LOCATION MCCOMAS OREstablished Series
TAXONOMIC CLASS: Clayey-skeletal, smectitic, mesic Aquic Palexeralfs
TYPICAL PEDON: McComas very gravelly loam - pasture, on a south facing slope of 15 percent at an elevation of 1440 feet. (Colors are for moist soil unless otherwise stated.)
A--0 to 5 inches; dark brown (7.5YR 3/4) very gravelly loam, brown (7.5YR 5/4) dry; moderate very fine and fine subangular blocky structure parting to granular; slightly hard, friable, slightly sticky and slightly plastic; many very fine, fine and medium roots; many very fine and fine irregular and tubular pores; 35 percent gravel; moderately acid (pH 5.8); clear smooth boundary. (4 to 10 inches thick)
Bt1--5 to 13 inches; dark brown (7.5YR 3/4) very cobbly silty clay loam, brown (7.5YR 5/4) dry; moderate fine and medium subangular blocky structure; hard, firm, sticky and plastic; many very fine and fine, and few medium roots; many very fine and fine tubular pores; many distinct dark brown (7.5YR 3/4) clay films on faces of peds and lining pores; common worm casts; 15 percent gravel and 40 percent rounded and subangular basalt and tuffaceous sandstone cobbles; few fine faint yellowish brown (10YR 5/6) masses of iron accumulations; strongly acid (pH 5.5); abrupt smooth boundary. (6 to 15 inches thick)
2Bt2--13 to 27 inches; dark grayish brown (10YR 4/2) very cobbly clay, grayish brown (10YR 5/2) dry; weak coarse and very coarse angular blocky structure; extremely hard, extremely firm, very sticky and very plastic; common fine and medium roots along vertical faces of peds; common very fine and fine tubular pores; many prominent dark brown (7.5YR 3/4) clay films on faces of peds; 30 percent cobbles and 15 percent stones; many medium and coarse distinct yellowish brown (10YR 5/8) masses of iron accumulations; strongly acid (pH 5.5); gradual smooth boundary. (10 to 14 inches thick)
2C1--27 to 38 inches; dark grayish brown (2.5Y 4/2) very cobbly clay, grayish brown (2.5Y 5/2) dry; massive; extremely hard, extremely firm, very sticky and very plastic; few very fine roots; very few very fine tubular pores; 25 percent cobbles and 10 percent stones; many medium and coarse prominent gray (N 5/0) iron depletions, and many fine and medium and common coarse distinct strong brown (7.5YR 4/6) masses of iron accumulation; strongly acid (pH 5.5); clear smooth boundary.
2C2--38 to 63 inches; dark grayish brown (2.5Y 4/2) extremely stony clay, grayish brown (2.5Y 5/2) dry; massive; extremely hard, extremely firm, very sticky and very plastic; very few very fine tubular pores; 10 percent cobbles and 70 percent stones; many medium and coarse prominent gray (N 5/0) iron depletions, and many fine and medium and common coarse distinct strong brown (7.5YR 4/6) masses of iron accumulations; strongly acid (pH 5.5). (Combined thickness of the 2C horizon is 30 to 45 inches)
TYPE LOCATION: Douglas County, Oregon, 3 1/2 miles north of the town of Glide, about 2640 feet west and 610 north of the southeast corner of section 32, T. 25 S., R. 3 W. (Latitude 43 degrees, 20 minutes, 47 seconds N, Longitude 123 degrees, 4 minutes, 46 seconds W.)
RANGE IN CHARACTERISTICS: Depth to the clayey (2Bt) lithologic discontinuity is 13 to 25 inches. The soil is usually moist for prolonged periods during the winter and spring, but is dry within all parts of the moisture control section for 45 to 60 days following the summer solstice. The particle-size control section averages 35 to 50 percent clay and 35 to 60 percent rock fragments. The mean annual soil temperature is 52 to 56 degrees F. Stones and cobbles are scattered over the surface in varying amounts. Depth to high chroma iron accumulations is 4 to 10 inches, and depth to depletions having chroma of 2 or less is 20 to 30 inches. Base saturation is less than 75 percent throughout the profile.
The A horizon has hue of 10YR or 7.5YR, value of 2 or 3 moist, 4 or 5 dry, and chroma of 2 to 4 moist and 3 or 4 dry. It has 35 to 50 percent gravel and 0 to 10 percent cobbles.
The Bt horizon has hue of 10YR or 7.5YR, value of 3 or 4 moist, 4 or 5 dry, and chroma of 3 or 4 moist and dry. It is very cobbly silty clay loam or very cobbly clay loam, with 30 to 40 percent clay. It has 5 to 15 percent gravel and 30 to 45 percent cobbles. It is strongly acid to slightly acid.
The 2Bt horizon has hue of 2.5Y or 10YR, value of 3 or 4 moist, 4 or 5 dry, and chroma of 2 to 4 moist and dry. It is very cobbly clay, with 60 to 75 percent clay. It has 0 to 5 percent gravel, 25 to 35 percent cobbles, and 10 to 20 percent stones.
The 2C horizon has hue of 2.5Y or 10YR, value of 3 or 4 moist, 4 or 5 dry, and chroma of 2 to 4 moist and dry. It is very cobbly clay, extremely cobbly clay, or extremely stony clay, with 60 to 75 percent clay. It has 0 to 5 percent gravel, 10 to 25 percent cobbles, and 10 to 70 percent stones. It is strongly acid to slightly acid.
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING: McComas soils are on slump blocks. They formed in colluvium from basalt. Slopes are 3 to 30 percent. Elevations are 900 to 2200 feet. The climate is characterized by warm, wet winters and hot, dry summers. The mean annual temperature is 50 to 55 degrees F. and the mean annual precipitation is 40 to 60 inches. The frost free period is 160 to 200 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Climax, Curtin, Dixonville, Panther, Philomath, and Yoncalla soils. Climax and Curtin are very fine and are Vertisols. Climax soils are on convex side slopes, and Curtin soils are on concave footslopes. Dixonville soils are fine and are on convex side slopes. Panther soils are poorly drained and are on concave positions and in drainageways. Philomath soils are clayey and are on convex side slopes. Yoncalla soils are fine and are on footslopes.
DRAINAGE AND PERMEABILITY: Somewhat poorly drained; permeability is moderately slow over very slow. There is a perched water table at 0.5 to 1.5 feet from November to May.
USE AND VEGETATION: Pasture, wildlife habitat, and water supply. Native vegetation is Oregon white oak, incense cedar, Pacific poison oak, hairy honeysuckle, western snakeroot, tall Oregongrape, rose, blue wildrye, sedge, and scattered Douglas fir and ponderosa pine.
DISTRIBUTION AND EXTENT: Southwestern Oregon, MLRA 5. The series is of small extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California
SERIES ESTABLISHED: Douglas County, Oregon, 1994.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon
Argillic horizon - from 5 to 27 inches. (Bt and 2Bt horizons)
Pale feature - An abrupt clay increase of 20 percent or more at 13 inches.
Aquic feature - redox depletions with chroma of 2 or less within 30 inches of the surface (2C1 horizon 27 to 38 inches)
Base saturation is assumed to be between 35 and 75 percent in the argillic horizon.
Particle-size control section - from 5 to 25 inches, over 35 percent rock fragments and clay content averages over 35 percent