LOCATION ROCKO MT
Established Series
Rev. GAR-JJU-RJS
06/2011
ROCKO SERIES
The Rocko series consists of very deep, well drained soils that formed in colluvium derived from mixed rock sources. These soils are on mountains. Slopes are 15 to 60 percent. Mean annual precipitation is about 22 inches, and the mean annual air temperature is about 36 degrees F.
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive Inceptic Haplocryalfs
TYPICAL PEDON: Rocko cobbly loam, forested (colors are for dry soil unless otherwise noted).
Oi--0 to 1 inch; slightly decomposed needles and twigs. (1 to 2 inches thick)
A--1 to 6 inches; very dark grayish brown (10YR 3/2) cobbly loam, black (10YR 2/1) moist; moderate medium granular structure; soft, very friable, slightly sticky and slightly plastic; many very fine and fine, and few medium roots; 5 percent gravel, 15 percent cobbles and 5 percent stones; neutral (pH 6.8); clear wavy boundary. (4 to 9 inches thick)
E--6 to 16 inches; light brownish gray (10YR 6/2) stony loam, dark grayish brown (10YR 4/2) moist; weak fine granular structure; soft, very friable, slightly sticky and slightly plastic; many very fine and fine, and few medium roots; 5 percent gravel, 15 percent cobbles and 10 percent stones; neutral (pH 6.8); clear wavy boundary. (0 to 15 inches thick)
Bt--16 to 29 inches; brown (10YR 5/3) very cobbly clay loam, dark grayish brown (10YR 4/2) moist; moderate medium subangular blocky structure; hard, firm, moderately sticky and moderately plastic; common very fine and fine, and few medium roots; common distinct clay films on faces of peds; 20 percent gravel, 20 percent cobbles and 5 percent stones; neutral (pH 7.2); clear wavy boundary. (5 to 13 inches thick)
BC--29 to 60 inches; pale brown (10YR 6/3) very cobbly loam, yellowish brown (10YR 5/4) moist; massive; slightly hard, friable, slightly sticky and slightly plastic; few very fine and fine roots; 20 percent gravel, 20 percent cobbles and 5 percent stones; slightly alkaline (pH 7.4).
TYPE LOCATION: Gallatin County, Montana; 2,500 feet east and 300 feet north of the southwest corner of section 30, T. 5N, R. 6E.
RANGE IN CHARACTERISTICS:
Mean annual soil temperature - 36 to 40 degrees F.
Mean summer soil temperature - 45 to 47 degrees F.
Thickness of A horizon - does not meet the mollic epipedon thickness requirements.
Note: Some pedons may have a C horizon.
A horizon
Hue: 10YR or 2.5Y; dry or moist
Value: 3 to 5 dry; 2 or 3 moist
Chroma: 1 to 3; dry or moist
Clay content: 18 to 27 percent
Rock fragments: 15 to 70 percent--5 to 30 percent gravel, 3 to 25 percent cobbles, 0 to 30 percent stones
Reaction: pH 6.1 to 7.3
E horizon
Hue: 10YR or 2.5Y; dry or moist
Value: 5 or 6 dry; 4 or 5 moist
Chroma: 1 or 2; dry or moist
Clay content: 18 to 27 percent
Rock fragments: 15 to 55 percent--5 to 25 percent gravel, 5 to 20 percent cobbles, 0 to 10 percent stones
Reaction: pH 6.1 to 7.3
Bt horizon
Hue: 10YR or 2.5Y; dry or moist
Value: 4 to 6 dry; 3 to 5 moist
Chroma: 2 to 4; dry or moist
Texture: clay loam, sandy clay loam or loam
Clay content: 25 to 35 percent
Rock fragments: 35 to 60 percent--15 to 30 percent gravel, 15 to 25 percent cobbles, 5 to 10 percent stones
Reaction: pH 6.1 to 7.8
BC horizon
Hue: 10YR or 2.5Y; dry or moist
Value: 5 or 6 dry; 4 or 5 moist
Chroma: 3 or 4; dry or moist
Texture: sandy loam, sandy clay loam or loam
Clay content: 18 to 27 percent
Rock fragments: 35 to 70 percent--15 to 35 percent gravel, 15 to 30 percent cobbles, 5 to 10 stones
Reaction: pH 6.6 to 7.8
C horizon (where present)
Hue: 10YR or 2.5Y; dry or moist
Value: 5 or 6 dry; 4 or 5 moist
Chroma: 3 or 4; dry or moist
Texture: sandy loam, sandy clay loam or loam
Clay content: 15 to 27 percent
Rock fragments: 35 to 70 percent--15 to 45 percent gravel, 15 to 30 percent cobbles, 0 to 10 stones
Reaction: pH 6.6 to 7.8
COMPETING SERIES:
Marosa (NM) - have a fragmental C horizon
GEOGRAPHIC SETTING:
Landform - mountains
Elevation - 5,400 to 7,800 feet
Slope - 15 to 60 percent
Parent material - colluvium derived from mixed rock sources
Climate - long, cold winters; cool, moist springs; short summers
Mean annual precipitation - 20 to 25 inches
Mean annual air temperature - 34 to 38 degrees F.
Frost-free period - 50 to 70 days
GEOGRAPHICALLY ASSOCIATED SOILS: None listed.
DRAINAGE AND PERMEABILITY: Well drained; moderately slow permeability.
USE AND VEGETATION: Rocko soils are used mainly for woodland and wildlife habitat. Potential native vegetation is mainly Douglas-fir with an understory of common snowberry, pinegrass and white spiraea.
DISTRIBUTION AND EXTENT: Rocko soils are of small extent in southwestern Montana. MLRA - 43B.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana.
SERIES ESTABLISHED: Gallatin County, Montana, 1997.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - from 0 to 6 inches (Oe, A horizon)
Albic horizon - from 6 to 16 inches (E horizon)
Argillic horizon - from 16 to 29 inches (Bt horizon)
Particle-size control section - from 16 to 29 inches (Bt horizon)
Rocko soils have a cryic temperature regime and an ustic moisture regime bordering on udic.
ADDITIONAL DATA: Soil interpretation record - MT1438.
Based on thickness of argillic horizon, the classification changed from Ustollic Haplocryalfs to Inceptic Haplocryalfs (01/2008)
National Cooperative Soil Survey
U.S.A.