LOCATION TARKIO MTEstablished Series
TAXONOMIC CLASS: Very-fine, mixed, superactive, frigid Typic Palexeralfs
TYPICAL PEDON: Tarkio silty clay loam - native cover. (Colors are for dry soil unless otherwise noted.)
0i--0 to 2 inches; pine needles, leaves and twigs and a humus layer of decayed forest litter.
E--2 to 7 inches; pinkish gray (7.5YR 6/2) silty clay loam, brown (7.5YR 5/2) moist; moderate thick platy structure separating to moderate fine subangular blocks; slightly hard, friable, moderately sticky, moderately plastic; many fine and medium roots; common fine tubular pores and medium vesicles; surfaces of peds have glazed appearance when dry; insides of peds have threadlike net pattern with reddish brown color; slightly acid (pH 6.1); gradual boundary. (2 to 8 inches thick)
B/E--7 to 11 inches; pinkish gray (5YR 6/2) silty clay, reddish brown (5YR 4/3) moist; strong fine angular blocky structure; very hard, firm, moderately sticky, moderately plastic; many fine and medium roots; common fine tubular pores; dry block surfaces have glazed appearance and are coated several grains thick with gray (5YR 6/1) clear unstained silt; slightly acid (pH 6.2); clear wavy boundary. (2 to 6 inches thick)
Bt--11 to 36 inches; weak red (2.5YR 5/2) clay, reddish brown (2.5YR 4/4) moist; strong medium prismatic structure separating to strong medium and coarse angular blocks, many with pressure faces and some concave surfaces have continuous clay film of very thin to medium thickness in rippled patterns; extremely hard, very firm, moderately sticky, moderately plastic; common fine and medium roots distributed through soil in upper few inches and concentrated between faces of peds throughout horizon; common fine and very fine tubular pores in upper few inches and few below; many threadlike drifts of clear unstained silt on faces of peds in upper part; soil in lower part of horizon has a fine horizontally layered color pattern of pale red with pinkish gray dry and weak red with reddish brown (moist); slightly acid (pH 6.1 to 6.5); clear boundary. (15 to 30 inches thick)
C--36 to 60 inches; pinkish gray (5YR 7/2) with bands of weak red (2.5YR 4/2) varved clay, reddish gray (2.5YR 5/1), brown (7.5YR 5/4), and light brown (7.5YR 6/4) moist; massive except for vertical cleavages 4 to 8 inches apart; extremely hard, very firm and friable, moderately sticky, moderately plastic; 80 percent clay varves and 20 percent silty clay loam in layers ranging from 1/32 inch to 2 inches thick; nonporous; concentration of few to common roots in vertical cleavages through soil and few concentrated horizontally between layers of clay and silty clay loam; few pressure faces on walls of vertical cleavages through clay layers; calcareous; moderately alkaline (pH 7.9).
TYPE LOCATION: Missoula County, Montana; 50 feet south and 50 feet east of W1/4 corner sec. 16, T.15N., R.22W.
RANGE IN CHARACTERISTICS: The clay type is mixed, containing mica, kaolinite, chlorite and montmorillonite and having cation exchange capacities ranging from 25 to 38 millequivalents per 100 grams of clay. Percent base saturation ranges above 95 and the soils are moderately to slightly acid in the solum and neutral to slightly alkaline in the C horizons. Tarkio soils have mean annual temperature ranging from 42 to 46 degrees F. and average summer soil temperatures ranging from 59 to 62 degrees F. in cultivated fields. The soils are usually moist but the B and C horizons are dry in late summer and early fall from about July 20 to October 1. Hue ranges from 5YR through 10R. The E horizon has value of 6 or 7 dry, 3 through 5 moist and chroma of 1 or 2. The B horizon has value of 5 or 6 dry, 4 or 5 moist and chroma of 2 or 3. It is clay with from 60 to 80 percent clay and less than 15 percent fine and coarser sands. There are few to many varves of light gray silt to silty clay 1/4 inch to 2 inches thick occurring throughout the lower part of the profile starting in lower B horizons.
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING: Tarkio soils are on glacial lake terraces in the intermountain valleys of the northern Rocky mountains. Slope are 0 to 30 percent. The climate is subhumid continental. The mean annual precipitation ranges from 15 to 20 inches, half of which falls during May through September and one-third falling in May and June. Average snowfall ranges from 3 to 6 feet. Mean annual temperature ranges from 40 to 45 degrees F. Average summer temperature ranges from 64 to 67 degrees F. and average winter temperature ranges from 22 to 26 degrees F.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Greenough, Lubrecht and Yourame soils. These are timbered soils on ancient lacustrine plains and on Wisconsin Age alpine valley glacial till plains, and all have argillic horizons with less than 60 percent clay.
DRAINAGE AND PERMEABILITY: Well drained; very slow permeability.
USE AND VEGETATION: Principal use is for production of small grains, and grass pasture with smaller use for forest products. The natural vegetation is western yellow pine with understory of shrubs.
DISTRIBUTION AND EXTENT: Tarkio soils are inextensive in intermountain valleys of the northern Rocky Mountains.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: St. Regis-Ninemile Area, Missoula County, Montana, 1970.