LOCATION BIGMOW                  OR

Tentative Series
Rev. JRD/DAL/KMS
02/2013

BIGMOW SERIES

The Bigmow series consists of deep and very deep, well drained soils that formed in residuum and colluvium from rhyolite and sedimentary rock with an influence of volcanic ash in the upper part. Slopes are 1 to 70 percent. The mean annual temperature is about 42 degrees F. The mean annual precipitation is about 23 inches.

TAXONOMIC CLASS: Clayey-skeletal, smectitic, frigid Vertic Palexerolls

TYPICAL PEDON: Bigmow gravelly ashy sandy loam - forested. (Colors are for dry soil unless otherwise noted.)

Oi--0 to 0.5 inches; slightly decomposed sage twigs, and leaves. (0.5 to 3 inches thick)

A1--0.5 to 2 inches; dark brown (10YR 3/3) gravelly ashy sandy loam, very dark brown (10YR 2/2) moist; moderate thin platy structure; soft, friable, slightly sticky and slightly plastic; many very fine and fine roots; many very fine vesicular pores; 20 percent gravel; slightly acid (pH 6.4); abrupt smooth boundary. (1 to 3 inches thick)

A2--2 to 5 inches; dark brown (10YR 3/3) gravelly ashy sandy loam, very dark brown (10YR 2/2) moist; moderate thin and medium platy structure; soft, friable, slightly sticky and slightly plastic; many very fine, fine and medium roots; many very fine tubular and vesicular pores; 25 percent gravel; moderately acid (pH 6.0); abrupt smooth boundary. (2 to 4 inches thick)

AB--5 to 9 inches; dark brown (10YR 3/3) very stony ashy sandy clay loam, very dark brown (10YR 2/2) moist; moderate medium platy structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine, fine and medium roots; many very fine tubular pores; 25 percent gravel, 10 percent cobbles and 15 percent stones; slightly acid (pH 6.2); abrupt smooth boundary. (the combined thickness of the A and A/B horizons is 7 to 10 inches)

2Bt1--9 to 17 inches; dark brown (10YR 3/3) gravelly clay, very dark brown (10YR 2/2) moist; moderate fine and medium subangular blocky structure; slightly hard, friable, slightly sticky and moderately plastic; few very fine, fine and medium roots, common coarse roots; common very fine and fine tubular pores; few faint clay films on peds and rock fragments, common clay bridging of sand grains; 30 percent gravel; slightly acid (pH 6.2); clear wavy boundary. (6 to 20 inches thick)

2Bt2--17 to 25 inches; dark yellowish brown (10YR 4/4) extremely cobbly sandy clay, dark yellowish brown (10YR 3/4) moist; hard, firm, moderately sticky and moderately plastic; common very fine, fine and medium roots; common very fine and fine tubular pores; common distinct clay films on ped faces and rock fragments; 20 percent gravel, 30 percent cobbles, and 20 percent stones; moderately acid (pH 5.8); clear wavy boundary. (10 to 20 inches thick)

2Bt3--25 to 50 inches; dark yellowish brown (10YR 4/4) extremely cobbly sandy clay, dark yellowish brown (10YR 3/4) moist; hard, firm, moderately sticky and moderately plastic; few very fine, fine and medium roots; common very fine and fine tubular pores; many distinct clay films on ped faces, lining pores and on rock fragments; 20 percent gravel, 40 percent cobbles, and 20 percent stones; slightly acid (pH 6.4); clear wavy boundary. (10 to 20 inches thick)

2Cr--50 inches; weathered sedimentary rock

TYPE LOCATION: Harney County, Oregon, on western upper slope of Big Mowich Mountain
Section 2, T. 19 S, R. 26 E.

Latitude: 43 degrees, 57 minutes, 19 seconds
Longitude: 119 degrees 35 minutes 41 seconds
NAD83

Northing: 4,870,179 meters
Easting: 291,812 meters
Zone 11
NAD83

RANGE IN CHARACTERISTICS:
Mean annual soil temperature - 37 to 41 degrees F.
Mean summer soil temperature - 44 to 49 degrees F.
Mean winter soil temperature - 32 to 36 degrees F.
Soil moisture - dry 45 to 60 consecutive days in summer and early fall
Particle-size control section clay content (weighted average) - 35 to 55 percent
Particle-size control section rock fragment content (weighted average) - 35 to 85 percent Thickness of mollic epipedon - 10 to 20 inches
Depth to bedrock - greater than 40 inches
Thickness of volcanic ash influence - 7 to 10 inches
Estimated properties of volcanic ash influenced layers:
Acid oxalate extractable Al+1/2Fe - 0.4 to 1.0 percent
Volcanic glass content - 5 to 20 percent

A horizons
Value - 2 or 3 moist, 3 to 5 dry
Chroma - 2 or 3 moist, 2 to 4 dry
Fine-earth texture - ashy sandy loam, or ashy loamy sand
Clay content - 10 to 20 percent
Gravel content - 5 to 30 percent
Cobbles content - 0 to 5 percent
Reaction - moderately acid or slightly acid

AB horizon (when present)
Value - 2 or 3 moist, 3 to 5 dry
Chroma - 2 or 3 moist, 2 to 4 dry
Fine-earth texture- ashy sandy clay loam
Clay content - 20 to 30 percent
Gravel content - 15 to 30 percent
Cobbles content - 10 to 20 percent
Stone content - 0 to 20 percent

2Bt horizons
Value - 2 or 3 moist, 3 to 5 dry
Chroma - 2 to 4 moist, 3 or 4 dry
Fine-earth texture - clay or sandy clay
Clay content - 35 to 55 percent
Gravel content - 20 to 40 percent
Cobbles content - 0 to 40 percent
Stone content - 0 to 20 percent
Reaction - moderately acid to neutral

COMPETING SERIES: These are the Diffin and Yawkey series.. Diffin soils lack the vitrandic properties in the upper 7 to 10 inches of the solum. Yawkey soils have a mollic epipedon over 20 inches thick.

GEOGRAPHIC SETTING: The Bigmow soils are on uplands at elevations of 3,500 to 5,200 feet. Slope gradients are 1 to 70 percent. These soils formed in residuum and colluvium from rhyolitic tuffs and marine sediments with an influence of volcanic ash in the surface. The mean annual precipitation is 16 to 26 inches, mean annual temperature is 40 to 45 degrees F, mean summer temperature is 58 to 62 degrees F, and the mean winter temperature is 27 to 32 degrees F. The frost-free period is 20 to 90 days.

GEOGRAPHICALLY ASSOCIATED SOILS:
Volspring - on sideslopes and benches; very deep; with ash mantle 14 to 20 inches thick.
Moeo - on mountain sideslopes and benches; shallow to bedrock.
Laycock - on hillsides, shallow to bedrock.
Burntcabin - in swales, drainageways and toeslopes; fine-loamy; very deep.
Forbord - on sideslopes and benches of hills and mountains; fine-loamy.

DRAINAGE AND PERMEABILITY: Well-drained; medium to very rapid runoff; slow permeability.

USE AND VEGETATION: Mainly used for timber production with limited summer range. Other uses are wildlife, recreation and water supply purposes. Native plants are ponderosa pine, western juniper, mountain big sage, whorteleaf snowberry, bluebunch wheatgrass, mountain brome and Wheeler bluegrass. This series is characterized by what is called the moist and dry ponderosa pine forest plant association groups.

DISTRIBUTION AND EXTENT: MLRA: 10 Central Oregon. This series is not extensive.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon

SERIES PROPOSED: Harney County, Ochoco National Forest, 2010

REMARKS: Diagnostic horizons and other features:
Mollic epipedon - 0.5 to 17 inches (A1, A2, AB, and 2Bt1 horizons)
Argillic horizon - 5 to 50 inches (AB, 2Bt1, 2Bt2, and 2Bt3 horizons)
Vitrandic feature - 0.5 to 9 inches (A1, A2, and AB horizons)
Pale great group - abrupt textural change at 17 inches (occurs between AB and 2Bt1 horizons)
Vertic subgroup - the calculated LE is over 6.0 centimeters within the upper meter

This soil is assumed to have a base saturation of more than 75 percent by sum of bases throughout the solum

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National Cooperative Soil Survey
U.S.A.