LOCATION TWINBRIDGE              OR

Established Series
Rev. RLW/KMS
11/2018

TWINBRIDGE SERIES

Landscape--mountains
Landform--mountain slopes
Slope--15 to 60 percent
Parent material--colluvium and residuum derived from limestone with a minor influence of volcanic ash in the upper part
Mean annual precipitation--about 1510 mm
Mean annual air temperature--about 6 degrees C
Depth class--shallow to lithic bedrock
Drainage class--well drained
Soil moisture regime--xeric
Soil temperature regime--frigid
Soil moisture subclass--typic

TAXONOMIC CLASS: Loamy-skeletal, isotic, frigid Lithic Haploxerepts

TYPICAL PEDON: Twinbridge extremely cobbly ashy silt loam, forested, on a 30-percent slope at an elevation of 2062 m

A--0 to 13 cm; extremely stony ashy silt loam, dark yellowish brown (10YR 4/4) dry, dark yellowish brown (10YR 3/4) moist; weak very fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine, fine, and medium roots throughout; common fine tubular and irregular pores; 40 percent gravel, 25 percent cobbles, and 20 percent stones; noneffervescent; moderately alkaline (pH 8.0); clear smooth boundary

2Bw--13 to 43 cm; extremely stony silt loam, dark yellowish brown (10YR 4/4) dry, dark yellowish brown (10YR 3/4) moist; moderate medium subangular blocky structure parting to weak fine subangular blocky; slightly hard, friable, slightly sticky and slightly plastic; common very fine, fine, and medium roots throughout; common fine and medium irregular pores and common fine tubular pores; 35 percent gravel, 25 percent cobbles, and 25 percent stones; moderately alkaline (pH 8.0); abrupt irregular boundary

2R--43 cm; fractured limestone

TYPE LOCATION: Baker County, Oregon; in the NW1/4SW1/4SW1/4 of section 5, T. 7 S., R. 45 E., latitude 44.9825149, longitude -117.2446890, datum WGS 84 (coordinates estimated from PLSS details)

RANGE IN CHARACTERISTICS:
Mean annual soil temperature--4 to 8 degrees C
Soil moisture--dry 60 to 90 days following summer solstice
Depth to lithic contact--25 to 50 cm
Thickness of layers influenced by volcanic ash--5 to 15 cm

Estimated properties of layers influenced by volcanic ash
*Ammonium oxalate extractable Al + 1/2 Fe--0.4 to 1.0 percent
*0.02- to 2.0-mm fraction--more than 30 percent
*Glass content in 0.02- to 2.0-mm fraction--5 to 15 percent

Particle-size control section
*Clay content--10 to 18 percent
*Total rock fragment content--more than 35 percent

A horizon
Fine-earth texture--ashy silt loam
Clay content--10 to 18 percent
Sand content--15 to 30 percent
Organic matter content--2 to 5 percent
Total rock fragment content--60 to 90 percent
Gravel content--20 to 60 percent
Cobble content--20 to 40 percent
Stone content--10 to 30 percent
Reaction--7.9 to 8.4

2Bw
Fine-earth texture--silt loam
Clay content--10 to 18 percent
Sand content--15 to 30 percent
Organic matter content--1 to 2 percent
Total rock fragment content--60 to 90 percent
Gravel content--20 to 60 percent
Cobble content--20 to 40 percent
Stone content--10 to 30 percent
Calcium carbonate content--0 to 5 percent
Reaction--7.9 to 8.4

COMPETING SERIES:
Powderriver, Vogel--volcanic ash influence more than 15 cm thick; meets vitrandic criteria

GEOGRAPHIC SETTING:
Elevation--1780 to 2210 m
Climate--cool, wet winters; hot, dry summers
Mean annual precipitation--1290 to 1650 mm
Mean annual air temperature--5 to 7 degrees C
Frost-free season--60 to 120 days

GEOGRAPHICALLY ASSOCIATED SOILS: None given

DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY:
Drainage class--well drained
Saturation during normal years--none
Flooding--none
Ponding--none
Saturated hydraulic conductivity (Ksat)--moderately high

USE AND VEGETATION:
Use--timber production, recreation, wildlife habitat
Potential native vegetation--ponderosa pine, common snowberry, bluebunch wheatgrass, Idaho fescue, common yarrow, Kentucky bluegrass, pinegrass, heartleaf arnica

DISTRIBUTION AND EXTENT: Eastern Oregon; MLRA 10; small extent

SOIL SURVEY REGIONAL OFFICE (SSRO) RESPONSIBLE: Portland, Oregon

SERIES ESTABLISHED: Wallowa-Whitman National Forest, Oregon; 2018

REMARKS:
Diagnostic horizons and other features recognized in this pedon
*Ochric epipedon
*Volcanic glass--zone from the surface to a depth of 13 cm
*Depth to lithologic discontinuity--43 cm
*Particle-size control section--zone from 25 to 43 cm

8/2017--The Twinbridge series is limited in extent, but it was proposed because of the unique limestone geology. The pedon was described by Bob Ottersberg in 1993.

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National Cooperative Soil Survey
U.S.A.