LOCATION GRASSYKNOB OR
Established Series
Rev. MHF/RWL
06/2011
GRASSYKNOB SERIES
The Grassyknob series consists of moderately deep, well drained soils formed in colluvium and residuum derived dominantly from metasedimentary or metavolcanic rock types. Grassyknob soils occur in open grassland areas on broad ridgetops, stable benches, and south-facing side slopes of coastal hills and mountains. Slopes are 0 to 60 percent. The mean annual precipitation is about 85 inches and the mean annual temperature is about 51 degrees F.
TAXONOMIC CLASS: Fine-loamy, isotic, isomesic Andic Humudepts
TYPICAL PEDON: Grassyknob medial silt loam - grassland, on a 22 percent southwest-facing slope at an elevation of 540 feet. (When described on October 10, 1991 the soil was dry to a depth of 12 inches and moist below this depth. Colors are for moist soil unless otherwise noted.)
A--0 to 6 inches; very dark gray (10YR 3/1) medial silt loam, dark gray (10YR 4/1) dry; moderate very fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine and fine, and few medium roots; many very fine tubular pores; 10 percent paragravel; strongly acid (pH 5.2); clear smooth boundary. (5 to 14 inches thick)
AB--6 to 12 inches; very dark gray (10YR 3/1) medial silt loam dark gray (10YR 4/1) dry; moderate very fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine and fine, and few medium roots; many fine and very fine tubular pores; 5 percent gravel and 10 percent paragravel; strongly acid (pH 5.2); gradual smooth boundary. (0 to 10 inches thick)
Bw1--12 to 19 inches; very dark grayish brown (10YR 3/2) silty clay loam, dark grayish brown (10YR 4/2) dry: moderate fine subangular blocky structure; hard, firm, slightly sticky and slightly plastic; common very fine and fine, and few medium roots; many fine and very fine tubular pores; 10 percent gravel and 5 percent paragravel; strongly acid (pH 5.4); gradual smooth boundary.
Bw2--19 to 28 inches; dark grayish brown (10YR 4/2) silty clay loam, brown (10YR 4/3) dry; moderate fine and medium subangular blocky structure; hard, friable, sticky and plastic; common very fine and fine, and few medium roots; common fine tubular pores; 10 percent gravel and 10 paragravel; strongly acid (pH 5.4); clear smooth boundary.
Bw3--28 to 36 inches; brown (10YR 4/3) cobbly clay loam, brown (10YR 5/3) dry; moderate medium subangular blocky structure; hard, firm, sticky and plastic; few fine and medium roots; common fine tubular pores; 10 percent cobbles, 10 percent gravel and 15 percent soft rock fragments; strongly acid (pH 5.4); abrupt wavy boundary. (Combined thickness of the Bw horizon is 10 to 24 inches)
R---36 inches; fractured sandstone.
TYPE LOCATION: Curry County, Oregon; located about 1,650 feet south and 1,400 feet east of the northwest corner of section 18, T. 36 S., R. 14 W. (Latitude 42 degrees, 27 minutes, 48 seconds N.; Longitude 124 degrees, 24 minutes, 35 seconds W.)
RANGE IN CHARACTERISTICS: The mean annual soil temperature is 51 to 54 degrees F. The difference between mean summer and mean winter soil temperature varies from 5 to 9 degrees F. The soils are usually moist but are dry for less than 45 consecutive days in all parts between depths of 4 and 12 inches in the four months following the summer solstice. The particle-size control section has 27 to 35 percent clay and 0 to 30 percent total rock fragments. Depth to bedrock and solum thickness is 20 to 40 inches. The umbric epipedon is 10 to 20 inches thick and may include the upper part of the Bw horizon. The upper 7 to 14 inches has a bulk density of 0.85 to 1.0 g/cm3 and acid oxalate extractable aluminum plus one-half iron of 1.0 to 3.0 percent. Soil reaction is strongly acid to very strongly acid throughout.
The A horizon has hue of 10YR or 7.5YR, value of 2 or 3 moist, 3 t0 5 dry and chroma of 1 or 2 moist and dry. It is medial silt loam and has 0 to 10 percent gravel and 0 to 10 percent paragravel. Organic matter is 8 to 12 percent.
The AB horizon has hue of 10YR or 7.5YR, value of 2 or 3 moist, 3 to 5 dry and chroma of 1 to 3 moist and dry. It has 20 to 25 percent clay and 0 to 10 percent gravel with 0 to 10 percent paragravel.
The Bw horizon has hue of 10YR or 2.5Y, value of 3 to 5 moist, 4 to 6 dry and chroma of 2 or 3 moist and dry. It is silty clay loam, clay loam, or cobbly clay loam with 27 to 35 percent clay. It has 5 to 10 percent gravel, 0 to 20 percent cobbles, and 0 to 30 percent paragravel.
COMPETING SERIES: These are the
Horseprairie,
Reedsport,
Skipanon, and
Svensen series. Horseprairie soils are more than 60 inches deep to bedrock. Reedsport soils are 20 to 40 inches deep to a paralithic contact. Skipanon and Svensen soils are 40 to 60 inches deep to bedrock.
GEOGRAPHIC SETTING: Grassyknob soils occur in open grassland areas on broad ridgetops, stable benches, and south-facing side slopes of coastal hills and mountains. Slopes are 0 to 60 percent. The soils formed in colluvium and residuum derived dominantly from metasedimentary or metavolcanic rock types of the Dothan Formation. Elevations are 200 to 1,300 feet. The climate is humid, characterized by cool, wet winters and cool, moist summers with fog. A strong marine influence limits the diurnal and annual range of temperature. The mean annual precipitation is 75 to 95 inches. The mean annual temperature is 50 to 53 degrees F. The frost-free period is 200 to 270 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the
Hooskanaden,
Loneranch,
Millicoma,
Reinhart,
Sebastian, and
Whaleshead, and competing
Reedsport and
Svensen soils. All of these soils occur on broad ridgetops or side slopes of coastal hills and mountains. Hooskanaden, Loneranch, Reinhart, and Sebastian soils occur in open grassland areas. All the other soils are forested. Hooskanaden soils are very deep to bedrock, clayey, and somewhat poorly drained. Loneranch soils are moderately well drained and have mottles with chroma of 2 or less below 20 inches. Millicoma soils are loamy-skeletal and 20 to 40 inches deep to a paralithic contact. Reinhart soils are 10 to 20 inches deep to a lithic contact. Sebastian soils are loamy-skeletal, 10 to 20 inches deep to bedrock, and have serpentinitic mineralogy. Whaleshead soils are very deep and loamy-skeletal.
DRAINAGE AND PERMEABILITY: Well drained; moderately slow permeability.
USE AND VEGETATION: Grassyknob soils are used for pasture, watershed, and wildlife habitat. Native vegetation is dominated by grasses, with scattered amounts of Sitka spruce, Douglas-fir, western swordfern, western brackenfern, western azalea, and Douglas iris also occurring.
DISTRIBUTION AND EXTENT: Coastal hills and mountains of southwestern Oregon; MLRA 4A. The series is not extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Curry County, Oregon, 1995.
REMARKS: Diagnostic horizons and features recognized in this pedon include:
Umbric epipedon - from the surface to a depth of 19 inches (A, AB, Bw1 horizons).
Cambic horizon - from a depth of 19 to 36 inches (Bw2, Bw3 horizons).
Andic feature - from a depth of 0 to 12 inches (A and AB horizons).
The zone from 0 to 36 inches has 9 to 26 percent base saturation by ammonium acetate and has 20 to 60 kilograms of organic carbon per square meter to a depth of 36 inches (based on lab data).
Particle-size control section - the zone from 10 to 36 inches (part of the AB, Bw1, Bw2, and Bw3 horizons).
ADDITIONAL DATA: Reference sample from pedon 91P 329, samples 91P1965-1968 from Curry County, Oregon samples by NSSL at Lincoln, NE, 4/92.
National Cooperative Soil Survey
U.S.A.