LOCATION SILCOX OR
Established Series
Rev. AON/RWL
06/2011
SILCOX SERIES
The Silcox series consists of very deep, well drained soils that formed in moderately coarse textured glacial till weathered mostly from andesitic and basaltic rocks. Silcox soils are on hillsides in glaciated valleys in mountainous areas and have slopes of 5 to 80 percent. The mean annual precipitation is about 100 inches and the mean annual temperature is about 48 degrees F.
TAXONOMIC CLASS: Coarse-loamy, isotic, mesic Andic Humudepts
TYPICAL PEDON: Silcox gravelly fine sandy loam, forested. (Colors are for moist soil unless otherwise noted.)
Oi--0 to 1 inch; slightly decomposed litter of needles, leaves, twigs, cones, etc.
A1--1 to 2 inches; very dark gray (10YR 3/1) gravelly fine sandy loam, very dark grayish brown (10YR 3/2) dry; massive; many roots; few clean silica sand grains; moderately acid (pH 5.9); abrupt smooth boundary. (0 to 1 inch thick)
A2--2 to 11 inches; dark brown (7.5YR 3/2) gravelly fine sandy loam, brown (7.5YR 4/3) dry; weak very fine and fine subangular blocky structure; soft, very friable, nonsticky and slightly plastic; weakly smeary; many roots; many very fine and fine irregular pores; few shot; 20 percent gravel and cobbles; moderately acid (pH 5.8); gradual wavy boundary. (5 to 15 inches thick)
Bw--11 to 24 inches; dark brown (10YR 3/3) cobbly fine sandy loam, variegated with very dark brown (10YR 2/2) and dark yellowish brown (10YR 4/4), brown (10YR 4/3) dry; weak very fine and fine subangular blocky structure; soft, very friable, nonsticky and slightly plastic; many roots; many very fine and fine irregular pores; few shot; few small pumice fragments; 20 percent cobbles and gravel; moderately acid (pH 5.8); gradual wavy boundary. (8 to 18 inches thick)
C--24 to 61 inches; dark yellowish brown (10YR 4/4) very cobbly fine sandy loam, brown (10YR 5/3) dry; massive; soft, very friable, nonsticky and slightly plastic; common roots; many very fine and fine irregular pores; few soft dark yellowish brown concretions, 5 to 10 mm in diameter; few small pumice fragments; 40 percent cobbles and gravel; moderately acid (pH 6.0).
TYPE LOCATION: Clackamas County, Oregon; 100 feet south of Dibble Road; SE1/4 SE1/4 section 19, T.2S., R.8E., W.M.
RANGE IN CHARACTERISTICS: The soil is usually moist but is dry between depths of 8 to 24 inches for a short period of less than 45 consecutive days after the summer solstice. The mean annual soil temperature is 47 to 52 degrees F. Thickness of the solum is 18 to 30 inches. Depth to a cemented basal till layer ranges from 4 to 6 feet. Depth to bedrock commonly is greater than 60 inches. The control section ranges from fine sandy loam to sandy loam and has 10 to 35 percent rock fragments and 10 to 18 percent clay. Moist bulk density is 0.85 to 0.95 grams per cubic centimeter throughout.
The A horizon is dark gray (10YR 3/1), very dark grayish brown (10YR 3/2) or dark brown (7.5YR 3/2) when moist. It has an estimated acid oxalate extractable aluminum plus one-half iron of 1.0 to 2.0 percent and less than 2.0 cmol per kg fine earth of 1N KCL extractable aluminum.
The Bw horizon colors are variegated with the dominant moist value of 3 to depth of 20 inches or more and chroma of 3 to depth of 20 inches or more and 3 or 4 below 20 inches.
The C horizon has value of 5 or 6 dry, and chroma of 3 or 4 moist and dry. Rock fragments range from 25 to 50 percent.
COMPETING SERIES: This is the
Jimbo series. Jimbo soils lack rock fragments and pumice fragments within the particle-size control section.
GEOGRAPHIC SETTING: Silcox soils are on smooth slopes in glaciated valleys in the Cascade Mountains at elevations of 1,000 and 3,000 feet. The slopes range from 5 to 80 percent. The soils formed in moderately coarse textured glacial till of late Pleistocene origin and weathered mostly from andesitic and basaltic rocks. The climate is characterized by warm wet winters and hot moist summers. The mean annual precipitation is 80 to 120 inches. The mean January temperature is 34 degrees F., and the mean July temperature is 64 degrees F. The mean annual temperature is 45 to 50 degrees F. The frost-free period is 100 to 160 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the
Brightwood and
Enola soils and less commonly
Crutch and
Multorpor soils. Brightwood soils are loamy-skeletal and 20 to 40 inches deep to bedrock. Crutch and Multorpor soils are sandy-skeletal and are on associated terraces. Enola soils have ochric epipedons.
DRAINAGE AND PERMEABILITY: Well drained; moderately rapid permeability.
USE AND VEGETATION: The primary use of the Silcox soils are for producing timber and for recreation and wildlife habitat. Overstory vegetation is Douglas-fir, western hemlock, western redcedar and red alder. Understory vegetation dominantly is swordfern, oxalis, and devils club.
DISTRIBUTION AND EXTENT: Cascade Mountains of northwest Oregon; MLRA 3. The series is of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Clackamas County, Oregon (Bull Run, Sandy Area), 1976.
REMARKS: Diagnostic horizons and features recognized in this pedon:
Umbric epipedon - from 1 to 11 inches (A1 and A2 horizons)
Cambic horizon - from 11 to 24 inches (Bw horizon)
Andic feature - from 1 to 11 inches having a moist bulk density of 0.85 to 0.95 grams per cubic centimeter and an estimated acid oxalate extractable aluminum plus one-half iron of 1.0 to 2.0 percent.
Particle-size control section - from 11 to 41 inches (Bw and upper 17 inches of the C horizon) with a weighted average of 31 percent rock fragments.
ADDITIONAL DATA: Characterization data for one pedon (FS63-Ore-045-29 (1-4)) by Oregon State University. (Unpublished)
National Cooperative Soil Survey
U.S.A.