LOCATION CROWNMOUNTAIN MT
Tentative Series
IRD: JJU-EMM
04/2015
CROWNMOUNTAIN SERIES
The Crownmountain series consists of very deep, somewhat poorly drained soils that formed in slide deposits and colluvium derived from mixed sedimentary rock sources. These soils occur on landslides, depressions, and mountain slopes. Slopes are 8 to 35 percent. Mean annual precipitation is about 560 mm, and mean annual air temperature is about 4 degrees C.
TAXONOMIC CLASS: Fine, mixed, superactive Oxyaquic Argicryolls
TYPICAL PEDON: Crownmountain silt loam, in forest on a 10 percent slope at an elevation of 1765 meters (colors are for dry soil unless otherwise noted).
Oi--0 to 5 cm; undecomposed and partially decomposed matted roots; abrupt smooth boundary. (3 to 10 cm thick)
A--5 to 31 cm; dark grayish brown (10YR 4/2) silt loam, black (10YR 2/1) moist; moderate medium granular structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine and few fine roots; many fine and very fine dendritic tubular pores; 5 percent gravel; neutral (pH 6.6); clear smooth boundary. (25 to 40 cm thick)
Bt1--31 to 60 cm; dark grayish brown (10YR 4/2) silty clay loam, very dark grayish brown (10YR 3/2) moist; strong coarse subangular blocky structure; moderately hard, friable, moderately sticky and moderately plastic; many fine and medium roots; common fine irregular pores; 45 percent distinct clay films on faces of peds; 5 percent gravel; slightly acid (pH 6.4); clear wavy boundary.
Bt2--60 to 76 cm; brown (10YR 4/3) silty clay loam, very dark grayish brown (10YR 3/2) moist; strong coarse subangular blocky structure; hard, firm, very sticky and very plastic; many very fine and fine roots; common fine irregular pores; 55 percent prominent clay films on faces of peds; 10 percent distinct medium irregular, strong brown (7.5YR 5/6) masses of iron accumulation; slightly acid (pH 6.4) clear wavy boundary. (combined thickness of Bt horizons - 35 to 55 cm thick)
BC--76 to 150 cm; brown (10YR 4/3) silty clay loam, dark grayish brown (10YR 4/2) moist; strong coarse subangular blocky structure; moderately hard, friable, moderately sticky and moderately plastic; few very fine and fine roots; few very fine irregular pores; 15 percent distinct medium irregular, strong brown (7.5YR 5/6) masses of iron accumulation; slightly acid (pH 6.4).
TYPE LOCATION: Lewis and Clark County, Montana; located 260 meters north and 410 meters west of the SE corner of sec. 14, T 19 N., R 9 W. Double Falls topographic quadrangle; UTM 12T, 371195e., 5250600n. NAD 83.
RANGE IN CHARACTERISTICS:
Mean annual soil temperature - 1 to 4 degrees C.
Mollic epipedon thickness - 40 to 70 cm
Depth to top of the argillic horizon - 30 to 45 cm
Depth to seasonal high water table: 60 to 100 cm during the spring for at least 20 consecutive days during normal years
Weighted average of clay content in particle size control section - greater than 35 percent.
A horizon
Value: 4 or 5 dry; 2 or 3 moist
Chroma: 1 to 3; dry or moist
Clay content: 18 to 27 percent
Rock fragments: 0 to 25 percent--0 to 15 percent gravel, 0 to 15 percent cobbles
Reaction: pH 6.2 to 6.8
Bt horizons
Value: 4 or 5 dry; 2 or 3 moist
Chroma: 2 or 3; dry or moist
Texture: clay loam or silty clay loam
Clay content: 30 to 40 percent
Rock fragments: 0 to 25 percent gravel
Reaction: pH 6.2 to 6.8
BC horizon
Value: 4 or 5 dry or moist
Chroma: 2, 3 or 4; dry or moist
Texture: clay loam or silty clay loam
Clay content: 27 to 35 percent
Rock fragments: 0 to 25 percent gravel
Reaction: pH 6.2 to 6.8
COMPETING SERIES:
Beaverslide (MT) - have secondary calcium carbonate accumulation
GEOGRAPHIC SETTING:
Landform - landslides, depressions, and mountain slopes
Elevation - 1700 to 2135 meters
Slope - 8 to 35 percent
Parent material - slide deposits and colluvium from mixed sedimentary sources.
Climate - long, cold winters; cool, moist springs; short, warm summers
Mean annual precipitation - 480 to 610 mm.
Mean annual air temperature - 1 to 4 degrees C.
Frost-free period - 50 to 70 days
GEOGRAPHICALLY ASSOCIATED SOILS: None listed
DRAINAGE AND PERMEABILITY: somewhat poorly drained, moderately slow permeability.
USE AND VEGETATION: Crownmountain soils are used for wildlife and recreation. The vegetation is mainly quaking aspen mixed with Douglas-fir, birchleaf spirea, snowberry species, sweet cicely, Oregon grape, northern bedstraw and western meadowrue.
DISTRIBUTION AND EXTENT: Crownmountain soils are of limited extent in central Montana. MLRA 43B.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana.
SERIES PROPOSED: Lewis and Clark County, Montana, 2014.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - from 5 to 72 cm (A, Bt1 and Bt2 horizons);
Argillic horizon - from 31 to 72 cm (Bt1 and Bt2 horizons);
Horizons with iron accumulations - from 60 to 150 cm (Bt1, Bt2 and BC horizons);
Particle-size control section - from 31 to 72 cm (Bt1 and Bt2 horizons).
Crownmountain soils have a cryic temperature regime, an ustic moisture regime and an oxyaquic moisture subclass.
Taxonomic version: Eleventh Edition, 2010.
National Cooperative Soil Survey
U.S.A.