LOCATION THREECHOP CAEstablished Series
TAXONOMIC CLASS: Fine, mixed, semiactive, isomesic Ustic Haplohumults
TYPICAL PEDON: Threechop loam - on a northeast facing convex slope of 15 percent under Douglas-fir and tanoak at 1280 feet elevation. (Colors are for dry soil unless otherwise stated. When described on November 6, 1980 the soil was moist below 10 inches).
Oi--1 inch to 0; tanoak litter.
A--0 to 8 inches; very pale brown (10YR 7/3) loam, yellowish brown (10YR 5/4) moist; weak fine and medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine and fine and few medium roots; common very fine tubular and interstitial pores; 5 percent soft pebbles (2-15mm); strongly acid (pH 5.2); clear wavy boundary. (7 to 10 inches thick)
Bt1--8 to 12 inches; variegated very pale brown (10YR 7/4) and reddish yellow (7.5YR 6/6) clay loam, strong brown (7.5YR 4/6) moist; moderate medium subangular blocky structure; hard, friable, sticky and slightly plastic; common very fine and fine and few medium roots; common very fine interstitial and few very fine and fine tubular pores; few thin clay films on faces of peds and lining pores; 5 percent soft pebbles (2-15mm); strongly acid (pH 5.2); gradual wavy boundary. (3 to 7 inches thick)
Bt2--12 to 17 inches; variegated reddish yellow (7.5YR 6/6) and yellowish red (5YR 5/6) clay, yellowish red (5YR 5/6) and reddish brown (5YR 4/4) moist; weak medium and coarse subangular blocky structure parting to weak medium angular blocky; hard, firm, sticky and plastic; few fine, medium and coarse roots; few fine tubular and common very fine interstitial pores; common thin and moderately thick clay films on faces of peds and lining pores; 5 percent soft pebbles (2-15mm); very strongly acid (pH 5.0); gradual wavy boundary. (5 to 8 inches thick)
Bt3--17 to 26 inches; variegated pink (7.5YR 7/4) and yellowish red (5YR 5/6) clay, yellowish red (5YR 4/6) reddish brown (5YR 4/3) moist; moderate medium and coarse subangular blocky structure parting to moderate medium and coarse angular blocky; very hard, firm, sticky and plastic; few fine, medium and coarse roots; few very fine tubular and interstitial pores; many moderately thick clay films on faces of peds and lining pores; 5 percent soft pebbles (2-15mm); very strongly acid (pH 4.9); gradual wavy boundary. (8 to 12 inches thick)
Bt4--26 to 32 inches; variegated reddish yellow (7.5YR 6/8, 5YR 6/6) clay, yellowish red (5YR 5/6) and reddish brown (5YR 4/4) moist; moderate medium and coarse subangular blocky structure; very hard, firm, sticky and plastic; few fine, medium and coarse roots; common very fine tubular and few very fine interstitial pores; many moderately thick clay films on faces of peds and lining pores; 5 percent soft pebbles (2-15mm); very strongly acid (pH 5.0); gradual wavy boundary. (6 to 10 inches thick)
Bt5--32 to 42 inches; variegated yellowish red (5YR 5/8) and very pale brown (10YR 8/3) clay, yellowish red (5YR 5/6), reddish brown (5YR 4/4) and yellow (10YR 8/6) moist; weak medium subangular blocky structure; hard, firm, slightly sticky and slightly plastic; few medium and coarse roots; few very fine tubular and interstitial pores; many moderately thick and few thick clay films on faces of peds and lining pores; 5 percent soft pebbles (2-15mm); strongly acid (pH 5.1); gradual wavy boundary. (10 to 14 inches thick)
Cr--42 to 57 inches; variegated white (10YR 8/2) and yellowish red (5YR 5/6) fractured soft mudstone and sandstone; fractures are less than 1 millimeter wide and 1 to 4 centimeters apart; few coarse roots along fractures; many moderately thick and few thick clay films on fracture faces. Rock slakes in water.(see remarks)
TYPE LOCATION: Mendocino County, California; Jackson State Forest; 100 feet down a skid trail that intersects Road 240 at a point about 1.8 miles north of its intersection with Road 200; 1500 feet north and 1700 feet west of the southeast corner of sec. 29, T18N., R.15W., Comptche northeast quadrangle.
RANGE IN CHARACTERISTICS: Thickness of the solum and depth to a paralithic contact is 40 to 60 inches. The mean annual soil temperature varies from 52 to 56 degrees F. The difference between mean summer and mean winter temperature is 3 to 8 degrees F. The soil between the depths of 7 and 20 inches is moist in all parts from November 1 to June 1. It is dry in some or all parts from July 1 to October 1 in most years. Clay content averages between 35 and 50 percent in the particle-size control section. Gravel content is 2 to 10 percent throughout the profile. Pebbles are soft to firm when moist.
The A horizon is 10YR 6/3, 7/3, 7/4 or 7.5YR 4/4, 5/4, 7/3. Moist color is 10YR 4/3, 5/4, 5/6 or 7.5YR 4/4,4/6. Clay content ranges from 18 to 27 percent. Organic carbon content ranges from 2 to 5 percent. The base saturation (sum) ranges from 40 to 60 percent. Reaction is strongly or moderately acid.
The Bt horizon is variegated 10YR 7/4, 8/3, 8/4; 7.5YR 5/6, 5/8, 6/6, 6/8, 7/3, 7/4, 7/6; 5YR 4/3, 4/4, 4/6, 5/6, 5/8 or 6/6. Moist color is 10YR 5/6, 8/6; 7.5YR 4/4, 4/6, 5/4, 5/6; 5YR 4/3, 4/4, 4/6, 5/6 or 5/8. It is clay loam or clay. Clay content ranges from 27 to 60 percent. Organic carbon content ranges from 0.9 to 3 percent in the upper 15 inches of the Bt horizon. Base saturation (sum) is 10 to 50 percent and decreases to less than 35 percent in the lower part of the horizon. Reaction is very strongly through moderately acid.
The Cr horizon becomes harder and coarser in texture with increasing depth. Some pedons have a C horizon.
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING: The Threechop soils are on rounded ridgetops and upper side-slopes of mountains. Slopes are 9 to 50 percent. Elevations are 600 to 1900 feet. These soils formed in material weathered from soft sandstone and mudstone. The climate is characterized by cool foggy summers and cool moist winters. A moderate marine influence limits the diurnal and annual range in temperature. Mean annual precipitation is 50 to 70 inches. Mean January temperature is about 49 degrees F., mean July temperature is about 56 degrees F., and the mean annual temperature is about 53 degrees F. The frost-free season is 220 to 320 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Kibesillah, Ornbaun, Yellowhound, Zeni and Vandamme soils. Kibesillah, Ornbaun, Yellowhound and Zeni soils dominantly occur on mountain sideslopes. Kibesillah and Yellowhound soils formed from hard sandstone and have loamy-skeletal particle-size control sections. Zeni and Ornbaun soils have a fine-loamy particle-size control section. Zeni soils are moderately deep. Vandamme soils occur on ridgetops and upper sideslopes of mountains in areas with a stronger marine influence than Threechop soils and have a udic soil moisture regime.
DRAINAGE AND PERMEABILITY: Well drained, surface runoff under bare soil conditions is medium to rapid; moderately slow permeability.
USE AND VEGETATION: This soil is used for commercial timber, wildlife and watershed. Vegetation consists of Douglas-fir, redwood, tanoak, huckleberry and few rhododendron.
DISTRIBUTION AND EXTENT: Northern coastal California. The series is not extensive. MLRA 4.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Mendocino County, California, Western Part, 1993.
REMARKS: The activity class was added to the classification in March of 2003. Competing series were not checked at that time. - ET
Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon -- 0-8 inches (A).
Argillic horizon -- 8 to 42 inches, (Bt1, Bt2, Bt3, Bt4, Bt5).
Paralithic contact -- Soft sandstone and mudstone occur at 42 inches. Range is 40 to 60 inches. Material slakes in water and textures to clay loam. Does not technically qualify for paralithic because of fractures but a Cr is preferred for interpretation reasons.
Mineralogy - placed in mixed mineralogy class. Lab characterization shows moderate amount of kaolinite by DTA: Bt2 = 38 percent; Bt3 = 35 percent.
Many areas mapped as Threechop soils were mapped as the Mendocino soil by the California Soil-Vegetation Survey 1947-1950.
ADDITIONAL DATA: NSSL reference sample nos. 821754 - 821759, 837350, 837351