LOCATION BENCO WAEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, mesic Typic Haploxerolls
TYPICAL PEDON: Benco cobbly silt loam, grassland. (Colors are for dry soil unless otherwise stated.)
A1--0 to 10 inches; grayish brown (10YR 5/2) cobbly silt loam, very dark grayish brown (10YR 3/2) moist; weak fine granular structure; slightly hard, friable, slightly sticky and slightly plastic; common fine roots, common fine pores; 20 percent cobbles, 10 percent gravel; neutral (pH 6.8); clear wavy boundary. (8 to 14 inches thick)
B2--10 to 20 inches; pale brown (10YR 6/3) very cobbly silt loam, dark brown (10YR 3/3) moist; weak fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common fine roots; 30 percent pebbles, 25 percent cobbles; neutral (pH 7.0); abrupt wavy boundary. (8 to 14 inches thick)
C--20 to 60 inches; extremely gravelly loamy coarse sand, single grained; loose, 80 percent pebbles, 10 percent cobbles; some rock fragments have a white silica coating on the lower side; neutral (pH 7.0).
TYPE LOCATION: Lincoln County, Washington; 80 feet east, 1,360 feet north of the southwest corner of sec. 15, T. 24 N., R. 35 E.
RANGE IN CHARACTERISTICS: The solum is 16 to 28 inches thick. The mollic epipedon is 8 to 14 inches thick. The mean annual soil temperature at a depth of 20 inches is 50 degrees to 55 degrees F. These soils are usually moist, but are dry in all parts between depths of 8 and 25 inches for 70 to 90 consecutive days. The control section contains more than 35 percent rock fragments.
The A horizon has a dry value of 4 or 5, and a chroma of 2 or 3. The structure is weak granular or blocky. It is cobbly silt loam; stony loam or gravelly loam.
The B horizon has value of 5 or 6 dry and 3 or 4 moist. It is silt loam or loam and is less than 50 percent fine sand or coarser, 5 to 18 percent clay, more than 45 percent silt and has 40 to 60 percent coarse fragments. The structure is weak subangular blocky or weak prismatic.
The C horizon is loamy coarse sand or coarse sand with 35 to 90 percent rounded rock fragments dominated by pebble size fragments.
COMPETING SERIES: These are the Brief, Clint, Garrison, Kilburn, and Speigle series. Brief and Speigle soils lack sandy-skeletal texture within depths of 20 to 40 inches. Garrison soils are dry 45 to 75 consecutive days in the moisture control section. Clint soils have bedrock at a depth of 20 to 40 inches. Kilburn soils have a sandy loam B horizon with less than 45 percent silt.
GEOGRAPHIC SETTING: Benco soils are on terraces and terrace escarpments at elevations of 1,900 to 2,500 feet. Slopes are 0 to 30 percent. The soils formed in glacial outwash materials with a mixture of loess in the upper part. Summers are hot and dry and winters are cool and moist. Mean annual precipitation is 12 to 18 inches. Mean July temperature is 73 degrees F., mean January temperature is 32 degrees F., mean annual temperature is about 52 degrees F., and the frost-free season is 110 to 160 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Anders, Bakeoven, Benge, Cheney, and Tucannon soils. Anders and Tucannon soil have bedrock at a depth of 20 to 40 inches. Bakeoven soils have bedrock at a depth of 4 to 12 inches. Benge and Cheney soils have a strongly contrasting particle size control section.
DRAINAGE AND PERMEABILITY: Well drained; slow to medium runoff; moderately rapid permeability to a depth of 20 inches and very rapid below 20 inches.
USE AND VEGETATION: Used for grazing. Native vegetation is mostly bluebunch wheatgrass, Sandberg bluegrass, and Idaho fescue.
DISTRIBUTION AND EXTENT: Eastern Washington, this series is of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Lincoln County, Washington, 1978.