LOCATION MCNAB OREstablished Series
TAXONOMIC CLASS: Fine, mixed, superactive, mesic Aquic Palexeralfs
TYPICAL PEDON: McNab clay loam-forested, on a 10 percent slope at an elevation of 1900 feet. (Colors are moist unless otherwise stated.)
Oi--0.5 inch to 0; partially decomposed needles and twigs.
A--0 to 6 inches; dark brown (7.5YR 3/3) clay loam, yellowish brown (10YR 5/4) dry; moderate fine granular structure; slightly hard, friable, sticky and plastic; common very fine, fine, medium, and coarse roots; many very fine irregular pores; 1 percent gravel; very strongly acid (pH 4.6); abrupt smooth boundary. (4 to 10 inches thick)
Bt1--6 to 17 inches; dark yellowish brown (7.5YR 4/4) clay, light yellowish brown (10YR 6/4) dry; moderate fine and medium subangular blocky structure; hard, friable, sticky and plastic; common very fine, fine, medium and coarse roots; common very fine tubular pores; common faint clay films on faces of peds and in pores; 1 percent gravel; very strongly acid (pH 4.8); clear wavy boundary.
Bt2--17 to 42 inches; yellowish brown (10YR 5/6) clay, yellowish brown (10YR 5/8) dry; moderate medium angular blocky structure; hard, firm, very sticky and very plastic; few very fine roots; common very fine tubular pores; common prominent clay films on faces of peds and in pores; 1 percent gravel; many medium distinct brown (10YR 5/3, strong brown (7.5YR 5/8) masses of iron accumlation and grayish brown (2.5Y 5/2) iron depletions, many prominent black (10YR 2/1) manganese stains; strongly acid (pH 5.2); gradual wavy boundary.
Btg--42 to 60 inches; light olive brown (2.5Y 5/4) silty clay, light brownish gray (2.5Y 6/2) dry; moderate medium angular blocky structure; hard, firm, very sticky and very plastic; few very fine roots; common very fine tubular pores; many distinct clay films on faces of peds and in pores; 1 percent gravel; many coarse prominent dark yellowish brown (10YR 4/6), and common coarse prominent strong brown (7.5YR 5/8) masses of iron accumulation, common prominent black (10YR 2/1) manganese stains; strongly acid (pH 5.4). (Combined thickness of the Bt horizon is 50 to 56 inches)
TYPE LOCATION: Douglas County, Oregon, 5 miles south of the town of Camas Valley, 600 feet north and 1900 feet east of the southwest corner of section 17, T. 30 S., R. 9 W., W.M. (Latitude 42 degrees, 57 minutes, 19 seconds N, Longitude 123 degrees, 40 minutes, 26 seconds W)
RANGE IN CHARACTERISTICS: The depth to bedrock and solum thickness is greater than 60 inches. The mean annual soil temperature is 53 to 56 degrees F. The soil is usually moist but is dry within all parts of the moisture control section for 45 to 60 days following the summer solstice. It has 0 to 10 percent gravel. Depth to mottles having chroma of 2 or less is 15 to 25 inches.
The A horizon has a value of 2 or 3 moist, 4 to 5 dry, and chroma of 2 to 4 moist and dry. It is very strongly to slightly acid.
The Bt horizon has hue of 7.5YR or 10YR, value of 4 to 6 moist, 5 to 7 dry, and chroma of 4 to 8 moist and dry. It is clay loam, silty clay or clay with 35 to 50 percent clay. Mottles have hue of 7.5YR and 2.5Y, value of 5 or 6, and chroma of 2 to 8. It is very strongly or strongly acid. Base saturation by sum is 35 to 60 percent.
The Btg horizon has matrix hue of 2.5Y, value of 4 or 5 moist, 5 or 6 dry and chroma of 3 or 4 moist and 2 or 3 dry. Mottles have hue of 10YR or 7.5YR, value of 4 or 5 and chroma of 6 or 8. It is silty clay or clay. It is very strongly or strongly acid. Base saturation by sum is 35 to 60 percent.
COMPETING SERIES: These are the Coveland, Coweeman, Hardscrabble, Prather, Sara, and Scamman series. Coveland and Scamman soils have an albic horizon that interfingers into the argillic horizon. Coweeman soils are on terraces and have hue of 5GY to 2.5Y in the Btg horizon and have mottles at 5 to 7 inches from the surface. Sara and Prather soils have an umbric epipedon. Hardscrabble soils have an abrupt boundary between the BA and 2Bt horizons and lack the 7.5YR or redder mottles in the argillic horizon.
GEOGRAPHIC SETTING: McNab soils are in upland swales. They formed in residuum and colluvium from sedimentary rock. Slopes are 0 to 20 percent. Elevations are 1000 to 2500 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 55 inches. The frost free period is 120 to 210 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Atring, Bellpine, Vermisa, and Windygap soils. Atring and Vermisa soils are loamy-skeletal and are on adjacent more steeply sloping positions. Bellpine and Windygap soils are well drained and are on convex positions.
DRAINAGE AND PERMEABILITY: Somewhat poorly drained; slow permeability; There is a water table at 1.5 to 3.0 feet from November through May.
USE AND VEGETATION: McNab soils are used for timber production, watershed and wildlife habitat. Natural vegetation is Douglas fir, ponderosa pine, sugar pine, grand fir, Pacific madrone, golden chinkapin, salal, western swordfern, hairy honeysuckle, American trailplant, rose, western fescue and California fescue.
DISTRIBUTION AND EXTENT: Southwestern Oregon, MLRA 5. The series is inextensive.
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 6 to 60 inches. (Bt1, Bt2, and Btg horizons)
Pale feature - percentage of clay does not decrease from its maximum amount by 20 percent or more within a depth of 60 inches from the soil surface and many coarse mottles having chroma of 6 at 42 inches.
Aquic subgroup - Mottles that have chroma of 2 or less occur at 17 inches.
Ultic subgroup - base saturation is less than 75 percent throughout the argillic horizon.
Mollic subgroup - color value moist of 3 from 0 to 6 inches and contains over 0.7 percent organic carbon.
Particle-size control section - from 6 to 26 inches. (Bt1 and Bt2 horizons), and contains over 40 percent clay.
The superactive cation exchange activity class was added to the classification in 10/2005. The competing series section was not updated at that time. Last revision 3/1995.