LOCATION DOWNEY IDEstablished Series
TAXONOMIC CLASS: Coarse-loamy over sandy or sandy-skeletal, mixed, superactive, frigid Calcic Haploxerolls
TYPICAL PEDON: Downey gravelly silt loam - on a nearly level slope in rangeland seeded to crested wheatgrass at 4,820 feet elevation. (Colors are for dry soil unless otherwise stated. When described the soil was dry to 32 inches and slightly moist below.)
A--0 to 3 inches; brown (10YR 5/3) gravelly silt loam, very dark grayish brown (10YR 3/2) moist; weak coarse platy structure parting to weak fine granular; slightly hard, very friable, slightly sticky and slightly plastic; many very fine and few fine roots; many very fine interstitial pores; about 15 percent pebbles and a few cobbles; neutral (pH 7.0); abrupt smooth boundary. (3 to 12 inches thick)
AB--3 to 12 inches; brown (10YR 5/3) gravelly silt loam, dark brown (10YR 3/3) moist; weak coarse and medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine and few fine roots; few fine and very fine tubular pores; about 15 percent pebbles and a few cobbles; neutral (pH 7.2); abrupt smooth boundary. (0 to 10 inches thick)
Bk1--12 to 17 inches; very pale brown (10YR 7/3) gravelly silt loam, brown (10YR 5/3) moist; weak medium and fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine and few fine roots; few very fine tubular pores; about 15 percent pebbles and a few cobbles; violently effervescent; mildly alkaline (pH 7.7); abrupt wavy boundary. (0 to 13 inches thick)
2Bk1--17 to 32 inches; multicolored extremely gravelly coarse sand; massive; common very fine roots; about 60 percent pebbles and 15 percent cobbles; violently effervescent and weakly cemented with lime (calcium carbonate); moderately alkaline (pH 7.9); gradual wavy boundary. (4 to 15 inches thick)
2Bk2--32 to 47 inches; multicolored extremely gravelly coarse sand; single grain; alternating and irregular layers of strongly effervescent weakly cemented material and layers of loose material with thick lime coats only on the undersides of the gravel and cobbles; about 75 percent pebbles and 10 percent cobbles; moderately alkaline (pH 8.2); diffuse irregular boundary. (14 to 39 inches thick)
2Bk3--47 to 60 inches; multicolored extremely gravelly coarse sand; single grain; about 75 percent pebbles and 10 percent cobbles; thick lime coats on the undersides of the pebbles and cobbles; moderately alkaline (pH 8.0).
TYPE LOCATION: Bannock County, Idaho; about 2 miles northwest of Downey; 445 feet south and 830 feet east of the northwest corner, sec. 20, T. 11 S., R. 37 E.
RANGE IN CHARACTERISTICS:
Average annual soil temperature - 44 to 47 degrees F.
Depth to strongly contrasting textures - to 20 inches
Thickness of mollic epipedon - 8 to 15 inches
A horizon
Color value, dry - 4 or 5
Value, moist - 2 or 3
Chroma, dry or moist - 2 or 3
Reaction - neutral or mildly alkaline
Bk horizon (if present)
Color value, dry - 7 or 8
Value, moist - 4 to 6
Chroma, dry or moist - 2 or 3
Coarse fragments - 15 to 30 percent (by volume)
Reaction - mildly or moderately alkaline
Effervescence - strong or violent
2Bk horizon
Rock fragments - 55 to 80 percent, dominantly pebbles
Cementation (slakes in water) - weakly cemented in the upper part or in irregular layers in the lower part
Effervescence - slight to violent effervescence above about 60 inches and often non-effervescent below
COMPETING SERIES: This is the Arimo (T) series. Arimo (T) soils are moderately deep to gravel and sand.
GEOGRAPHIC SETTING: Downey soils are on level to gently sloping terraces. Slopes range from 0 to 8 percent. Elevations range from 4,600 to 4,900 feet. The soils formed in silty alluvium overlying alluvial gravel and sand of mixed mineralogy. The climate is semiarid with dry summers and annual precipitation of 12 to 16 inches. The average annual temperature is about 42 to 45 degrees F. The frost-free season is about 80 to 100 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Arbone, Hondoho, and Ririe soils and the competing Arimo (T) soils. Arbone, Hondoho, and Ririe soils lack contrasting textures in the control section. In addition, Hondoho soils are loamy-skeletal and Ririe soils are coarse-silty. Arbone and Hondoho soils are on drainage slopes and terraces breaks. Arimo (T) soils are on the same landscape position as Downey soils, but where the deposits overlying sand and gravel are thicker. Ririe soils are on loess mantled terraces and foothills.
DRAINAGE AND PERMEABILITY: Well drained; slow and medium runoff; moderate permeability in the upper part and very rapid below.
USE AND VEGETATION: Mainly used for irrigated small grain, hay and pasture It is also used for rangeland. Potential natural vegetation is mainly Wyoming big sagebrush, tall green rabbitbrush, bluebunch wheatgrass and sandberg bluegrass. It has urban uses mainly in and around the cities of Downey, Virginia and, Arimo.
DISTRIBUTION AND EXTENT: Southeastern Idaho. This series is inextensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: Portneuf Area, Bannock County, Idaho, 1918.