LOCATION ONYX WA+ID+OREstablished Series
TAXONOMIC CLASS: Coarse-silty, mixed, superactive, mesic Cumulic Haploxerolls
TYPICAL PEDON: Onyx silt loam - cultivated. (Colors are for moist soil unless otherwise stated. All textures are apparent field textures).
Ap--0 to 8 inches; very dark brown (10YR 2/2) silt loam, dark grayish brown (10YR 4/2) dry; weak fine granular structure; soft, very friable, slightly sticky and slightly plastic; many roots; many very fine and fine irregular pores; neutral (pH 6.8); abrupt smooth boundary. (0 to 10 inches thick)
A1--8 to 30 inches; very dark grayish brown (10YR 3/2) silt loam, grayish brown (10YR 5/2) dry; massive; soft, very friable, slightly sticky and slightly plastic; common roots; many very fine tubular pores; neutral (pH 7.0); clear smooth boundary. (8 to 30 inches thick)
A2--30 to 46 inches; dark brown (10YR 3/3) silt loam, brown (10YR 5/3) dry; massive; soft, very friable, slightly sticky and slightly plastic; common roots; many very fine tubular pores; neutral (pH 7.0); clear smooth boundary. (10 to 20 inches thick)
C--46 to 60 inches; dark grayish brown (10YR 4/2) silt loam, brown (10YR 5/3) dry; massive; slightly hard, friable; few roots; many very fine tubular pores; neutral (pH 7.2).
TYPE LOCATION: Adams County, Washington; 1,000 feet north and 100 feet west of southeast corner section 29, T. 16 N., R. 38 E.
RANGE IN CHARACTERISTICS: Average annual soil temperature is 50 to 55 degrees F. These soils are usually moist but are dry in all parts between depths of 4 and 12 inches for 90 to 105 consecutive days following the summer solstice. The mollic epipedon is 20 to more than 40 inches thick. The particle-size control section is dominantly silt loam, but in many pedons there are thin lenses (less than 1 inch) of very fine sandy loam, fine sandy loam, sandy loam, or medium sand; however, the weighted average texture is silt loam, which has 10 to 18 percent clay and less than 15 percent coarser than very fine sand. The soils are neutral or slightly alkaline.
The A horizon has value of 2 or 3 moist, 4 or 5 dry and chroma of 1 to 3 moist and 1 through 5 dry.
The B horizon, when present, has value of 2 or 3 moist, 4 or 5 dry and chroma of 2 or 3 moist and 2 to 5 dry.
The C horizon below 40 inches ranges widely in color. Textures range from silt loam to very gravelly sandy loam.
COMPETING SERIES: These are the
Covello soils dry for 60 to 90 consecutive days following the summer solstice; moderately alkaline or strongly alkaline throughout; calcareous in the lower part of the particle-size control section
Hermiston soils dry for 70 to 90 consecutive days following the summer solstice; moderately alkaline and calcareous in the C horizons
Mondovi soils dry for 60 to 75 consecutive days following the summer solstice
Pedigo soils dry for 60 to 75 consecutive days following the summer solstice; effervescent throughout and are moderately or strongly alkaline; 30 to 40 inches to aquic moisture regime (somewhat poorly drained)
Powder soils dry for 90 to 120 consecutive days following the summer solstice; calcareous in some part above 43 inches
Touchet soils - dry for 75 to 90 consecutive days following the summer solstice; redoximorphic features in lower part of the particle-size control section (moderately well drained)
GEOGRAPHIC SETTING: These soils are on flood plains and on alluvial fans in the mouth of large draws tributary to the major streams. In most places, they are subject to flooding once or twice in 10 years. The alluvium is more than 40 inches deep over contrasting material. The elevation ranges from 400 to 3,400 feet. The average annual precipitation ranges from 12 to 16 inches with warm, dry summers and cool, moist winters. The average January temperature is 32 degrees F., and average July temperature is 71 degrees F. The mean annual temperature is 48 to 53 degrees F. The frost-free season is 120 to 170 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Ahtanum, Condon, Mikkalo, Oliphant, Umapine, and Walla Walla soils. Ahtanum soils are in basins and have a weakly cemented pan at depths of less than 40 inches. Condon, Mikkalo, Oliphant, and Walla Walla soils are on uplands and have a regular decrease in organic carbon in the particle-size control section. Also Condon and Mikkalo soils are 20 to 40 inches deep to a lithic contact. Umapine soils are in basins and are strongly saline and alkaline.
DRAINAGE AND PERMEABILITY: Well-drained; slow runoff; moderate permeability. Occasional floods recede rapidly.
USE AND VEGETATION: Production of dryland small grains and peas. Irrigated alfalfa hay and climatically adapted row crops. Natural vegetation is bluebunch wheatgrass, basin wildrye, and basin big sagebrush.
DISTRIBUTION AND EXTENT: Southeastern Washington, eastern Oregon, and southern Idaho; MLRA 8. It is moderately extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Portneuf Area, Bannock County, Idaho, 1918.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon from the surface to 46 inches
Cumulic feature organic carbon is assumed to have an irregular decrease with depth
Particle-size control section the zone from 10 to 40 inches (parts of A1 and A2 horizons).