LOCATION POWER IDEstablished Series
TAXONOMIC CLASS: Fine-silty, mixed, superactive, mesic Xeric Calciargids
TYPICAL PEDON: Power silt loam - on a nearly level terrace in rangeland. (Colors are for air-dry soil unless otherwise noted.)
A--0 to 9 inches; light brownish gray (10YR 6/2) silt loam, dark grayish brown (10YR 4/2) moist; weak to moderate thin platy structure parting to weak very fine granular; slightly hard, very friable, slightly sticky and slightly plastic; common roots; fine vesicular pores; few fine soft dark brown concretions in lower part; neutral (pH 6.8); clear smooth boundary. (4 to 14 inches thick)
Bt--9 to 21 inches; pale brown (10YR 6/3) silt loam, brown (10YR 4/3) moist; light gray silt coats on upper parts of prisms; weak to moderate medium prismatic structure parting to strong fine and medium subangular blocky; very hard, friable, moderately sticky and slightly plastic; common very fine roots; few very fine pores; distinct nearly continuous brown (10YR 5/3) clay films on faces of peds; few very fine dark brown concretions; slightly alkaline (pH 7.8); clear wavy boundary. (7 to 23 inches thick)
Btk--21 to 27 inches; pale brown (10YR 6/3) silt loam, brown (10YR 5/3) moist; weak to moderate medium subangular blocky structure; hard, friable, moderately sticky and moderately plastic; few fine roots; few very fine pores; common faint clay films on faces of peds; few fine threads and coatings of segregated calcium carbonate; moderately alkaline (pH 8.3); clear wavy boundary. (3 to 8 inches thick)
Bk1--27 to 31 inches; very pale brown (10YR 7/3) silt loam, pale brown (10YR 6/3) moist; massive; slightly hard, friable, moderately sticky and moderately plastic; few fine roots; few very fine pores; many threads and splotches of segregated calcium carbonate; strongly effervescent; moderately alkaline (pH 8.0); clear wavy boundary.
Bk2--31 to 46 inches; very pale brown (10YR 7/3) silt loam, pale brown (10YR 6/3) moist; massive; slightly hard, very friable, slightly sticky and slightly plastic; threads of segregated calcium carbonate; moderately effervescent; slightly alkaline (pH 8.4); clear smooth boundary. (Combined Bk horizon - 15 to 35 inches thick)
2Bk3--46 to 60 inches; very pale brown (10YR 7/3) stratified fine sandy loam and loam, brown (10YR 5/3) moist; massive; slightly hard, friable,. nonsticky and nonplastic; threads of segregated calcium carbonate; slightly effervescent; strongly alkaline (pH 8.5).
TYPE LOCATION: Gem County, Idaho; 2/3 mile southwest of Cooper School; northeast 1/4, northwest 1/4, northwest 1/4, section 22, T. 7 N., R. 3 W.; USGS Letha Quadrangle.
RANGE IN CHARACTERISTICS:
Depth to lithologic discontinuity - 30 to 60 inches or more
Depth to bedrock - more than 60 inches
Average annual soil temperature - 47 to 55 degrees F.
Particle-size control section - averages less than 15 percent sand coarser than very fine sand; 24 to 35 percent clay
Depth to calcium carbonate - 11 to 37 inches
BA horizons are present in some pedons
Moisture control section - moist less than 90 consecutive days when the soil temperature is greater than 47 degrees F.
A horizon
Hue - 2.5Y or 10YR
Value - 5 through 7 dry, 3 or 4 moist
Chroma - 2 to 4 dry or moist
Reaction - neutral or slightly alkaline
Bt horizon
Value - 5 through 7 dry, 3 through 5 moist
Chroma - 3 or 4 dry or moist
Texture - L, SIL, CL, or SICL
Clay content - 24 to 35 percent
Reaction - neutral through moderately alkaline
Btk horizon
Value - 6 or 7 dry, 4 or 5 moist
Chroma - 3 or 4 dry or moist
Texture - SIL, SICL, L or CL
Clay content - 24 to 35 percent
Calcium carbonate equivalent - 1 to 5 percent
Reaction - slightly alkaline or moderately alkaline
Bk1 and Bk2 horizons
Value - 6 through 8 dry, 4 through 7 moist
Chroma - 2 through 4 dry or moist
Texture - SIL or L
Clay content - 18 to 27 percent
Calcium carbonate equivalent - 15 to 30 percent
Reaction - slightly alkaline through strongly alkaline
2Bk3 horizon
Value - 6 through 8 dry, 4 through 7 moist
Chroma - 2 through 4 dry and moist
Texture - SIL, L, VFSL or FSL
Clay content - 8 to 20 percent
Gravel - 0 to 10 percent
Calcium carbonate equivalent - 1 to 15 percent
Reaction - slightly alkaline through strongly alkaline
2Bkq horizon - present in some pedonswith u to 20 percent durinodes
Small amounts of gypsum maybe present in the lower part of some pedons.
COMPETING SERIES: These are the Greenleaf and Larwood series. Greenleaf soils have dense laminated silt lake sediments at 12 to 40 inches. Larwood soils have 25 to 40 calcium carbonate equivalent in the argillic horizon.
GEOGRAPHIC SETTING: Power soils are on lava flow troughs and buttes on lava plains and shield volcanoes and old stream terraces in valleys. Slopes are 0 to 15 percent. Elevations range from 2,000 to 4,800 feet. These soils formed in silty alluvium from loess and weathered valcanic ash over loamy alluvium from igneous materials. The climate is semi-arid with cool moist winters and hot dry summers. The frost-free period is 100 to 160 days. Average annual precipitation is 8 to 12 inches, including up to 3 feet of snow. Average annual temperature is 45 to 53 degrees F.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Chilcott, Jenness, Lanktree, Lolalita, Owinza, and Purdam soils. Chilcott, Owinza, and Lanktree soils have Bt horizons containing more than 35 percent clay, and Chilcott soils have duripans. Jenness and Lolalita soils lack argillic horizons. Purdam soils have a weakly expressed duripan above 40 inches. These soils all occur on landscape positions similar to Power soils.
DRAINAGE AND PERMEABILITY: Well drained, slow or medium runoff; moderately slow permeability.
USE AND VEGETATION: Power soils are used mainly for rangeland and irrigated cropland. Principal crops are small grains, potatoes, sugar beets, beans, and alfalfa hay. Potential vegetation in the natural plant community is Wyoming big sagebrush, Thurber needlegrass, and bluebunch wheatgrass with basin big sagebrush in some areas.
DISTRIBUTION AND EXTENT: Southwestern and south-central Idaho; MLRA 11. The soil is moderately extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Gem County, Idaho, 1949.
REMARKS: Diagnostic horizons and other features recognized in this pedon are:
Ochric epipedon - The zone from 0 to 9 inches (the A horizon)
Argillic horizon - The zone from 9 to 27 inches (the Bt and Btk horizons)
Calcic horizon - The zone from 27 to 46 inches (the Bk1 and Bk2 horizons)
Particle-size control section - The zone from 9 to 27 inches (the argillic horizon)
Soil moisture regime - aridic bordering xeric
The term silty alluvium used in this series concept infers a localized influence on the mixed loess and weathered ash mantle by overland flow of running water.
Revisions to the pedon description in this draft as of 4/00 reflect those needed to agree with the official type location in the Gem County Area soil survey.