LOCATION ORO FINO MTEstablished Series
TAXONOMIC CLASS: Fine-loamy, mixed, superactive Calcic Argicryolls
TYPICAL PEDON: Oro Fino gravelly loam, native grassland (colors are for dry soil unless otherwise noted).
A1--0 to 4 inches; dark grayish brown (10YR 4/2) gravelly loam, very dark brown (10YR 2/2) moist; weak medium platy structure parting to weak fine granular; soft, very friable, nonsticky and slightly plastic; many fine roots; many fine vesicular and tubular pores; 20 percent gravel; neutral (pH 6.8); clear smooth boundary. (2 to 6 inches thick)
A2--4 to 10 inches; dark grayish brown (10YR 4/2) gravelly loam, very dark brown (10YR 2/2) moist; moderate very coarse prismatic structure parting to weak medium subangular blocky; hard, friable, slightly sticky and slightly plastic; common fine roots; common fine irregular pores and few fine vesicular and tubular pores; 15 percent gravel; neutral (pH 6.8); clear smooth boundary. (3 to 10 inches thick)
Bt--10 to 22 inches; brown (10YR 5/3) gravelly sandy clay loam, brown (10YR 4/3) moist; strong very coarse prismatic structure parting to moderate fine subangular blocky; hard, firm, slightly sticky and moderately plastic; common fine roots; common fine irregular pores and few fine vesicular and tubular pores; common faint clay skins as bridges between sand grains; 15 percent gravel; neutral (pH 7.2); clear smooth boundary. (10 to 14 inches thick)
Bk1--22 to 34 inches; light gray (10YR 7/2) gravelly loam, light brownish gray (10YR 6/2) moist; massive; slightly hard, friable, nonsticky and nonplastic; common fine roots; 30 percent gravel; many soft masses of lime; violently effervescent; moderately alkaline (pH 7.9); abrupt wavy boundary. (12 to 15 inches thick)
Bk2--34 to 42 inches; brown (10YR 5/3) very gravelly sandy loam, brown (10YR 5/3) moist; massive; loose, nonsticky and nonplastic; few fine roots; common fine irregular pores; 40 percent gravel; common soft masses of lime; strongly effervescent; slightly alkaline (pH 7.6); clear wavy boundary. (7 to 10 inches thick)
Bk3--42 to 60 inches; brown (10YR 5/3) very gravelly loamy sand, brown (10YR 4/3) moist; single grain; loose, nonsticky and nonplastic; few fine roots in cracks; few fine irregular pores; 60 percent gravel; common soft masses of lime; strongly effervescent; slightly alkaline (pH 7.6).
TYPE LOCATION: Madison County, Montana; Sweetwater Divide; approximately 2,400 feet north and 1,000 feet west of the SE corner of sec. 13, T. 8 S., R. 7 W.
RANGE IN CHARACTERISTICS:
Soil temperature - 38 to 42 degrees F.
Moisture control section - between 4 and 12 inches.
Mollic epipedon thickness - 7 to 15 inches.
Depth to calcic horizon - 15 to 30 inches.
Some pedons have a BC horizon below 40 inches.
A horizons - Hue: 7.5YR or 10YR
Value: 3, 4, or 5 dry; 2 or 3 moist
Chroma: 2 or 3
Texture: loam, sandy loam, or coarse sandy loam
Clay content: 10 to 25 percent
Rock fragments: 10 to 30 percent gravel
Reaction: pH 6.6 to 7.8
Bt horizon - Hue: 7.5YR or 10YR
Value: 5 or 6 dry; 4 or 5 moist
Chroma: 3 or 4
Texture: sandy clay loam, clay loam, or loam
Clay content: 20 to 35 percent with more than 35 percent fine sand or coarser
Rock fragments: 15 to 35 percent gravel
Reaction: pH 6.6 to 7.8
Bk1 horizon - Hue: 7.5YR or 10YR
Value: 6, 7, or 8 dry; 5, 6, or 7 moist
Chroma: 2 to 6
Texture: loam, sandy loam, or coarse sandy loam
Clay content: 10 to 20 percent
Rock fragments: 15 to 35 percent gravel
Calcium Carbonate Equivalent: 10 to 15 percent
Reaction: pH 7.4 to 8.4
Bk2 horizon - Hue: 7.5YR or 10YR
Value: 5, 6, or 7 dry; 5 or 6 moist
Chroma: 2 to 6
Texture: loam, sandy loam, or coarse sandy loam
Clay content: 10 to 20 percent
Rock fragments: 15 to 45 percent gravel
Calcium Carbonate Equivalent: 5 to 10 percent
Reaction: pH 7.4 to 8.4
Bk3 horizon - Hue: 7.5YR or 10YR
Value: 5, 6, or 7 dry; 4, 5, or 6 moist
Chroma: 2 to 6
Texture: sand or loamy sand
Clay content: 5 to 10 percent
Rock fragments: 35 to 60 percent gravel
Calcium Carbonate Equivalent: 5 to 10 percent
Reaction: pH 7.4 to 8.4
COMPETING SERIES:
Accola (MT) - has an O horizon.
Michelson (MT) - has a buried argillic horizon below a depth of 40 inches.
Philipsburg (MT) - is not sandy-skeletal at depths of 40 to 60 inches.
GEOGRAPHIC SETTING:
Landform - hills, ridges, cuestas, pediments and mountains.
Elevation - 5,200 to 7,800 feet.
Slope - 2 to 45 percent.
Parent material - colluvium or slope alluvium derived from gneiss and schist.
Climate - long, cold winters; moist springs; short summers. Mean annual precipitation - 15 to 19 inches.
Mean annual temperature - 34 to 40 degrees F.
Frost-free period - 30 to 70 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Adel, Nieman, and Poin series. Adel soils have mollic epipedon more than 40 mm thick and lack argillic horizons. Nieman and Poin soils have bedrock at depths less than 20 inches.
DRAINAGE AND PERMEABILITY: Well drained; moderate permeability to about 42 inches and moderately rapid below.
USE AND VEGETATION: Oro Fino soils are used mainly for rangeland; some areas are used for irrigated and nonirrigated small grains and hay. Potential native vegetation is mainly Idaho fescue, bluebunch wheatgrass, lupine, and big sagebrush.
DISTRIBUTION AND EXTENT: Oro Fino soils are moderately extensive in the foothills of south western Montana. MLRA 43B and 44.
MLRA OFFICE RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Madison County, Montana, 1983.
REMARKS: Soil Interpretations Records: MT0405 and MT8066. Diagnostic horizons and features recognized in this pedon are: a mollic epipedon from the soil surface to 10 inches (A horizons); an argillic horizon which is the particle-size control section from 10 to 22 inches (Bt horizon); a calcic horizon from 22 to 60 inches (Bk horizons). Oro Fino soils have a cryic temperature regime and an ustic moisture regime.