LOCATION SOUTHWORTH ORTentative Series
TAXONOMIC CLASS: Loamy-skeletal, isotic, frigid Vitrandic Argixerolls
TYPICAL PEDON: Southworth ashy loam on a north-facing, forested side slope at an elevation 1403 meters (4804 feet). (Colors are for dry soil unless otherwise noted. When described on September 9, 2006, the soil was dry throughout.)
Oi--0 to 8 centimeters (0 to 3 inches); slightly decomposed fir needles, elk sedge, moss, and twigs.
A--8 to 15 centimeters (3 to 6 inches); dark gray (10YR 4/1) channery ashy loam, black (10YR 2/1) moist; weak fine granular structure; soft, moderately sticky and moderately plastic; many fine and very fine roots; common fine pores; l0 percent (2 to 75 mm) channers and 5 percent (75 to 150 mm) channers; neutral (pH 7.3); clear wavy boundary. (8 to 25 centimeters (3 to 10 inches) thick)
ABt--15 to 33 centimeters (6 to 13 inches); brown (10YR 5/3) very channery ashy silt loam, very dark grayish brown (10YR 3/2) moist; weak fine granular structure; slightly hard, friable, moderately sticky and moderately plastic; common coarse, medium and fine roots; common fine pores; few discontinuous distinct clay films on ped faces, especially adjacent to rock fragments; 20 percent (2 to 75 mm) channers and 15 percent (75 to 150 mm) channers; neutral (pH 6.6); gradual wavy boundary. (0 to 25 centimeters (0 to 10 inches) thick)
Bt--33 to 81 centimeters (13 to 32 inches); yellowish brown (10YR 5/4) extremely channery silty clay loam, dark yellowish brown (10YR 3/4) moist; weak fine and very fine subangular blocky structure; hard, firm, moderately sticky and moderately plastic; common very fine, fine, and medium roots; common fine pores; few discontinuous distinct clay films on ped faces, especially adjacent to rock fragments; 10 percent (250 to 600 mm) flagstones and stones, 25 percent (75 to 250 mm) channers and flagstones, 25 percent (2 to 75 mm) channers; neutral (pH 7.2); gradual wavy boundary. (43 to 64 centimeters (17 to 25 inches) thick)
R--81 centimeters (32 inches); highly fractured, hard shale with less than 5 percent soil material between fractures. The shale layers have been faulted and tipped from the horizontal.
TYPE LOCATION: About 8 kilometers (5 miles) southwest of Seneca, Oregon on US 395, through Soda Valley on a farm road on the east side of US 395; 44 degrees, 6 minutes, 11.4 seconds north, 118 degrees, 57 minutes, 4.8 seconds west; UTM 11 0343826 and 4805184 on the Silvies USGS quadrangle.
RANGE IN CHARACTERISTICS: The solum is 50 to 100 centimeters (20 to 40 inches) thick and extends to a lithic contact. Mean annual soil temperature is 6 to 8 degrees C. (42 to 47 degrees F.). These soils are usually moist, but are dry in all parts between depths of 10 to 31 centimeters (4 and 12 inches) for 60 to 90 consecutive days following the summer solstice. Organic matter content decreases to less than one percent above a depth of 50 centimeters (20 inches). The particle-size control section averages 18 to 35 percent clay and 5 to 25 percent sand in the fine earth fraction. Rock fragments consist of channers and flagstones from shale or mudstone. Base saturation ranges from 75 to 85 percent.
The A horizon has dominant hue of 10YR, but may include 7.5YR, value of 2 or 3 moist, 4 or 5 dry and chroma of 1 to 3 moist or dry. It is ashy loam with 18 to 27 percent clay and 10 to 65 percent channers and flagstones. It has 5 to 15 percent volcanic glass and 0.4 to 0.8 percent acid-oxalate extractable aluminum plus one-half iron. Soil reaction is neutral or slightly acid.
The ABt horizon, when present, has hue of 7.5YR or 10YR and chroma of 2 or 3 moist or dry. Texture is ashy silt loam or ashy loam and has 10 to 50 percent channers and flagstones. It averages 18 to 27 percent clay. It has 5 to 15 percent volcanic glass and 0.4 to 0.8 percent acid-oxalate extractable aluminum plus one-half iron. Soil reaction is neutral or slightly acid.
The Bt horizon has hue of 5YR, 7.5YR, or l0YR, value of 3 or 4 moist, 4 to 6 dry, and chroma of 2 to 4 moist or dry. Texture is dominantly silty clay loam, but includes silt loam and clay loam. It averages 25 to 35 percent clay and 35 to 70 percent flagstones and channers. Soil reaction is neutral to moderately acid.
COMPETING SERIES: These are the Klickson, Larabee, Litbridge (T), Millerflat, Raycreek (T), Sycreek, and Stemilt series. All these soils lack channers and flagstones. Klickson, Litbridge, Millerflat, Sycreek, and Stemilt soils are more than 40 inches deep. Larabee soils are dry for 45 to 60 consecutive days and have acid-oxalate extractable aluminum plus one-half iron of 0.8 to 1.5 percent
GEOGRAPHIC SETTING: Southworth soils are on back slopes of hills and mountains at an elevation of 1219 to 1890 meters (4,000 to 6,200 feet). At higher elevations, Southworth soils are only found on south slopes. Slopes are 0 to 90 percent. The soils formed in slope alluvium and colluvium derived from shale and mudstone with an influence of Mazama volcanic ash in the surface. Summers are hot and dry and winters are cold and wet. Mean annual precipitation is 38 to 100 centimeters (15 to 40 inches). Mean January temperature is -4 to -3 degrees C. (24 to 27 degrees F.); mean July temperature is 17 to 19 degrees C. (63 to 67 degrees F.); and mean annual temperature is 4 to 7 degrees C. (40 to 45 degrees F.). Frost-free period is 60 to 120 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the shale derived soils of Piersonte, Logdell, and Laycock. Piersonte soils are on forested footslopes, are deep or very deep to fractured shale, and lack an argillic horizon. The Laycock soils are on forested ridgetops and benches and are shallow to fractured shale. The Logdell soils are on mountain mahogany ridgetops or adjacent to exposed shale bedrock on hillsides and are very shallow to fractured shale.
DRAINAGE AND PERMEABILITY: Well drained, slow to rapid runoff; moderately slow permeability.
USE AND VEGETATION: Timber production, livestock grazing, and wildlife habitat. Native vegetation is an open stand of ponderosa pine on the south-facing slopes and Douglas-fir on the north-facing slopes.
DISTRIBUTION AND EXTENT: East central Oregon, MLRA 43C. The series is of limited extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon, MO-1
SERIES PROPOSED: Grant County, Oregon, 2006. The name is derived from Southworth Ranch, Ditch, and Cemetery, on the Seneca USGS quadrangle.
REMARKS: Diagnostic horizons and features recognized are:
Mollic epipedon - from 8 to 33 Centimeters (3 to 13 inches) (A and ABt horizons)
Argillic horizon - from 15 to 81 centimeters (6 to 32 inches) (ABt and Bt horizons)
Lithic contact at 81 centimeters (32 inches).
Vitrandic feature - from 8 to 33 centimeters (3 to 13 inches) (A and ABt horizons)
Soil moisture regime - xeric
The Vitrandic feature and base saturation are based on lab data from an associated soil; Piersonte, S97OR-023-028.