LOCATION SWEITBERG WA+OREstablished Series
TAXONOMIC CLASS: Fine, smectitic, frigid Pachic Argixerolls
TYPICAL PEDON: Sweitberg silty clay loam- cultivated on a 4 percent north-facing slope at an elevation of 3,770 feet. (Colors are for dry soil unless otherwise noted).
Ap--0 to 9 inches; dark grayish brown (10YR 4/2) silty clay loam, black (10YR 2/1) moist, moderate medium subangular blocky structure; hard, firm, moderately sticky and moderately plastic; many very fine and few fine roots; few very fine tubular and irregular pores; slightly acid (pH 6.4); abrupt smooth boundary. (5 to 18 inches thick)
Bt1--9 to 16 inches; dark grayish brown (10YR 4/2) silty clay loam, very dark brown (10YR 2/2) moist; moderate medium prismatic structure parting to moderate medium angular blocky; very hard, firm, moderately sticky and moderately plastic; common very fine roots; common very fine and fine tubular pores; few faint stress cutans on faces of peds; 5 percent gravel; neutral (pH 6.6) clear wavy boundary.
Bt2--16 to 28 inches; brown (10YR 4/3) silty clay, dark brown (10YR 3/3) moist; moderate coarse prismatic structure parting to strong medium angular blocky; very hard, firm, very sticky and very plastic, common very fine roots; common very fine and few fine tubular pores, continuous distinct stress surfaces and clay films on faces of peds and common distinct clay films lining pores; 5 percent gravel and 5 percent cobbles; neutral (pH 6.6); clear wavy boundary. (Combined thickness of the Bt horizon is 12 to 22 inches)
2Bt3--28 to 32 inches; brown (10YR 4/3) very cobbly clay, dark brown (10YR 3/3) moist ped faces dark brown (7.5YR 3/3) moist; weak coarse prismatic structure parting to strong medium angular blocky; very hard, very firm, very sticky and very plastic; few very fine roots between peds; few very fine tubular pores; continuous prominent stress surfaces and clay films on faces of peds, 15 percent gravel and 25 percent cobbles, neutral (pH 7.0) abrupt irregular boundary. (3 to 6 inches thick)
3R--32 inches; basalt.
TYPE LOCATION: Asotin County, Washington; about 2 miles south of Anatone; 30 feet south, 2,400 feet west of the northeast corner sec. 12, T. 7 N., R. 45 E.
RANGE IN CHARACTERISTICS: The solum thickness and depth to a lithic contact with basalt is 20 to 40 inches. Average annual soil temperature is about 46 degrees F. The soils are usually moist, but are dry in all parts between depths of 4 and 12 inches for 60 to 75 consecutive days during summer and fall. The particle-size control section has 35 to 50 percent clay. The upper 20 inches of the argillic horizon or the entire argillic horizon if less than 20 inches thick averages 10 to 35 percent rock fragments. The mollic epipedon is 20 to 30 inches thick and includes the upper part of the argillic horizon. Reaction is slightly acid or neutral.
The A or Ap horizon has value of 2 or 3 moist, 3 or 4 dry, and chroma of 1 or 2 dry or moist.
An AB horizon is present in some pedons.
The Bt and 2Bt horizons have hue of 7.5YR or 10YR, value of 3 through 5 dry, 2 through 4 moist and chroma of 2 or 3 dry or moist. The Bt silty clay loam, silty clay, or clay with 35 to 55 percent clay. The 2Bt horizon is very cobbly clay, very gravelly clay or gravelly silty clay with 40 to 55 percent clay.
COMPETING SERIES: These are the Arcia, Arva, Broadhead, Bumpheads (T), Cristo, Henefer, Rugar, and Schnipps (T) series. Arcia soils are dry more than 75 consecutive days. Arva, Broadhead, Henefer, Highwood, Rugar, and Schnipps soils are more than 40 inches deep. Bumpheads soils are 24 to 40 inches to a paralithic contact. Cristo soils have a calcareous C horizon that is 55 to 95 percent rock fragments above the lithic contact.
GEOGRAPHIC SETTING: Sweitberg soils are on basalt plateaus or structural benches. Slopes are 2 to 30 percent. These soils formed in loess over slope alluvium and colluvium from weathered basalt. Elevation ranges from 3,400 to 4,500 feet. Summers are warm and dry and winters are cool and moist. Average annual precipitation is typically 20 to 25 inches but ranges to 17 inches in northeastern Oregon. Average annual temperature is 42 to 45 degrees F. Frost-free season is 70 to 115 days.
GEOGRAPHICALLY ASSOCIATED SOILS: They are the Harlow and Snell soils on canyon walls. Harlow soils have basalt at a depth of less than 20 inches. Snell soils are clayey-skeletal.
DRAINAGE AND PERMEABILITY: Well drained; slow to medium runoff, slow permeability.
USE AND VEGETATION: Used for crop production, livestock grazing and wildlife habitat. The principle crops are small grains, alfalfa and grass. Native vegetation is Idaho fescue, rose, potentilla, big bluegrass and bluebunch wheatgrass.
DISTRIBUTION AND EXTENT: Southeast Washington and northeastern Oregon; MLRA 9. The series is of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Asotin County, Washington, 1984.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
mollic epipedon - from the surface to 28 inches
argillic horizon - from 9 to 32 inches
lithic contact - at 32 inches.