LOCATION MCWHINNEY CATentative Series
TAXONOMIC CLASS: Fine-silty, mixed, superactive, isomesic Typic Haplohumults
TYPICAL PEDON: McWhinney on a southeast facing slope of 20 percent under a logged forest of redwood, Douglas-fir, tanoak, pacific swordfern, and evergreen huckleberry. (Colors are for moist soil unless otherwise stated.) When described on August 14, 2002 the soil was moist throughout.
Oi--0 to 5 centimeters; Slightly decomposed redwood needles, bark, and twigs, moss, and evergreen huckleberry leaves; abrupt wavy boundary. (0 to 5 centimeters thick)
A--5 to 31 centimeters; very dark grayish brown (10YR 3/2) silt loam, grayish brown (10YR 5/2) dry; strong fine subangular blocky structure; moderately hard, friable, slightly sticky and slightly plastic; many fine, common medium and coarse roots; common very fine tubular pores; 1 percent gravel; slightly acid (pH 6.4); clear wavy boundary. (5 to 45 centimeters thick)
ABt--31 to 48 centimeters; brown (10YR 4/3), silty clay loam, brown (10YR 5/3) dry; strong fine subangular blocky structure; moderately hard, friable, slightly sticky and moderately plastic; common fine, medium, and coarse roots; common very fine, fine tubular, and medium tubular pores; common prominent very dark grayish brown (10YR 3/2) organoargillans on all faces of peds; 5 percent gravel; moderately acid (pH 6.0); gradual wavy boundary.
Bt--48 to 110 centimeters; light olive brown (2.5Y 5/3) paragravelly silty clay loam, light yellowish brown (2.5Y 6/3) dry; strong fine and medium subangular blocky structure; moderately hard, friable, slightly sticky and moderately plastic; common fine, medium, coarse, and very coarse roots; common very fine, fine, and medium tubular pores; common distinct dark grayish brown (10YR 4/2) clay films on all faces of peds; 20 percent gravel; strongly acid (pH 5.4); clear irregular boundary. (combined thickness of ABt and Bt horizons is 25 to 120 centimeters)
Cr--110 to 120 centimeters; 60 percent light yellowish brown (2.5Y 6/4) and 30 percent yellowish brown (10YR 5/6) and 10 percent light gray (2.5Y 7/2); few distinct dark brown (7.5YR 3/3) clay films on weakly to moderately cemented siltstone rock fragments, moderate excavation difficulty, fractures 10 to 45 centimeters apart, breaking into angular to subangular blocks.
TYPE LOCATION: Humboldt County, California; Located approximately 1 kilometer north of Grizzly Creek State Park, Pacific Lumber Company Road L83 to L83.20, 1.8 kilometers to skid trail on north side of road; northwest quarter of the southwest quarter of section 1, T. 1N, R. 2E HB&M; 40 degrees 29 minutes 46 seconds north latitude and 123 degrees 54 minutes 17 seconds west longitude, NAD 83; USGS Redcrest 7.5 minute series Quadrangle; UTM 10T 423331e 4483223n.
RANGE IN CHARACTERISTICS:
Soil moisture: The soil moisture control section, between the depths of 11 to 36 centimeters, is not dry in any part for as long as 90 cumulative days in normal years. The soils have a udic moisture regime.
Soil Temperature: The mean annual soil temperature at 50 centimeters is 10 to 13 degrees C. The difference between mean summer and mean winter temperature is less than 6 degrees C.
Base Saturation: By the Ammonium acetate method is less than 35 percent at 125cm below the upper boundary of the argillic horizon.
Organic matter: There is 15 to 25 kg organic carbon per square meter to a depth of one meter.
Particle size control section (weighted average):
ParaRock fragments: 0 to 15 percent paragravel
Clay content: 24 to 35 percent
A horizon Hue: 10YR or 2.5Y
Value: 2 to 4 moist, 4 to 6 dry
Chroma: 1 to 3, moist or dry
Texture of fine earth: silt loam
Para Rock fragments: 0 to 10 percent
Clay content: 12 to 27 percent
Reaction: moderately acid to neutral
Bt horizons
Hue: 10YR or 2.5Y
Value: 3 to 5 moist, 5 to 7 dry
Chroma: 2 to 6, moist or dry
Texture of fine earth: silt loam, silty clay loam, and clay loqm
Para Rock fragments: 0 to 15 percent subangular moderately cemented siltstone paragravel in the upper part, 5 to 65 percent subangular moderately cemented siltstone paragravel in the lower part, and 0 to 15 percent subangular weakly to moderately cemented siltstone paracobble throughout.
Clay content: 24 to 36 percent
Reaction: strongly acid to moderately acid
COMPETING SERIES: There are no other series in this family.
GEOGRAPHIC SETTING: McWhinney soils are on mountain ridges and convex slope positions. Slopes are 15 to 110 percent. Elevations are 60 to 640 meters. These soils formed in residuum from Quaternary and Tertiary age siltstone and fine-grained sandstone on the Undifferentiated Wildcat Group. The climate is humid with cool, foggy summers and cool, rainy winters. Mean annual precipitation is 890 to 2160 millimeters. Mean January temperature is about 9 degrees C, mean July temperature is about 14 degrees C, and the mean annual temperature is 10 to 13 degrees C. Frost free season is about 240 to 300 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Redcrest (T), Rootcreek (T), and Scoutcamp (T) soils. Redcrest, Rootcreek, and Scoutcamp soils have clay contents that do not decrease more than 20 percent from the maximum within 150 centimeters of the mineral soil surface. Redcrest soils are on backslopes with thicker colluvium and on shoulders. Rootcreek soils are on concave positions and in drainageways. Scoupcamp soils are on mountain slopes.
DRAINAGE AND PERMEABILITY: Well drained, medium to high runoff, moderate permeability.
USE AND VEGETATION: This soil is used for commercial timber production, wildlife habitat, and watershed. Natural vegetation includes coast redwood, Douglas fir, tan oak, evergreen huckleberry, salal, swordfern, thimbleberry, and red huckleberry.
DISTRIBUTION AND EXTENT: California Coastal Redwood Belt; MLRA 4. The series is not extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES PROPOSED: Humboldt County, California. The name is from a tributary creek to the North Fork of the Elk River, southeast of the town of Eureka.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
1. Mollic epipedon - the zone from 5 to 31 centimeters (A horizon).
2. Argillic horizon - the zone from 31 to 110 centimeters (ABt and Bt horizons).
3. Particle-size control section - the zone from 31 to 81 centimeters (ABt and Bt horizons).