LOCATION TREHARNE OREstablished Series
TAXONOMIC CLASS: Fine-silty, isotic, mesic Aquultic Hapludalfs
TYPICAL PEDON: Treharne silt loam, pasture. (Colors are for moist soil unless otherwise noted.)
Ap--0 to 7 inches; very dark grayish brown (10YR 3/2) silt loam, brown (10YR 5/3) dry; massive; slightly hard, friable, slightly sticky and slightly plastic; many fine and very fine and common medium roots; many very fine irregular pores; slightly acid (pH 6.2); abrupt smooth boundary. (6 to 10 inches thick)
A--7 to 15 inches; dark brown (10YR 3/3) silt loam, brown (10YR 5/3) dry; weak, very fine subangular blocky structure; hard, firm, slightly sticky and slightly plastic; common fine and very fine and few medium roots; many very fine irregular pores; very strongly acid (pH 5.0); gradual smooth boundary. (4 to 10 inches thick)
AB--15 to 29 inches; brown (10YR 4/3) silty clay loam, brown (10YR 5/3) dry; moderate fine subangular blocky structure; hard, firm, slightly sticky and moderately plastic; common fine and very fine and few medium roots; many very fine and few medium tubular pores; very strongly acid (pH 5.0); clear wavy boundary. (0 to 14 inches thick)
Bt--29 to 41 inches; brown (10YR 4/3) silty clay loam, light yellowish brown (10YR 6/4) dry; moderate fine subangular blocky structure; hard, firm, moderately sticky and moderately plastic; fine and medium roots; many fine and very fine and few medium tubular pores; common faint clay films on surface of peds; many medium distinct dark grayish brown (10YR 4/2) redox depletions and yellowish brown (10YR 5/6) redox concentrations; very strongly acid (pH 4.8); clear smooth boundary. (8 to 20 inches thick)
C1--41 to 55 inches; dark grayish brown (2.5Y 4/2) silty clay loam, light brownish gray (10YR 6/2) dry; massive; hard, firm, slightly sticky and moderately plastic; few very fine and fine roots; many very fine and fine and few medium tubular pores; common medium prominent yellowish brown (10YR 5/6) redox concentrations; very strongly acid (pH 5.0); clear smooth boundary. (10 to 20 inches thick)
C2--55 to 61 inches; dark gray (5Y 4/1) silty clay, gray (10YR 6/1) dry; massive; hard, firm, moderately sticky and moderately plastic; few very fine and fine roots; few very fine and fine tubular pores; common medium prominent yellowish brown (10YR 5/6) redox concentrations; very strongly acid (pH 5.0).
TYPE LOCATION: Columbia County, Oregon; 300 hundred yards east of Highway 47 next to gravel road in the SE1/4 SE1/4 NW1/4 section 34, T. 5 N,.R. 4 W.; Vernonia, OR 7.5 minute USGS Quad; NAD 1927.
RANGE IN CHARACTERISTICS: The soil is usually moist but is dry for a short period of less than 45 consecutive days between depths of 4 to 12 inches in the four month period following the summer solstice in most years. The mean annual soil temperature is 48 to 55 degrees F. The umbric epipedon is 10 to 20 inches thick. Hue is 10YR, 2.5Y, or 5Y. The particle-size control section has 18 to 35 percent clay content and less than 15 percent coarser than very fine sand. Aquic conditions occur below depth of 20 inches in normal years as indicated by the presence of redox depletions and concentrations. Depth to bedrock is greater than 60 inches.
The A horizon has value of 2 or 3 moist, 4 or 5 dry and chroma of 2 or 3 moist and dry. Texture is silt loam with 15 to 25 percent clay. Reaction is very strongly acid to slightly acid.
The Bt horizon has value of 4 or 5 moist, 5 to 7 dry and chroma of 2 to 6 moist and dry. Texture is silt loam or silty clay loam with 18 to 35 percent clay and less than 15 percent coarser than very fine sand. Redox concentrations occur below 15 inches in some pedons. Redox depletions with chroma of 2 or less are below depths of 24 inches and occur within the top 10 inches of the argillic horizon. It is very strongly acid or strongly acid.
The C horizon has value of 4 or 5 moist, 5 to 7 dry and chroma of 1 to 4 moist. Redox concentrations are distinct or prominent grayish brown, yellowish brown, brown and strong brown. Texture is silt loam, silty clay loam, or silty clay with 18 to 45 percent clay. Reaction is extremely acid to strongly acid.
COMPETING SERIES: There are no competing series. Similar soils include the Eilertsen and McNulty series. Eilertsen soils are well drained. McNulty soils are coarse-loamy and have an ochric epipedon.
GEOGRAPHIC SETTING: Treharne soils occur on low stream terraces along major drainages in the Coast Range Mountains. Elevations are 20 to 1200 feet. Slopes are 0 to 3 percent. These soils formed in mixed silty alluvium derived from volcanic and sedimentary rock types. The climate is characterized by warm wet winters and hot moist summers. The mean annual temperature is 47 to 53 degrees F. The mean annual precipitation is 60 to 100 inches. The frost-free period is 110 to 220 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Natal, Zyzzug, and the competing Eilertsen and McNulty soils. All of these soils occur on stream terraces. Natal soils are poorly drained soils and are fine textured. Zyzzug soils are poorly drained and lack an argillic horizon.
DRAINAGE AND PERMEABILITY: Moderately well drained; moderately slow permeability. A seasonal water table is at its uppermost limit from November to April.
USE AND VEGETATION: These soils are used for hay, pasture, timber production, recreation, homesite
development and wildlife habitat. Native vegetation is Douglas fir, western hemlock, western redcedar, red alder, red huckleberry, cascade Oregongrape, western swordfern, common snowberry, Pacific serviceberry and bitter cherry.
DISTRIBUTION AND EXTENT: Along river valley low stream terraces of the Coast Range Mountains in western Oregon; MLRA 1. The series is inextensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Columbia County, Oregon, 1983. The source of the name is taken from the community of Treharne in Columbia County.
REMARKS: Diagnostic horizons and features in this pedon include:
Umbric epipedon - from surface to 15 inches (Ap and A horizons)
Argillic horizon - from 29 to 41 inches (Bt horizon)
Aquultic feature - redox depletions with chroma of 2 from depths of 29 to 41 inches (Bt horizon)
Particle-size control section from 29 to 41 inches
Series Revision Date - 08/2002 from mixed mineralogy to isotic mineralogy.