LOCATION DOWNATA IDEstablished Series
TAXONOMIC CLASS: Fine-silty, mixed, superactive, calcareous, frigid Cumulic Endoaquolls
TYPICAL PEDON: Downata silt loam - on a nearly level flood plain under sedge and grass vegetation at 4,697 feet elevation. (Colors are for dry soil unless otherwise noted.)
Oi--0 to 1 inch; slightly decomposed grass and moss. (0 to 2 inches thick)
Ag1--1 to 3 inches; grayish brown (2.5Y 5/2) silt loam, very dark grayish brown (2.5Y 3/2) moist; weak very fine granular structure; soft, very friable, slightly sticky and slightly plastic; many very fine, fine, and medium roots; many very fine irregular pores; strongly effervescent; slightly alkaline (pH 7.7); abrupt wavy boundary. (2 to 6 inches thick)
Ag2--3 to 7 inches; grayish brown (2.5Y 5/2) silt loam, very dark grayish brown (2.5Y 3/2) moist; common fine prominent dark yellowish brown (10YR 3/6) mottles; weak fine granular structure; soft, very friable, slightly sticky and slightly plastic; many very fine, fine, and medium roots; many very fine irregular pores; strongly effervescent; slightly alkaline (pH 7.6); abrupt wavy boundary. (2 to 6 inches thick)
Bg--7 to 15 inches; grayish brown (2.5Y 5/2) silt loam, very dark grayish brown (2.5Y 3/2) moist; many fine prominent dark yellowish brown (10YR 3/6) redox concentrations; weak coarse subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine, fine, and medium roots; many very fine irregular pores and few fine tubular pores; strongly effervescent; slightly alkaline (pH 7.6); abrupt smooth boundary. (6 to 16 inches thick)
2Agb--15 to 21 inches; dark gray (5Y 4/1) silty clay loam, black (5Y 2.5/1) moist; weak coarse subangular blocky structure; hard, friable, moderately sticky and moderately plastic; many very fine roots, and common fine and medium roots; common very fine tubular pores; strongly effervescent; slightly alkaline (pH 7.7); clear smooth boundary. (5 to 8 inches thick)
2Bgb1--21 to 31 inches; gray (5Y 5/1) silty clay loam, very dark gray (5Y 3/1) moist; weak coarse subangular blocky structure; hard, friable, moderately sticky and moderately plastic; few very fine and fine roots; many very fine tubular pores; violently effervescent; moderately alkaline (pH 7.9); abrupt smooth boundary. (8 to 16 inches thick)
2Bgb2--31 to 41 inches; light brownish gray (2.5Y 6/2) silty clay loam, dark grayish brown (2.5Y 4/2) moist; weak coarse subangular blocky structure; very hard, friable, slightly sticky and slightly plastic; few very fine and fine roots; common very fine tubular pores; violently effervescent; moderately alkaline (pH 8.0); abrupt smooth boundary. (5 to 15 inches thick)
2Bgb3--41 to 61 inches; light gray (N 7/) silt loam, gray (2.5Y 5/1) moist; weak coarse subangular blocky structure; very hard, friable, slightly sticky and slightly plastic; few very fine and fine roots; common very fine tubular pores; violently effervescent; moderately alkaline (pH 7.9).
TYPE LOCATION: Bannock County, Idaho; about 3.25 miles west of Downey; 1,400 feet west and 20 feet north of the southeast corner of sec. 25, T. 11 S., R. 36 E.
RANGE IN CHARACTERISTICS:
Mollic epipedon thickness - 24 to 40 inches
Particle-size control section - 28 to 34 percent clay
Depth to high water table - +12 to 20 inches (January to June)
Average annual soil temperature - 42 to 46 degrees F
Ag horizon
Hue - 10YR, 2.5Y, or N
Chroma, moist or dry - 2 or 3
Redox concentrations, contrast - distinct or prominent
Hue - 10YR or 2.5Y
Value, dry - 4 or 5
Value, moist - 2 through 6
Chroma, moist - 3 through 8
Reaction - slightly alkaline or moderately alkaline
Bg horizon
Hue - 2.5Y or N
Chroma, moist or dry - 2 or 3
Redox concentrations, contrast - distinct or prominent
Hue - 10YR or 2.5Y
Value, dry - 2 through 5
Value, moist - 2 through 6
Chroma, moist - 1 through 8
Reaction - slightly alkaline or moderately alkaline
2Agb horizon
Hue - 2.5Y, N, or 5Y
Value, moist - 2, 2.5, or 3
Value, dry - 3 through 5
Chroma, moist or dry - 1 or 2
Texture - silt loam or silty clay loam
Reaction - slightly alkaline or moderately alkaline
2Bg horizon
Hue - 2.5Y, N, or 5Y
Value, moist - 3 through 5
Value, dry - 5 through 7
Chroma, moist or dry - 0 through 2
Texture - silt loam or silty clay loam - also, thin lenses of fine
sandy loam, loamy fine sand, fine sand or loam are in some pedons.
Reaction - slightly alkaline or moderately alkaline
Buried organic layers of sapric material ranging from 1 to 6 inches in thickness are present in some pedons.
COMPETING SERIES: These are the Bigstone, Bloomington, Halleck, Homefield, Inkom, Lamoure, Opie, Playmoor, and Rauville series. Bigstone soils and Bloomington soils are saturated in the moisture control section for more than 20 days following the summer solstice in most years. Halleck soils lack buried horizons. Homefield soils have a calcic horizon and a 2C horizon at 40-60 inches. Inkom soils average 18-27 percent clay in the particle size control section. Lamoure soils are somewhat poorly drained and have a mollic epipedon with chroma of 1 or less. Opie soils have a calcic horizon and a 2C horizon with 10-30 percent gravel. Playmoor soils have salt accumulations (4 to 16 mmhos/cm), including gypsum, in the upper 20 inches. Rauville soils are saturated in the soil moisture control section during the 120 days following the summer solstice, and have chroma of 1 or less to a depth greater than 40 inches.
GEOGRAPHIC SETTING: Downata soils are on flood plains and low stream terraces. Slopes range from 0 to 1 percent. They formed in silty alluvium derived from mixed sources. The average annual precipitation ranges from 12 to 16 inches, and the average annual temperature ranges from 41 to 45 degrees F. The frost-free season is about 80 to 100 days. Elevation ranges from 4,500 to 4,800 feet.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Bear Lake, Tendoy (T), and the competing Inkom soils. Bear Lake soils lack buried horizons and have a calcic horizon. Tendoy soils are organic and are on slightly lower positions on flood plains. Inkom soils are on slightly higher positions on flood plains and terraces and are better drained. Bear Lake soils are on nearly the same landscape position but the micro-relief is generally slightly convex.
DRAINAGE AND PERMEABILITY: Poorly and very poorly drained; runoff is very slow or ponded; permeability is moderately slow. These soils are frequently flooded and/or ponded from January through June for brief periods of 3 to 5 days.
USE AND VEGETATION: Used mainly for meadow hay and pasture. Most Downata soils have been drained so that hay can be harvested. Potential natural vegetation is grasses, sedges, and rushes.
DISTRIBUTION AND EXTENT: Southeastern, Idaho. This series is inextensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Bannock County, Idaho, 1983.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - the zone from 1 to 31 inches (Ag1, Ag2, Bg, 2Agb and 2Bgb1 horizons)
Aquic moisture regime