LOCATION MCDUFF OREstablished Series
TAXONOMIC CLASS: Fine, isotic, mesic Typic Haplohumults
TYPICAL PEDON: McDuff silty clay loam, forested. (Colors are for moist soil unless otherwise noted.)
Oi--0 to 1 inch; duff and litter, salal, fern leaves, and twigs.
A1--1 to 7 inches; very dark brown (10YR 2/2) silty clay loam, dark grayish brown (10YR 4/2) dry; strong fine granular structure; hard, firm, moderately sticky and moderately plastic; many very fine to medium roots; many very fine pores; strongly acid (pH 5.2); clear smooth boundary.
A2--7 to 12 inches; very dark grayish brown (10YR 3/2) silty clay loam, dark grayish brown (10YR 4/2) dry; moderate very fine subangular blocky and granular structure; hard, firm, very sticky and moderately plastic; many very fine to medium roots; many very fine pores; strongly acid (pH 5.2); clear smooth boundary. (Combined thickness of the A horizon is 3 to 17 inches).
BA--12 to 20 inches; dark brown (10YR 3/3) silty clay, brown (10YR 4/3) dry; moderate medium and fine subangular blocky structure; very hard, very firm, very sticky and very plastic; many very fine to medium roots; few very fine pores; very strongly acid (pH 4.7); clear wavy boundary. (0 to 12 inches thick)
Bt1--20 to 27 inches; dark brown (10YR 3/3) silty clay, brown (10YR 4/3) dry; moderate fine and medium subangular blocky structure; very hard, very firm, very sticky and very plastic; common very fine and fine roots; common very fine pores; few distinct clay films; very strongly acid (pH 4.7); clear wavy boundary.
Bt2--27 to 33 inches; dark yellowish brown (10YR 4/4) silty clay, strong brown (7.5YR 5/6) dry; moderate fine and medium subangular blocky structure; very hard, very firm, very sticky and very plastic; common very fine and fine roots; few very fine pores; common distinct clay films; few fine weathered siltstone fragments; very strongly acid (pH 4.6); clear wavy boundary. (Combined thickness of the Bt horizon is 5 to 17 inches)
BCt--33 to 39 inches; variegated strong brown (7.5YR 5/6) and pale brown (10YR 6/3) silty clay; moderate medium subangular blocky structure; very hard, firm, very sticky and very plastic; few very fine roots; few very fine pores; common distinct clay films; 30 percent fine weathered siltstone fragments; very strongly acid (pH 4.6); clear wavy boundary. (4 to 16 inches thick)
Cr--39 to 45 inches; partially weathered pale brown (10YR 6/3) siltstone bedrock; reddish brown (5YR 4/4) coatings on siltstone fragments.
TYPE LOCATION: Polk County, Oregon; about 0.5 mile east of Lincoln County line; SW1/4 SE1/4 section 6, T. 6 S., R. 8 W.; Midway, OR 7.5 minute USGS quadrangle; NAD 1927.
RANGE IN CHARACTERISTICS: The mean annual soil temperature is 47 to 56 degrees F. The soil is usually moist and is dry between depths of 4 and 12 inches for less than 45 consecutive days in the four-month period following the summer solstice in most years. The umbric epipedon is 20 to 30 inches thick and may include the upper part of the Bt horizon. The depth to bedrock is 20 to 40 inches. Content of rock fragments in the particle-size control section is 0 to 10 percent gravel, 0 to 25 percent paragravel, and 0 to 5 percent paracobbles. Reaction is very strongly acid or strongly acid.
The A horizon has hue of 10YR or 7.5YR, value of 2 or 3 moist, 4 or 5 dry, and chroma of 2 or 3 moist and dry. Texture is silty clay loam or clay loam in the upper part, and silty clay loam, clay loam, paragravelly silty clay loam or paragravelly clay loam in the lower part with 27 to 35 percent clay. It has 0 to 10 percent gravel, 0 to 5 percent cobbles, and 0 to 20 percent paragravel.
The Bt horizon has hue of 2.5Y, 10YR or 7.5YR, value of 3 or 4 moist, 4 to 6 dry, and chroma of 3 to 6 moist and dry. Texture is silty clay, paragravelly silty clay, clay, and paragravelly clay with 40 to 60 percent clay. It has 0 to 10 percent gravel, 0 to 25 percent paragravel, and 0 to 5 percent paracobbles.
The BCt horizon has hue of 2.5Y, 10YR or 7.5YR, value of 4 or 5 moist, 4 to 6 dry, and chroma of 4 to 6 moist and dry. Texture of the fine-earth fraction is silty clay or clay with 40 to 60 percent clay. It has 0 to 10 percent gravel, 10 to 50 percent paragravel, and 0 to 5 percent paracobbles.
COMPETING SERIES: These are the Apt and Wintley series in the same family, and the Absaquil, Hazelcamp, and Skookumhouse soils in a similar family. Absaquil, Apt, Skookumhouse, and Wintley soils are deeper than 40 inches to bedrock. In addition, Wintley soils have very gravelly 2C horizon at a depth of 40 inches or more. Hazelcamp soils have Bt horizons with hue of 5YR or 2.5YR. Absaquil, Hazelcamp, and Skookumhouse soils are currently in a mixed mineralogy class.
GEOGRAPHIC SETTING: McDuff soils occur on summits, shoulder slopes, and backslopes of mountains. Elevations are 300 to 3,300 feet. Where these soils are mapped in the Oregon Coast Range elevations are typically 300 to 1,800 feet and reach heights of 2,600 feet in the more southern portions of the range in southwest Oregon. Where these soils are mapped in the Oregon Cascade Range the typical elevations are 700 to 2,400 feet, and range up to 3,300 feet in the most southern geographic extent of the Cascades. Slopes are 0 to 75 percent. The soils formed in clayey colluvium and residuum derived from siltstone, sandstone, tuffaceous agglomerate, and metasedimentary rock types. The climate is characterized by warm, wet winters and hot, moist summers. The mean annual precipitation is typically 55 to 90 inches, but ranges to 130 inches in the most southern geographic extent of the soil. The mean annual temperature is 45 to 55 degrees F. The frost-free period is 120 to 240 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Absaquil, Apt and Peavine soils and the Bohannon, Digger, Honeygrove, Klickitat, Orford, Preacher, Slickrock, and Trask soils. All of these soils occur on mountains. Bohannon, Digger, Klickitat, Preacher, Slickrock, and Trask soils have less than 35 percent clay and lack argillic horizons. Honeygrove and Peavine soils have Bt horizons with hue of 2.5YR or 5YR. Absaquil soils are greater than 40 inches deep to bedrock. Apt, Orford, and Honeygrove soils are greater than 60 inches deep to bedrock.
DRAINAGE AND PERMEABILITY: Well drained; moderately slow permeability.
USE AND VEGETATION: The McDuff soils are used for timber production, recreation, wildlife habitat, and watersheds, with minor acreage used in Christmas tree production. The potential native vegetation is Douglas-fir, bigleaf maple, red alder, creambush oceanspray, salal, western hazel, vine maple, cascade Oregongrape, western swordfern, western brackenfern, baldhip rose, Pacific dogwood, violet, and trailing blackberry. A minor amount of western hemlock and western redcedar may also be present in some areas.
DISTRIBUTION AND EXTENT: Coast Range and western foot slopes of the Cascade Range; MLRA 1, 3. The series is of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Polk County, Oregon, 1977.
REMARKS: Diagnostic horizons and features of this pedon include:
Umbric epipedon - from 1 to 27 inches (A1, A2, BA, and Bt1 horizons)
Argillic horizon - from 20 to 39 inches (Bt1, Bt2, and BCt horizons)
Particle-size control section - from 20 to 39 inches
Paralithic contact - 39 inches (Cr)
Depths to diagnostic horizons and features are measured from the top of the first mineral horizon.
Classification revised 01/2000 to Fine, isotic, mesic Typic Haplohumults based on changes in the Keys To Soil Taxonomy, 8th edition.