LOCATION RIVRA                   MT

Established Series
Rev. JB-KTS-JCK
04/2021

RIVRA SERIES

The Rivra series consists of very deep, well drained soils that formed in alluvium. These soils are on flood plains and stream terraces. Slopes are 0 to 8 percent. Mean annual precipitation is about 330 mm and mean annual air temperature is about 6 degrees C.

TAXONOMIC CLASS: Sandy-skeletal, mixed, frigid Aridic Ustifluvents

TYPICAL PEDON: Rivra gravelly sandy loam, in native grass (colors are for dry soil unless otherwise noted).

A--0 to 20 cm, light brownish gray (2.5Y 6/2) gravelly sandy loam, dark grayish brown (2.5Y 4/2) moist; weak fine granular structure; soft, very friable, nonsticky and nonplastic; 20 percent gravel; finely disseminated calcium carbonate; slightly effervescent; slightly alkaline (pH 7.4); clear wavy boundary. (8 to 25 cm thick)

C1--20 to 81cm, grayish brown (2.5Y 5/2) very gravelly loamy coarse sand, dark grayish brown (2.5Y 4/2) moist; single grain; loose; nonsticky and nonplastic; common, decreasing with increasing depth to few, very fine and fine roots; 50 percent gravel and 10 percent cobbles and stones; finely disseminated calcium carbonate; strongly effervescent; moderately alkaline (pH 8.0).

C2--81 to 152 cm, grayish brown (2.5Y 5/2) extremely gravelly sand, with strata of loamy-sand; dark grayish brown (2.5Y 4/2) moist; single grain; loose; nonsticky and nonplastic; few roots; 55 percent gravel and 15 percent cobbles; finely disseminated calcium carbonate; strongly effervescent; moderately alkaline (pH 8.0).

TYPE LOCATION: Cascade County, Montana; 274 meters south and 219 meters east of the NW corner of sec. 10, T. 20 N., R. 3 W.

RANGE IN CHARACTERISTICS:
Mean annual soil temperature - 4.4 to 8.0 degrees C
Depth to a seasonally high water table - greater than 183 cm

A horizon
Hue: 10YR or 2.5Y; dry or moist
Value: 4 to 7 dry; 3 to 5 moist
Chroma: 1 to 3; dry or moist
Texture: loam, clay loam, sandy loam, fine sandy loam or loamy sand
Clay content: 0 to 35 percent
Rock fragments: 0 to 60 percent--0 to 50 percent gravel, 0 to 10 percent cobbles and stones
Reaction: pH 6.6 to 9.0

C1, C2 horizons
Hue: 10YR or 2.5Y; dry or moist
Value: 5 to 7 dry; 4 or 5 moist
Chroma: 2 to 4; dry or moist
Texture: sand and loamy coarse sand that consists of stratification of these and finer sands
Clay content: 0 to 5 percent
Rock fragments: 40 to 80 percent--35 to 70 percent gravel, 10 to 20 percent cobbles and stones
Reaction: pH 7.4 to 8.4

Some pedons have a thin buried A horizon above a depth of 100 cm.

COMPETING SERIES: There are no competing series.

GEOGRAPHIC SETTING:
Landform - flood plains and stream terraces
Elevation - 670 to 2,134 meters
Slope - 0 to 8 percent
Parent material - alluvium
Climate - long, cold winters and warm summers
Mean annual precipitation - 254 to 483 mm, most of which falls during the spring and early summer
Mean annual air temperature - 3.3 to 7.2 degrees C
Frost-free period - 70 to 135 days

GEOGRAPHICALLY ASSOCIATED SOILS:
These are the Havre and Ryell soils. The Havre soils are fine-loamy and the Ryell soils are coarse-loamy over sandy or sandy-skeletal. These soils occur on similar landforms as the Rivra soils.

DRAINAGE AND PERMEABILITY: Excessively drained; rapid or very rapid permeability.

USE AND VEGETATION: Rivra soils are used as range and pasture. The potential native vegetation is mainly bluebunch wheatgrass, western wheatgrass, needleandthread, prairie sandreed, forbs, and shrubs. There are a few dense stands of cottonwood trees in some areas.

DISTRIBUTION AND EXTENT: The Rivra soils are moderately extensive throughout Montana. MLRAs - 44B, 46, 52, 58A.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana.

SERIES ESTABLISHED: Broadwater County, Montana, 1971.

REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - from 0 to 20 cm (A horizon)
Particle-size control section - from 25 to 100 cm (C1, C2 horizons)

The Rivra soils have a frigid temperature regime and an ustic moisture regime bordering on aridic.

ADDITIONAL DATA: Soil interpretations records - MT0121, MT0717, MT0772, MT0793, MT0884, MT0885.

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National Cooperative Soil Survey
U.S.A.