LOCATION TRAPPS MT
Established Series
Rev. BDD/JAL/KLS
07/2022
TRAPPS SERIES
The Trapps series consists of very deep, well drained soils that formed in colluvium or alluvium derived from limestone or argillite and in glacial till. These soils are on mountains and glacial moraines. Slopes are 4 to 80 percent. Mean annual precipitation is about 520 mm and mean annual air temperature is about 6 degrees C.
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, frigid Typic Haplustalfs
TYPICAL PEDON: Trapps gravelly loam, forested (colors are for dry soil unless otherwise noted).
Oi--0 to 5 cm; undecomposed and slightly decomposed forest litter.
E--5 to 30 cm; light gray (10YR 7/2) gravelly loam, grayish brown (10YR 5/2) moist; moderate fine and medium granular structure; slightly hard, very friable, nonsticky and nonplastic; many very fine, fine, medium, and coarse roots; many very fine pores; 25 percent pebbles; neutral (pH 6.8); clear wavy boundary. (5 to 38 cm thick)
Bt--30 to 66 cm; yellowish brown (10YR 5/4) very gravelly clay loam, dark yellowish brown (10YR 4/4) moist; moderate fine and medium subangular blocky structure; hard, friable, moderately sticky and moderately plastic; many very fine, fine, medium, and coarse roots; many very fine pores; common distinct clay films on faces of peds; 40 percent pebbles; slightly alkaline (pH 7.8); clear wavy boundary. (25 to 50 cm thick)
Bk1--66 to 94 cm; very pale brown (10YR 7/3) very gravelly loam, yellowish brown (10YR 5/4) moist; weak medium and coarse subangular blocky structure; slightly hard, very friable, slightly sticky and slightly plastic; few very fine, fine, medium, and coarse roots; common very fine pores; lime coatings on underside of pebbles; 50 percent pebbles; disseminated lime; strongly effervescent; moderately alkaline (pH 8.4); gradual wavy boundary. (13 to 38 cm thick)
Bk2--94 to 158 cm; very pale brown (10YR 7/3) extremely gravelly loam, light yellowish brown (10YR 6/4) moist; massive; soft, very friable, nonsticky, and nonplastic; few very fine, fine, medium, and coarse roots; common very fine pores; lime coatings on underside of coarse fragments; 50 percent pebbles, 20 percent cobbles; disseminated lime; violently effervescent; moderately alkaline (pH 8.4).
TYPE LOCATION: Missoula County, Montana; about 90 meters north and 245 meters east of the W 1/4 corner of sec. 21, T. 11 N., R. 20 W.
RANGE IN CHARACTERISTICS:
Mean annual soil temperature--4 to 8 degrees C
Moisture control section--10 to 30 cm
Depth to Bk horizon--40 to 90 cm
Some pedons have a thin A horizon, less than 10 cm thick, with mollic colors.
E horizon
Value--6 or 7 dry; 5 or 6 moist
Chroma--2 through 4
Clay content--10 to 27 percent
Rock fragment content--15 to 35 percent; 0 to 20 percent cobbles, flagstones, and stones; 15 to 25 percent pebbles or channers
Reaction--pH 5.6 to 7.3
Bt horizon
Hue--7.5YR, 10YR, or 2.5Y
Value--5 through 7 dry; 3 through 5 moist
Chroma--2, 3, 4, or 6
Clay content--27 to 35 percent
Rock fragment content--35 to 60 percent; 0 to 10 percent cobbles or flagstones; 35 to 50 percent gravel or channers
Reaction--pH 6.6 to 8.4
Bk1 horizon
Hue--7.5YR, 10YR, or 2.5Y
Value--6 through 8 dry; 5 or 6 moist
Chroma--2, 3, 4, 6, or 8
Texture--loam or sandy loam
Clay content--10 to 15 percent
Rock fragment content--35 to 60 percent; 0 to 20 percent cobbles, flagstones, or stones; 35 to 40 percent pebbles or channers
Calcium carbonate equivalent--15 to 40 percent
Reaction--pH 7.9 to 8.4
Bk2 horizon
Hue--7.5YR, 10YR, or 2.5Y
Value--6 through 8 dry; 5 or 6 moist
Chroma--2, 3, 4, 6, or 8
Texture--loam or sandy loam
Clay content--10 to 15 percent
Rock fragment content--45 to 85 percent; 10 to 30 percent cobbles, flagstones, or stones; 50 to 55 percent pebbles or channers
Calcium carbonate equivalent--10 to 35 percent
Reaction--pH 7.9 to 8.4
COMPETING SERIES:
Abreu (NM) - has a lithic contact at 100 to 150 cm; does not have horizons of secondary carbonate accumulation
Amcec (NM) - coarse fragments consist of cinders and basalt; has hues of 2.5YR or 5YR in the argillic horizon and below.
Colomex (NM) - does not have horizons of secondary carbonate accumulation; has a lithologic discontinuity.
Laventana (NM) - does not have horizons of secondary carbonate accumulation.
Macmeal (MT) - has a Bt horizon that is 50 to 115 cm thick.
Mocmont (MT) - has a mixed E/Bt horizon; does not have a horizon of secondary calcium carbonate accumulation.
Sheek (CO) - does not have horizon of secondary carbonate accumulation.
Skyview (MT) - has a lithic contact at 58 to 100 cm; does not have horizons of secondary carbonate accumulation.
Sonsela (NM) - does not have horizons of secondary carbonate accumulation.
Vision (MT) - does not have horizons of secondary carbonate accumulation.
Wahatoya (CO) - has a lithic contact at 50 to 100 cm; does not have horizons of secondary carbonate accumulation.
Ymark (MT) - has a lithic contact at 100 to 150 cm; does not have horizons of secondary carbonate accumulation.
Yourame (MT) - has a Bt horizon that is 50 to 100 cm thick; calcareous at a depth of 90 to 130 cm.
Yreka (MT) - has a mixed E/Bt horizon; does not have a horizon of secondary calcium carbonate accumulation.
GEOGRAPHIC SETTING:
Landform--mountains; glacial moraines
Elevation--1025 to 1975 meters
Slope--4 to 80 percent
Parent material--colluvium or alluvium derived from limestone and argillite rock, and in glacial till
Climate--long, cold winters; moist springs; warm summers
Mean annual precipitation--380 to 640 mm
Mean annual temperature--3 to 7 degrees C
Frost-free period--70 to 105 days
GEOGRAPHICALLY ASSOCIATED SOILS: None listed
DRAINAGE AND PERMEABILITY: Well drained; moderately slow permeability to a depth of 60 cm and moderate permeability below.
USE AND VEGETATION: Trapps soils are used mainly for timber production, watersheds, and for wildlife habitat. Potential native vegetation is mainly Douglas fir, western larch, and ponderosa pine with an understory of common snowberry, mallow ninebark, elk sedge, pinegrass, dwarf huckleberry, and blue huckleberry.
DISTRIBUTION AND EXTENT: Trapps soils are moderately extensive in western Montana; MLRAs 43A, 43B and 46
SOIL SURVEY REGIONAL OFFICE (SSRO) RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Missoula County, Montana, 1985
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Albic horizon and ochric epipedon--5 to 30 cm (E horizon)
Argillic horizon--30 to 66 cm (Bt horizon)
Calcic horizon--66 to 158 cm (Bk1, Bk2 horizons)
Particle-size control section--30 to 66 cm (Bt horizon)
Trapps soils have a frigid temperature regime and an ustic soil moisture regime with a typic subclass.
Converted to metric, updated formatting, and O horizons were updated to start at zero. 7/2022
Soil interpretation record--MT0539, MT1145, MT1178, MT9041
National Cooperative Soil Survey
U.S.A.