LOCATION OVERWHICH MT
Established Series
Rev. EMR/JMS/RJS
07/2013
OVERWHICH SERIES
The Overwhich series consists of very deep, somewhat poorly drained soils that formed in alluvium or outwash. These soils are on stream terraces, outwash fans, and flood plains. Slopes are 0 to 8 percent. Mean annual precipitation is about 330 mm. Mean annual air temperature is about 6 degrees C.
TAXONOMIC CLASS: Coarse-loamy over sandy or sandy-skeletal, mixed, superactive, frigid Oxyaquic Haplustolls
TYPICAL PEDON: Overwhich loam, in rangeland on a 1 percent slope at 1,047 meters elevation (colors are for dry soil unless otherwise noted).
A--0 to 28 cm; grayish brown (10YR 5/2) loam, very dark brown (10YR 2/2) moist; moderate medium granular structure; soft, very friable, slightly sticky and slightly plastic; many very fine and common fine roots; many very fine and fine irregular and tubular pores; slightly alkaline (pH 7.8); slightly effervescent; clear smooth boundary. (25 to 36 cm thick)
Bw--28 to 43 cm; light brownish gray (10YR 6/2) loam, very dark grayish brown (10YR 3/2) moist; weak fine subangular blocky structure; soft, very friable, slightly sticky and slightly plastic; common very fine and few fine roots; many very fine and fine irregular and tubular pores; slightly alkaline (pH 7.8); slightly effervescent; gradual smooth boundary. (15 to 48 cm thick)
C1--43 to 71 cm; light brownish gray (2.5Y 6/2) fine sandy loam, dark grayish brown (10YR 4/2) moist; massive; soft, very friable, nonsticky and nonplastic; few very fine and fine roots; common fine interstitial pores; 5 percent medium distinct yellowish brown (10YR 5/4) redox concentrations; slightly alkaline (pH 7.6); gradual wavy boundary.
C2--71 to 84 cm; light gray (2.5Y 7/2) fine sandy loam, grayish brown (2.5Y 5/2) moist; massive; soft, very friable, nonsticky and nonplastic; few very fine and fine roots; common fine interstitial pores; 10 percent medium prominent yellowish brown (10YR 5/6) redox concentrations; 5 percent gravel; slightly alkaline (pH 7.6); clear wavy boundary. (combined thickness of C horizons 18 to 58 to cm thick)
2C3--84 to 152 cm; light gray (2.5Y 7/2) very gravelly loamy sand, grayish brown (2.5Y 5/2) moist; single grain; loose, nonsticky and nonplastic; few very fine roots; common fine interstitial pores; 5 percent medium prominent yellowish brown (10YR 5/6) redox concentrations; 50 percent gravel, 5 percent cobbles; slightly alkaline (pH 7.4).
TYPE LOCATION: Corvallis topographic quadrangle, Ravalli County, Montana; 585 meters north and 750 meters west of the SE corner of section 21, T. 7 N., R. 20 W. UTM Zone 11: 722942e, 5136667n, NAD 83.
RANGE IN CHARACTERISTICS:
Mean annual soil temperature - 5 to 8 degrees C
Mollic epipedon thickness - 25 to 36 cm
Depth to seasonal high water table - 60 to 100 cm for extended periods during late spring or early summer
Depth to lithologic discontinuity - 58 to 98 cm
A horizon
Value: 4 or 5 dry; 2 or 3 moist
Chroma: 1 or 2 dry or moist
Texture: loam or silt loam
Clay content: 12 to 26 percent
Rock fragments: 0 to 15 percent--0 to 10 percent gravel; 0 to 5 percent cobbles and stones
Reaction: pH 6.6 to 7.8
Bw horizon
Value: 5, 6, or 7 dry; 3, 4, or 5 moist
Chroma: 2 or 3 dry or moist
Texture: loam or fine sandy loam
Clay content: 12 to 20 percent
Rock fragments: 0 to 15 percent--0 to 10 percent gravel; 0 to 5 percent cobbles and stones
Reaction: pH 6.6 to 8.0
C1 and C2 horizons
Hue: 10YR or 2.5Y
Value: 6 or 7 dry; 4 or 5 moist
Chroma: 2 or 3 dry or moist
Texture: fine sandy loam or loam
Clay content: 10 to 18 percent
Rock fragments: 0 to 35 percent--0 to 20 percent gravel; 0 to 15 percent cobbles and stones
Reaction: pH 6.6 to 7.8
2C horizon
Hue: 10YR or 2.5Y
Value: 6 or 7 dry; 4 or 5 moist
Chroma: 2 or 3 dry or moist
Texture: loamy sand, loamy coarse sand, or coarse sand
Clay content: 0 to 10 percent
Rock fragments: 35 to 80 percent--35 to 70 percent gravel; 0 to 20 percent cobbles and stones
Reaction: pH 6.1 to 7.8
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING:
Landform - stream terraces, outwash fans, and flood plains
Elevation - 980 to 1,500 meters
Slope - 0 to 8 percent
Parent material - alluvium or outwash
Climate - long, cold winters; moist springs; warm summers
Mean annual precipitation - 305 to 432 mm
Mean annual air temperature - 4 to 7 degrees C
Frost-free period - 80 to 115 days
GEOGRAPHICALLY ASSOCIATED SOILS: None listed.
DRAINAGE AND PERMEABILITY: Somewhat poorly drained; moderate and moderately rapid permeability to 84 cm and rapid permeability below.
USE AND VEGETATION: These soils are used for irrigated and dryland pasture, irrigated hay, rangeland, and wildlife habitat. Vegetation is chiefly mixed grasses, small grains, and minor acreages of other crops grown under irrigation.
DISTRIBUTION AND EXTENT: The Overwhich series is of small extent in the intermountain valleys of southwestern Montana. MLRA 44A.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana.
SERIES ESTABLISHED: Bitterroot Valley Area, Montana, 2013; proposed in Ravalli County, Montana, 2006.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - from the surface to 28 cm (A horizon)
Cambic horizon - from 28 to 43 cm (Bw horizon)
Redox concentrations - from 43 to 152 cm (C1, C2, and 2C3 horizons)
Lithologic Discontinuity - at 84 cm (2C3 horizon)
Particle-size control section - from 25 to 100 cm (part of the A, Bw, C1, C2, and part of the 2C3 horizons
Overwhich soils have a frigid temperature regime, an ustic moisture regime, and an oxyaquic moisture subclass.
National Cooperative Soil Survey
U.S.A.