LOCATION ROCKISLAND MT
Established Series
REV. KTS-JJU-RJS
01/2012
ROCKISLAND SERIES
The Rockisland series consists of very deep well drained soils that formed in alluvium, slope alluvium or colluvium derived from mixed sources. These soils occur on stream terraces, alluvial fans, fan remnants, escarpments, hills and mountain slopes. Slopes are 8 to 60 percent. Mean annual precipitation is about 400 mm and mean annual temperature is about 3 degrees C.
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive Calcic Haplocryolls
TYPICAL PEDON: Rockisland loam, in rangeland on a 40 percent slope at an elevation of 2262 meters (colors are for dry soil unless otherwise noted).
A--0 to 11 cm; very dark grayish brown (10YR 3/2) loam, very dark brown (10YR 2/2) moist; weak fine and medium granular structure; slightly hard, very friable, slightly sticky and nonplastic; many very fine, fine and medium roots; many very fine irregular pores; 10 percent gravel; neutral (pH 6.8); clear smooth boundary. (8 to 24 cm thick)
Bw--11 to 26 cm; dark grayish brown (10YR 4/2) gravelly loam, very dark grayish brown (10YR 3/2) moist; moderate medium subangular blocky structure; slightly hard, very friable, slightly sticky and slightly plastic; many very fine, fine and medium roots; many very fine irregular pores; 15 percent gravel; neutral (pH 7.2); clear smooth boundary. (0 to 35 cm thick)
Bk1--26 to 61 cm; pale brown (10YR 6/3) very gravelly loam, brown (10YR 5/3) moist; weak medium subangular blocky structure; slightly hard, very friable, slightly sticky and slightly plastic; many very fine and fine, and few medium roots; many very fine tubular and irregular pores; 40 percent gravel and 5 percent cobbles; finely disseminated calcium carbonate, 5 percent medium, distinct, irregular, soft masses of calcium carbonate, and 90 percent distinct calcium carbonate coats on bottom of rock fragments; violently effervescent; moderately alkaline (pH 8.2); clear smooth boundary. (10 to 50 cm thick)
Bk2--61 to 152 cm; pale brown (10YR 6/3) very gravelly loam, brown (10YR 5/3) moist; weak fine subangular blocky structure; soft, very friable, slightly sticky and nonplastic; few very fine and fine roots; many very fine irregular pores; 45 percent gravel and 5 percent cobbles; finely disseminated calcium carbonate, 10 percent medium, distinct, irregular, soft masses of calcium carbonate, and 65 percent distinct calcium carbonate coats on rock fragments; violently effervescent; moderately alkaline (pH 8.2); gradual wavy boundary.
TYPE LOCATION: Beaverhead County, Montana; located about 2,500 feet west and 2,500 feet north of the southeast corner of sec. 31, T. 11S, R. 8W; Rock Island Ranch topographic quadrangle; UTM 12T, 371639e, 4965758n, NAD 83.
RANGE IN CHARACTERISTICS:
Mean annual soil temperature - 2 to 5 degrees C.
Mollic epipedon thickness - 18 to 40 cm
Depth to calcic horizon - 20 to 50 cm
Particle-size control section (weighted average) - 18 to 27 percent clay
Note: Some pedons may have an A2 and/or BCk horizon.
A horizon
Value: 3 to 5 dry; 2 or 3 moist
Chroma: 2 or 3; dry or moist
Clay content: 15 to 27 percent
Rock fragments: 5 to 35 percent--5 to 30 percent gravel, 0 to 10 percent cobbles
Reaction: pH 6.8 to 7.4
Bw horizon
Value: 3 to 5 dry; 2 or 3 moist
Chroma: 2 or 3; dry or moist
Clay content: 15 to 27 percent
Rock fragments: 5 to 35 percent--5 to 30 percent gravel, 0 to 10 percent cobbles
Reaction: pH 6.8 to 7.4
Bk1, Bk2 horizons
Value: 5 or 6 dry; 4 or 5 moist
Chroma: 2 or 3; dry or moist
Texture: loam, sandy loam or sandy clay loam
Clay content: 15 to 27 percent
Rock fragments: 35 to 75 percent--25 to 60 percent gravel, 0 to 25 percent cobbles and stones
Calcium carbonate equivalent: 15 to 35 percent
Reaction: pH 7.9 to 8.4
COMPETING SERIES:
Farlow (WY) - are deep to a lithic contact
Mcninch (MT) - average less than 18 percent clay in the particle-size control section
Silvercliff (CO) - average less than 18 percent clay in the particle-size control section
Windicreek (ID) - average less than 18 percent clay in the particle-size control section
GEOGRAPHIC SETTING:
Landform - stream terraces, alluvial fans, fan remnants, escarpments, hills and mountain slopes
Elevation - 1830 to 2600 meters
Slope - 2 to 60 percent
Parent material - alluvium, slope alluvium or colluvium derived from mixed sources
Climate - long, cold winters; moist springs; warm summers
Mean annual precipitation - 380 to 560 mm
Mean annual air temperature - 1 to 4 degrees F.
Frost-free period - 30 to 70 days
GEOGRAPHICALLY ASSOCIATED SOILS: None listed.
DRAINAGE AND PERMEABILITY: Well drained; moderate permeability.
USE AND VEGETATION: Rockisland soils are used mainly for rangeland. The vegetation is mainly bluebunch wheatgrass, Idaho fescue, POA (species), prairie junegrass, mountain big sagebrush, threetip sagebrush, rubber rabbitbrush and other forbs.
DISTRIBUTION AND EXTENT: Rockisland soils are of small extent in southwestern Montana. MLRA - 43B, 44B.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana.
SERIES ESTABLISHED: Horse Prairie-South Valley Area - Part of Beaverhead County, Montana, 2011; proposed in Beaverhead County, Montana, 2008.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - from 0 to 26 cm (A, Bw horizons)
Calcic horizon - from 26 to 152 cm (Bk1, Bk2 horizons)
Particle-size control section - from 25 to 100 cm (part of Bw, Bk1, part of Bk2 horizons).
Rockisland soils have a cryic temperature regime and an ustic moisture regime.
National Cooperative Soil Survey
U.S.A.