LOCATION MEGONOT MTEstablished Series
TAXONOMIC CLASS: Fine, smectitic, frigid Torrertic Haplustepts
TYPICAL PEDON: Megonot silty clay loam, in non-irrigated cropland. (Colors are for dry soil unless otherwise noted)
Ap--0 to 5 inches; grayish brown (2.5Y 5/2) silty clay loam, dark grayish brown (2.5Y 4/2) moist; moderate medium granular structure; hard, friable, sticky and plastic; many fine roots; many fine vesicular pores; slightly effervescent; neutral (pH 7.2); clear smooth boundary. (3 to 10 inches thick)
Bw--5 to 12 inches; grayish brown (2.5Y 5/2) silty clay loam, dark grayish brown (2.5Y 4/2) moist; weak medium prismatic structure parting to moderate medium and fine subangular blocky; hard, friable, sticky and plastic; common fine and very fine roots; common fine and very fine discontinuous tubular pores; disseminated lime; slightly effervescent; slightly alkaline (pH 7.6); clear smooth boundary. (7 to 20 inches thick)
Bk--12 to 21 inches; grayish brown (2.5Y 5/2) silty clay, dark grayish brown (2.5Y 4/2) moist; moderate medium prismatic structure parting to moderate medium and fine subangular blocky; very hard, firm, sticky and very plastic; common fine and very fine roots; common very fine discontinuous tubular pores; 10 percent soft weathered shale fragments; few medium masses of segregated lime; strongly effervescent; moderately alkaline (pH 8.2); clear wavy boundary. (6 to 20 inches thick)
By--21 to 29 inches; grayish brown (2.5Y 5/2) silty clay, dark grayish brown (2.5Y 4/2) moist; massive or thin platy structure as a result of in situ weathering of shale; hard, firm, sticky and plastic; common fine and very fine roots in cracks and between plates; common fine threads and seams of gypsum; 25 percent soft shale fragments, 10 percent hard shale fragments; disseminated lime; slightly effervescent; moderately alkaline (pH 8.0); gradual wavy boundary. (0 to 12 inches thick)
2Cr--29 to 60 inches; mixed dark gray (5Y 4/1) and olive gray (5Y 4/2) semi-consolidated shale; hard and firm; neutral (pH 6.8).
TYPE LOCATION: Teton County, Montana; 1,200 feet east and 1,500 feet north of the SW corner of sec. 29, T. 23 N., R. 2 W.
RANGE IN CHARACTERISTICS:
Soil temperature - 41 to 47 degrees F.
Moisture control section - between 4 and 12 inches; dry in all parts between four-tenths and five-tenths of the cumulative days per year when the soil temperature at 20 inches is 41 degrees F or above.
Rock fragments - 0 to 15 percent hard shale fragments.
Depth to bedrock - 20 to 40 inches.
Depth to secondary lime - 10 to 27 inches.
A Bky horizon is allowed.
Depth to paralithic contact - 20 to 40 inches.
Ap horizon - Hue: 10YR or 2.5Y
Value: 5 or 6 dry, 4 or 5 moist
Chroma: 2 or 3
Texture: silty clay loam, clay loam, or silty clay
Clay content: 27 to 45 percent
Coarse fragments: 0 to 15 percent pebbles
Reaction: pH 6.6 to 7.8
Bw horizons - Hue: 10YR or 2.5Y
Value: 5 or 6 dry, 4 or 5 moist
Chroma: 2 or 3
Texture: silty clay loam, clay loam, clay or silty clay
Clay content: 35 to 50 percent
Coarse fragments: 0 to 15 percent hard pebbles, 0 to 15 percent soft pebbles
Calcium carbonate equivalent: 1 to 12 percent
Reaction: pH 7.4 to 8.4
Bk horizon - Hue: 10YR, 2.5Y or 5Y
Value: 5 or 6 dry; 4 or 5 moist
Chroma: 2 or 3
Texture: silty clay loam, clay loam, clay or silty clay
Clay content: 35 to 50 percent
Coarse fragments: 0 to 15 percent hard pebbles, 0 to 15 percent soft pebbles
Calcium carbonate equivalent: 5 to 15 percent
Reaction: pH 7.4 to 8.4
By horizon - Hue: 10YR, 2.5Y or 5Y
Value: 4, 5, or 6 dry; 3, 4 or 5 moist
Chroma: 2 or 3
Texture: silty clay loam, clay loam, clay or silty clay
Clay content: 35 to 45 percent
Coarse fragments: 10 to 50 percent soft shale; 5 to 30 percent hard shale fragments
Gypsum: 1 to 5 percent
Reaction: pH 6.6 to 8.4
2Cr horizon - semi-consolidated shale or mudstone
Reaction: pH 5.6 to 7.8
COMPETING SERIES:
Alzada (MT) - does not have a paralithic contact at depths of 20 to 40 inches.
Brunelda (MT) - has a gypsic horizon; does not have a paralithic contact above a depth of 60 inches.
Kobase (MT) - does not have a paralithic contact at depths of 20 to 40 inches.
Nunemaker (MT) - does not have a paralithic contact above a depth of 40 inches.
Teigen (MT) - does not have a paralithic contact above a depth of 40 inches.
Zatoville (MT) - has a gypsic horizon; has horizons of other salt accumulations.
GEOGRAPHIC SETTING:
Landform - dissected alluvial fans; strath terraces; sedimentary plains; lake plains; hills; escarpments; ridges.
Elevation - 2,200 to 5,200 feet.
Slope- 0 to 60 percent.
Parent material - residuum from semi-consolidated shale, siltstone or mudstone, or in alluvium over the semi-consolidated shale, siltstone or mudstone.
Climate - long, cold winters; moist springs; hot, dry summers.
Mean annual precipitation - 10 to 16 inches.
Mean annual air temperature - 39 to 45 degrees F.
Frost-free season - 95 to 135 days.
GEOGRAPHICALLY ASSOCIATED SOILS:
DRAINAGE AND PERMEABILITY: Well drained; slow permeability.
USE AND VEGETATION: Megonot soils are used as rangeland and non-irrigated cropland. Potential native vegetation is mainly bluebunch wheatgrass, green needlegrass, western wheatgrass, needleandthread, winterfat, and skunkbush sumac.
DISTRIBUTION AND EXTENT: Megonot soils are of moderate extent in north central Montana and in Colorado.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: St. Paul, Minnesota
SERIES ESTABLISHED: Choteau-Conrad Area, Montana, 1990.
REMARKS: Soil interpretations record: MT0684.
Diagnostic horizons and features recognized in this pedon are: ochric epipedon - from the soil surface to 5 inches (Ap horizon); cambic horizon - from 5 to 12 inches (Bw horizon); horizon of secondary carbonate accumulation - from 12 to 21 inches (Bk horizon); horizon of gypsum accumulation - from 21 to 29 inches (By horizon); paralithic contact of semi-consolidated shale - at a depth of 29 inches (Cr horizon); particle-size control section - from 10 to 29 inches (Bw, Bk, By horizons). Megonot soils have a frigid temperature regime and an ustic moisture regime that borders on aridic.