LOCATION YAMHILL                 OR

Inactive Series
Rev. GEO/AON
03/2016

YAMHILL SERIES

The Yamhill series is a member of the fine, mixed, mesic family of Pachic Ultic Haploxerolls. Typically, Yamhill soils have dark brown A horizons and dark reddish brown, silty clay B2 horizons underlain by basalt bedrock at depth of 39 inches. The sola are medium acid.

TAXONOMIC CLASS: Fine, mixed, superactive, mesic Pachic Ultic Haploxerolls

TYPICAL PEDON: Yamhill silt loam, pasture. (Colors are for moist soil unless otherwise noted.)

Ap--0 to 7 inches; dark brown (7.5YR 3/2) silt loam, brown (7.5YR 5/4) dry; moderate fine and very fine subangular blocky structure; hard, friable, slightly sticky, slightly plastic; many fine roots; many fine pores; slightly acid (pH 6.2); abrupt smooth boundary. (6 to 8 inches thick)

B1--7 to 16 inches; dark brown (7.5YR 3/2) silty clay loam, brown (7.5YR 5/4) dry; moderate fine subangular blocky structure; hard, friable, sticky, plastic; common fine roots; many very fine pores; medium acid (pH 6.0); clear smooth boundary. (8 to 11 inches thick)

B21--16 to 24 inches; dark reddish brown (5YR 3/3) silty clay, reddish brown (5YR 5/4) dry; strong medium and fine subangular blocky structure; very hard, firm, very sticky, plastic; few fine roots; common very fine pores; medium acid (pH 5.8); clear smooth boundary. (7 to 10 inches thick)

B22--24 to 36 inches; dark reddish brown (5YR 3/3) silty clay, reddish brown (5YR 5/4) dry; moderate medium subangular blocky structure; very hard, firm, very sticky, very plastic; common very fine pores; few fine basalt fragments, medium acid (pH 6.0); clear smooth boundary. (11 to 14 inches thick)

IIB23tb--36 to 39 inches; dark reddish brown (5YR 3/4) clay, reddish brown (5YR 5/4) dry; weak medium subangular blocky structure; very hard, very firm, very sticky, very plastic; common fine pores; common thin clay films with a few moderately thick films on peds and in pores and channels; 30 percent fine weathered basalt fragments; medium acid (pH 6.0); abrupt wavy boundary. (0 to 3 inches thick)

IIR--39 to 45 inches; very hard partially weathered fractured basalt bedrock with dark red colored soil coatings and clay films on fracture faces.

TYPE LOCATION: Yamhill County, Oregon; on northwest slope 257 feet east of road about 600 feet north of road curve, SW1/4 NW1/4 NW1/4 section 16, T. 5 S., T. 5 W., W.M.

RANGE IN CHARACTERISTICS: The soils are usually moist but are dry between depths of 4 to 12 inches for 60 to 80 consecutive days during the 4-month period following summer solstice. The mean annual soil temperature ranges from about 54 to 56 degrees F. Thickness of the solum and depth to bedrock range from 20 to 40 inches with 36 to 40 inches the most common.

The A horizon has hue of 7.5YR or 10YR, value of 2 or 3 moist, 4 or 5 dry and chroma of 2 or 3 moist and 3 or 4 dry. Some pedons have a few fine concretions. The A horizon is commonly silt loam, but ranges to silty clay loam.

The B horizon has value of 4 or 5 dry and chroma of 2 through 4 moist and dry. It has strong to moderate structure in the upper part of the B horizon and generally moderate in the lower part. This horizon is silty clay, clay or heavy silty clay loam and has 35 to 50 percent clay. Up to 5 percent fragments are embedded in the lower part of the B horizon in some pedons.

The IIB23tb horizon ranges up to about 3 inches thick and is not present in the thinner sola. It has color characteristics similar to the B2 horizon, but has weak structure, nearly continuous thin or few moderately thick clay films on peds, heavy silty clay or clay texture and 10 to 50 percent fine basalt rock fragments.

COMPETING SERIES: These are the Carlton, Palouse, Price and Steiwer series. Carlton and Palouse soils are fine-loamy, deeper than 40 inches to bedrock and have yellower than 5YR. Steiwer soils have epipedons less than 20 inches thick, are fine-loamy in the control section and have hue yellower than 5YR. Price soils have ochric epipedons and have a base saturation (by NH4OAC) less than 60 percent throughout the upper 30 inches.

GEOGRAPHIC SETTING: The Yamhill soils are on gently sloping to steep smooth, convex uplands at elevations of 260 to 600 feet. The soils formed in fine textured colluvium weathered from basalt flows and breccias that are probably a part of the Tillamook Volcanics and Siletz Volcanics that formed in the early Eocene epoch. The climate is subhumid with cool, moist winter, and warm, dry summers. The annual precipitation is 40 to 50 inches. The average July temperature is 66 degrees F., average January temperature is 38 degrees F., and average annual temperature is 52 to 54 degrees F. The frost-free period is 165 to 210 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Jory, Nekia and Witzel soils. Nekia and Jory soils have fine textured Bt horizons. The Witzel soils are less than 20 inches deep to bedrock.

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

USE AND VEGETATION: Most of the soils have been cleared and are used for orchards, small grain, hay and pasture. Native vegetation is mainly Oregon white oak, rosebush, poison-oak, annual and perennial grasses and widely spaced Douglas-fir.

DISTRIBUTION AND EXTENT: Along the northwestern part of the Willamette Valley in northwestern Oregon. The series is inextensive.

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

SERIES ESTABLISHED: Yamhill County, Oregon, 1974.

REMARKS: The Yamhill soils were formerly classified as Reddish Brown Lateritic soils.

NATIONAL COOPERATIVE SOIL SURVEY
U.S.A.