LOCATION MACDUNN OR
Established Series
Rev. MHF/DRJ/RWL
06/2011
MACDUNN SERIES
The MacDunn series consists of deep, well drained soils formed in clayey colluvium derived from basalt. MacDunn soils occur on side slopes of foothills and mountains. Slopes are 30 to 90 percent. The mean annual precipitation is about 60 inches and the mean annual temperature is about 52 degrees F.
TAXONOMIC CLASS: Clayey-skeletal, mixed, superactive, mesic Humic Haploxerepts
TYPICAL PEDON: MacDunn gravelly silty clay loam, woodland, on a 40 percent southwest-facing slope at an elevation of 1080 feet. (When described on April 21, 1998 the soil profile was moist throughout. Colors are for moist soil unless otherwise noted.)
Oi--0 to 1 inch; slightly decomposed needles, leaves, twigs, and woody materials.
A--1 to 7 inches; dark brown (7.5YR 3/4) gravelly silty clay loam, brown (7.5YR 4/4) dry; moderate very fine and fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine, common fine, and few medium and coarse roots; many very fine tubular pores; 15 percent gravel and 5 percent cobbles; moderately acid (pH 5.8); clear smooth boundary. (Combined thickness of the A horizon ranges from 5 to 8 inches)
AB--7 to 15 inches; dark brown (7.5YR 3/4) gravelly silty clay loam, brown (7.5YR 4/4) dry; moderate fine and medium subangular blocky structure; hard, firm, moderately sticky and moderately plastic; common fine and medium, and few very fine and coarse roots; many very fine tubular pores; 15 percent gravel and 5 percent cobbles; moderately acid (pH 5.6); clear smooth boundary. (0 to 12 inches thick)
Bw1--15 to 24 inches; dark brown (7.5YR 3/4) very cobbly silty clay, brown (7.5YR 4/4) dry; moderate fine and medium subangular blocky structure; hard, firm, moderately sticky and moderately plastic; common fine and medium, and few very fine and coarse roots; common very fine tubular pores; 30 percent cobbles and 20 percent gravel; strongly acid (pH 5.4); gradual wavy boundary.
Bw2--24 to 38 inches; dark brown (7.5YR 3/4) very cobbly silty clay, brown (7.5YR 4/4) dry; moderate fine and medium subangular blocky structure; hard, firm, moderately sticky and moderately plastic; common fine and medium, and few coarse roots; few very fine tubular pores; 35 percent cobbles and 20 percent gravel; strongly acid (pH 5.2); gradual wavy boundary.
Bw3--38 to 51 inches; dark brown (7.5YR 3/4) extremely cobbly silty clay, brown (7.5YR 4/4) dry; moderate fine subangular blocky structure; hard, firm, moderately sticky and moderately plastic; few fine, medium, and coarse roots; few very fine tubular pores; 45 percent cobbles, 5 percent stones, and 25 percent gravel; strongly acid (pH 5.2); abrupt wavy boundary. (Combined thickness of the Bw horizon ranges from 30 to 40 inches)
2Cr--51 inches; weathered, highly fractured basalt bedrock
TYPE LOCATION: Benton County, Oregon; 1.5 miles southwest of Adair Village, in Oregon State University's McDonald Forest; located about 2100 feet north and 250 feet west of the southeast corner of section 35, T. 10 S., R. 5 W., Willamette Meridian (Latitude 44 degrees, 39 minutes, 25 seconds N; Longitude 123 degrees, 15 minutes, 15 seconds W. NAD27); Airlie South, Oregon USGS 7.5 minutes topographic quadrangle.
RANGE IN CHARACTERISTICS: The mean annual soil temperature ranges from 51 to 55 degrees F. The soils are usually moist but are dry for 45 to 60 consecutive days between depths of 4 and 12 inches following the summer solstice. Depth to fractured bedrock and solum thickness is 40 to 60 inches. Some pedons have up to 5 percent stones on the soil surface. Reaction is strongly acid or moderately acid.
The A horizon has hue of 5YR to 10YR, value of 2 or 3 moist, 3 or 4 dry and chroma of 2 to 4 moist and 3 or 4 dry. Texture is silty clay loam or clay loam with 27 to 35 percent clay. It has 15 to 25 percent gravel, 5 to 10 percent cobbles and 0 to 3 percent stones.
The Bw horizon has hue of 2.5YR to 7.5YR, value of 3 to 5 moist, 4 to 6 dry and chroma of 4 to 6 moist and dry. Texture is silty clay loam, clay loam, silty clay or clay with 35 to 50 percent clay. It has 30 to 60 percent cobbles, 20 to 30 percent gravel and 0 to 5 percent stones.
COMPETING SERIES: This is the
Ritner series. Ritner soils are 20 to 40 inches deep to a lithic contact.
GEOGRAPHIC SETTING: MacDunn soils occur on summit (interfluve component), backslope (head slope or side slope components) and footslope positions (base slope component) on steep to very steep side slopes of foothills and mountains along the margins of the Willamette Valley in Oregon. The summit position typically has a convex-linear slope shape; the backslope position is typically concave-convex or convex-convex in shape; while the footslope position is typically linear-convex or convex-concave in shape. Slopes are 30 to 90 percent. Elevation is 240 to 2,200 feet. The soils formed in clayey colluvium derived dominantly from the Siletz River Volcanics Formation. The climate is characterized by warm, wet winters and hot, dry summers. The mean annual precipitation is 50 to 70 inches. The mean annual temperature is 48 to 54 degrees F. The frost-free period is 160 to 210 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the
Jory,
Nekia,
Price,
Ritner,
Witzel, and
Yamhill soils. Jory, Nekia and Yamhill soils occur on foothills along the margins of the
Willamette
Valley, Oregon. Price, Ritner and Witzel soils occur on steep to very steep side slopes of foothills and mountains. Jory and Nekia soils have argillic horizons. Yamhill soils have mollic epipedons and are 20 to 40 inches deep to a lithic contact. Price soils are fine textured, have less than 35 percent total rock fragments in the particle-size control section, and are greater than 60 inches deep to bedrock. Ritner soils are fine textured, have more than 35 percent total rock fragments in the particle-size control section and are 20 to 40 inches deep to a lithic contact. Witzel soils are shallower than 20 inches to a lithic contact and have more than 35 percent total rock fragments in the particle-size control section.
DRAINAGE AND PERMEABILITY: Well drained; moderately slow permeability.
USE AND VEGETATION: These soils are used for timber production, hay and pasture, limited homesite development, wildlife habitat and watersheds. The native vegetation is Douglas fir, grand fir, bigleaf maple, Oregon white oak, western brackenfern, western swordfern, common snowberry, western hazel, creambush oceanspray, poison oak and wild rose.
DISTRIBUTION AND EXTENT: Foothills and mountains along the margins of the Willamette Valley, Oregon; MLRA 2. The series is of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Benton County, Oregon, 2004.
REMARKS: Diagnostic horizons and features recognized in this pedon include:
Ochric epipedon - from 1 to 15 inches (A, AB horizons).
Humic subgroup - meets color requirements to a depth of 51 inches.
Cambic horizon - from a depth of 15 to 51 inches (Bw1, Bw2, Bw3 horizons)
Particle-size control section - from depths of 11 to 41 inches (part of the AB, all of the Bw1 and Bw2, and part of the Bw3 horizons)
This soil was not previously recognized in the Benton County Area Soil Survey report. Field observations and documentation from several counties in the Willamette Valley update area, indicate the MacDunn soils occur consistently and extensively enough to be recognized and mapped as a named soil series. MacDunn soils occur on the Looney geomorphic surface. Depths to diagnostic horizons and features in the range of characteristics start from the mineral soil surface. Lab data from the MacDunn type location and on similar soils indicate a superactive CEC activity class and more than 60 percent base saturation. This resulted in a change in classification to clayey-skeletal, mixed, superactive, mesic Humic Haploxerepts
ADDITIONAL DATA: Characterization data available for sample # S00OR-003-005, NSSL, Lincoln, NE.
National Cooperative Soil Survey
U.S.A.