable, slightly sticky and slightly plastic; many very fine roots; 15 percent pebbles; neutral (pH 7.2); clear smooth boundary. (5 to 8 inches thick)
Bt1--6 to 10 inches; brown (10YR 5/3) gravelly clay loam, dark brown (10YR 3/3) moist; moderate medium prismatic structure parting to moderate medium subangular blocky; slightly hard, friable, moderately sticky and slightly plastic; common very fine roots; many very fine tubular and interstitial pores; common faint very dark grayish brown (10YR 3/2) clay films on faces of peds; 20 percent pebbles and 5 percent cobbles; neutral (pH 7.2); clear smooth boundary. (3 to 6 inches thick)
Bt2--10 to 24 inches; brown (10YR 5/3) very gravelly clay loam, brown (10YR 4/3) moist; moderate medium subangular blocky structure; hard, firm, moderately sticky and slightly plastic; common very fine roots; many very fine tubular and interstitial pores; many faint dark brown (10YR 3/3) clay films on faces of peds and on coarse fragments; 35 percent pebbles and 15 percent cobbles; slightly alkaline (pH 7.4); clear smooth boundary. (12 to 25 inches thick)
2Bk--24 to 60 inches; light brownish gray (10YR 6/2) extremely gravelly loamy sand; dark grayish brown (10YR 4/2) moist; single grain; loose; nonsticky and nonplastic; few very fine roots in upper part; 40 percent pebbles and 25 percent cobbles; common distinct lime casts on underside of larger fragments; lime disseminated; strongly effervescent; slightly alkaline (pH 7.6).
TYPE LOCATION: Lewis and Clark County, Montana; 1,980 feet west and 1,500 feet north of the SE corner of sec. 21, T. 14 N., R. 9 W.
RANGE IN CHARACTERISTICS:
Soil temperature - 40 to 45 degrees F.
Moisture control section - between 4 and 12 inches.
Mollic epipedon thickness - 7 to 15 inches.
Depth to sandy skeletal material - 20 to 40 inches.
A horizon - Value: 2 or 3 moist
Chroma: 1 or 2
Clay content: 15 to 25 percent
Rock fragments: 15 to 35 percent--0 to 5 percent cobbles, 15 to 30 percent pebbles
Reaction: pH 6.6 to 7.3
Bt1 horizon - Value: 4 or 5 dry, 3 or 4 moist
Chroma: 2 or 3
Texture: loam or clay loam
Clay content: 25 to 35 percent
Rock fragments: 25 to 60 percent--5 to 10 percent cobbles, 20 to 50 percent pebbles
Reaction: pH 6.6 to 7.3
Bt2 horizon - Value: 5 or 6 dry, 4 or 5 moist
Chroma: 3, 4, or 5
Texture: loam or clay loam
Clay content: 25 to 35 percent
Rock fragments: 35 to 60 percent--5 to 10 percent cobbles, 30 to 50 percent pebbles
Reaction: pH 6.6 to 7.8
2Bk horizon - Hue: 10YR or 2.5Y
Value: 5 or 6 dry, 4 or 6 moist
Chroma: 2 or 3
Texture: loamy sand or sand
Clay content: 0 to 5 percent
Rock fragments: 60 to 80 percent--10 to 20 percent cobbles, 50 to 60 percent pebbles
Calcium carbonate equivalent: 5 to 15 percent
Reaction: pH 7.4 to 8.4
COMPETING SERIES:
Beaverton (MT) - 10 to 20 inches to sandy-skeletal material.
Harol (UT) - does not have a 2Bk horizon.
Shirttail (SD) - has a lithic contact at 40 to 60 inches.
GEOGRAPHIC SETTING:
Landform - stream terraces and dissected alluvial fans in mountain valleys.
Elevation - 4,000 to 5,000 feet.
Slope - 0 to 4 percent.
Parent material - alluvium containing a high amount of coarse fragments.
Climate - long, cold winters; moist springs; short summers.
Mean annual precipitation - 18 to 22 inches, most of which falls as snow and spring rain.
Mean annual air temperature - 38 to 43 degrees F.
Frost-free period - 70 to 80 days.
DRAINAGE AND PERMEABILITY: Well drained; moderate permeability in the loamy-skeletal material and rapid in the sandy-skeletal material.
USE AND VEGETATION: Silvercity soils are used for rangeland and irrigated cropland. The potential native vegetation is mainly rough fescue, Columbia needlegrass, Richardson needlegrass, Idaho fescue, forbs, and shrubs.
DISTRIBUTION AND EXTENT: Silvercity soils are of limited extent in mountain valleys of western Montana.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Lewis and Clark County Area, Montana, 1991; proposed in Lewis and Clark County, Montana, 1990. Silvercity is a place name.
REMARKS: Soil interpretation record: MT1257. Diagnostic horizons and features recognized in this pedon are: a mollic epipedon from the soil surface to a depth of 10 inches (A and Bt1 horizons); an argillic horizon from 6 to 24 inches (Bt1 and B2t horizons); a sandy-skeletal 2Bk horizon from 24 to 60 inches; and a particle-size control section from the top of the argillic horizon to a depth of 40 inches (Bt1, Bt2, and 2Bk horizons). Silvercity soils have a frigid temperature regime and an ustic moisture regime.