LOCATION TOLKE OREstablished Series
TAXONOMIC CLASS: Medial, ferrihydritic, mesic Alic Hapludands
TYPICAL PEDON: Tolke silt loam - forested, on a 5 to 30 percent southwest-facing slope at 1,840 feet elevation. (Colors are for moist soils unless otherwise noted.)
A--0 to 6 inches; dark brown (7.5YR 3/2) silt loam, brown (7.5YR 5/4) dry; strong, fine, granular structure; slightly hard, friable, slightly sticky and slightly plastic; moderately smeary; many fine roots; many, very fine, irregular pores; 15 percent very fine concretions; strongly acid (pH 5.2); clear, smooth boundary.
AB--6 to 10 inches; dark brown (7.5YR 4/4) heavy silt loam, yellowish red (5YR 5/6) dry; strong, very fine,subangular blocky structure; slightly hard, friable, slightly sticky and moderately plastic; moderately smeary; many fine roots; many, very fine, tubular pores; common fine concretions; strongly acid (pH 5.2); clear, smooth boundary. (Combined thickness of the A horizon is 6 to 10 inches)
Bw1--10 to 17 inches; dark brown (7.5YR 4/4) silty clay loam, reddish-yellow (5YR 6/6) dry; moderate, fine, subangular blocky structure; slightly hard, friable, slightly sticky and moderately plastic; weakly smeary; many fine roots; many, very fine, tubular pores; very strongly acid (pH 4.8); clear, smooth boundary.
Bw2--17 to 26 inches; strong brown (7.5YR 4/6) silty clay loam, reddish-yellow (5YR 6/6) dry; moderate, fine, subangular blocky structure; slightly hard, friable, slightly sticky and moderately plastic; weakly smeary; common fine roots; many, very fine, tubular pores; very strongly acid (pH 4.8); clear, smooth boundary.
Bw3--26 to 45 inches; strong brown (7.5YR 4/6) silty clay loam, reddish-yellow (5YR 6/6) dry; weak, medium, subangular blocky structure; slightly hard, friable, slightly sticky and moderately plastic; weakly smeary; common fine roots; many, very fine, tubular pores; very strongly acid (pH 4.8); clear, smooth boundary.
Bw4--45 to 61 inches; strong brown (7.5YR 4/6) silty clay loam, reddish-yellow (5YR 6/6) dry; weak, coarse, subangular blocky structure; hard, firm, slightly sticky and moderately plastic; weakly smeary; few fine roots; many very fine, tubular pores; common, discontinuous, distinct clay films in pores and on peds; very strongly acid (pH 4.6). (Combined thickness of the Bw horizon is 50 to 65 inches)
TYPE LOCATION: Washington County, Oregon; about 4 miles southeast of the summit of Hwy 6; about 100 feet east of a forest road; about 2,500 feet south and 400 feet east of the northwest corner of section 9 T.1N., R.5W.
RANGE IN CHARACTERISTICS: The soils are usually moist but are dry throughout between depths of 4 and 12 inches for a period of less than 45 consecutive days following the summer solstice. The mean annual soil temperature is 47 to 52 degrees F. The solum is more than 50 inches thick. Depth to bedrock is more than 60 inches. The solum is weakly or moderately smeary and has a moist bulk density of 0.70 to 0.90 g/cubic centimeter.
The A horizon has hue of 7.5YR or 10YR, value of 2 to 4 moist and 4 or 5 dry and chroma of 2 to 4 moist and 3 to 6 dry. This horizon is commonly silt loam but includes loam. Concretions range from about 0 to 15 percent. Soil reaction is very strongly or strongly acid.
The Bw horizon has hue of 7.5YR or 10YR, value of 3 to 6 moist and 5 to 8 dry and chroma of 4 to 6 moist and 6 to 8 dry. It is silty clay loam and averages 27 to 35 percent apparent clay and less than 15 percent coarser than very fine sand. Soil reaction is very strongly or strongly acid.
A few rock fragments from the underlying rock are embedded in the C horizons of some pedons. The underlying rock is usually tuffaceous siltstone, but basalt is found below some pedons.
COMPETING SERIES: This is the Anunde, Belle, Hemcross, Skamo, Wadell, and Zenger soils. Hemcross, Skamo, Wadell, and Zenker soils have umbric epipedons. Anunde soils have an apparent clay content of 18 to 27 percent in the Bw horizon above 40 inches. Belle soils average less than 27 percent clay in the particle-size control section, are formed in alluvium on low terraces and fans, and are subject to rare flooding. Hencross, Skamo, Wadell, and Zenker soils have umbric epipedons. In addition, Skamo soils have redox concentrations at a depth of 24 to 40 inches. Wadell soils have 15 to 30 percent rounded gravel in the particle-size control section, and stratified 2C horizons. Zenker soils have 20 to 27 percent clay and 35 to 80 percent sandstone paragravel in the particle-size control section.
GEOGRAPHIC SETTING: Tolke soils are on mountains in the Coast Range at elevations of 800 to 2,500 feet. Slopes are 0 to 60 percent but are commonly less than 30 percent. The soils formed in mixed colluvium weathered mostly from tuffaceous sedimentary rock. The climate is characterized by warm wet winters and hot moist summers. The mean July temperature is 64 degrees F.; the mean winter temperature is 34 degrees F.; and the mean annual temperature is 45 to 50 degrees F. The mean annual precipitation is 60 to 100 inches. The frost free period is 100 to 200 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Astoria, Hembre, Melby and Olyic soils. Astoria soils have umbric epipedons and have silty clay or clay B horizons. Hembre soils have umbric epipedons, are fine-loamy and are 40 to 60 inches to basalt bedrock. Melby soils are fine textured and 40 to 60 inches to sedimentary bedrock. Olyic soils are fine-loamy, have argillic horizons, and are 40 to 60 inches to basalt bedrock.
DRAINAGE AND PERMEABILITY: Well drained; moderate permeability.
USE AND VEGETATION: The soils are used mainly for timber production. Small cleared area are used for improved pasture and homesites. Native vegetation is mainly Douglas fir, bigleaf maple, red alder, and vine maple with shrubs consisting of cascade Oregongrape, salal and western swordfern.
DISTRIBUTION AND EXTENT: Along low summit ridges and eastern slopes of the Coast Range in northwestern Oregon; MLRA 1. The series is of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Washington County, Oregon, 1975.
REMARKS: This draft reflects a change in pedon location from Tillamook County to Washington County and a change in mineralogy to ferrihydritic.
Diagnostic horizons and features recognized in this pedon include:
Ochric epipedon - from 0 to 10 inches (A and AB horizons)
Cambic horizon - from 10 to 61 inches (Bw1, Bw2, Bw3 and Bw4 horizons)
Andic soil properties - from surface to 61 inches.
Particle-size control section - from surface to 40 inches.