LOCATION LATAH WA+IDEstablished Series
TAXONOMIC CLASS: Fine, mixed, superactive, mesic Xeric Argialbolls
TYPICAL PEDON: Latah silt loam, grassland. (Colors are for dry soil unless otherwise noted.)
A1--0 to 6 inches; dark grayish brown (10YR 4/2) silt loam, very
dark brown (10YR 2/2) moist; moderate fine and medium granular structure; slightly sticky and slightly plastic; many roots; many very fine pores; neutral (pH 6.8); abrupt smooth boundary. (6 to 8 inches thick)
A2--6 to 10 inches; dark grayish brown (10YR 4/2) silt loam, very dark brown (10YR 2/2) moist; weak coarse prismatic breaking to moderate fine and medium subangular blocky structure; slightly hard, very friable, slightly sticky and slightly plastic; many roots; neutral (pH 6.8); clear wavy boundary. (3 to 15 inches thick)
A3--10 to 19 inches; dark grayish brown (10YR 4/2) silt loam, very dark brown (10YR 2/2) moist; moderate fine and medium prismatic structure; slightly hard, very friable, slightly sticky and slightly plastic; many roots; many very fine pores, neutral (pH 6.8); clear wavy boundary. (8 to 10 inches thick)
E1--19 to 24 inches; light brownish gray (10YR 6/2) silt loam, dark grayish brown (10YR 4/2) moist; weak fine and medium prismatic structure; slightly hard, very friable, slightly sticky and slightly plastic; common roots; common very fine pores; neutral (pH 6.8); clear irregular boundary. (4 to 6 inches thick)
E2--24 to 30 inches; light gray (10YR 7/1) silt loam, gray (10YR
5/1) moist; massive; slightly hard, very friable, slightly sticky and slightly plastic; common roots; many very fine pores; neutral (pH 6.8); abrupt smooth boundary. (8 to 12 inches thick)
B1t--30 to 36 inches; brown (10YR 5/3) silty clay loam, dark brown (10YR 4/3) moist; strong fine and medium subangular blocky structure; hard, very firm, sticky and plastic; few flattened roots in cracks, no roots in peds; common very fine pores; thick continuous clay films on all faces of peds; few fine and medium light brown (7.5YR 6/4) and few fine and medium light gray (2.5Y 7/2) mottles on peds; organic matter staining along fracture planes; neutral (pH 6.6); clear smooth boundary. (5 to 10 inches thick)
Bt2--36 to 60 inches; brown (10YR 5/3) silty clay loam, dark brown (10YR 4/3) moist; strong fine and medium subangular blocky structure; hard, very firm, sticky and plastic; few flattened roots in cracks, no roots in peds; many very fine pores; thin continuous clay films on all faces of peds; common medium reddish yellow (7.5YR 6/6) mottles and common medium and large light gray (2.5Y 7/2) mottles on peds; organic matter stainings along fracture planes; neutral (pH 6.6).
TYPE LOCATION: Whitman County, Washington; 2,600 feet south and 600 feet west of the NE corner sec. 7, T.15N., R.46E.
RANGE IN CHARACTERISTICS: The mean annual soil temperature at a depth of 20 inches is 47 degrees to 50 degrees F. The soils are usually moist, but are dry between depths of 4 to 12 inches for 45 to 60 consecutive days in later summer and autumn. The mollic epipedon is 17 to 32 inches thick and the solum is 40 to more than 60 inches thick. The soils are neutral or mildly alkaline throughout.
The A horizon has value of 4 or 5 dry, 2 or 3 moist and chroma of 1 or 2 or moist. The A11 horizon is estimated to contain 3 to 8 percent organic matter.
The E horizon has value of 5 through 7 dry, 4 or 5 moist, and chroma of 1 or 2 dry or moist. The structure is weak prismatic or massive. In some pedons, the soil is mottled below th A11 horizon.
The B2t horizon has value of 4 through 6 dry, 3 through 5 moist and chroma of 2 or 3 moist or dry. It is silty clay loam, silty clay, or clay and have 35 to 60 percent clay. The A2 and B2t horizon have a few very fine and fine manganese concretions in some pedons.
COMPETING SERIES: These are the Quicksell and Tilma series. Quicksell soils are 20 to 40 percent sand in the particle-size control section. Tilma soils lack mottles and low chroma associated with wetness.
GEOGRAPHIC SETTING: Latah soils are on level to gently sloping bottom lands and low terraces along drainageways in undulating to steep and hilly topography. The soils formed in loess and alluvium from the surrounding loessial uplands. Elevations range from 1,800 to 3,200 feet. Summers are warm and dry, winters are cool and moist. The precipitation ranges from 18 to 23 inches. The mean January temperature
is 28 degrees F., mean July temperature is 68 degrees F., mean annual temperature is 48 degrees F., and the frost-free season is 100 to 135 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Caldwell, Garfield, Naff, Palouse, Snow and Thatuna soils. Caldwell and Snow soils have less than 35 percent clay and have an irregular decrease in organic matter. Garfield soils have an ochric epipedon. Naff and Palouse soils do not have an E horizon. Thatuna soils have less than 35 percent clay in the argillic horizon.
DRAINAGE AND PERMEABILITY: Somewhat poorly drained. Runoff is slow to ponded depending on slope gradient. Permeability is moderate in the A horizons and very slow in the Bt horizons.
USE AND VEGETATION: Cultivated and cropped to small grain. Native vegetation consisted of tufted hairgrass, sedge, rose, redosier dogwood, cow parsnips, willows, black hawthorn, saskatoon serviceberry, potentilla, rush, and scattered hardwood.
DISTRIBUTION AND EXTENT: Eastern Washington, northeastern Oregon, and northern Idaho. The soil is of moderate extent.
MLRA OFFICE RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Benewah County, Idaho, 1930.
REMARKS: Diagnostic horizons and features recognized in this pedon are a mollic epipedon from the surface to 19 inches, an albic horizon from 19 to 30 inches, and an argillic horizon from 30 to 60 inches