LOCATION TROPAL                  MT

Established Series
Rev. LCB-JJU-RJS
09/2011

TROPAL SERIES

The Tropal series consists of shallow, well drained soils that formed in colluvium over residuum derived from limestone. These soils are on hills, canyon walls, ridges, mountains and structural bench. Slopes are 4 to 70 percent. Mean annual precipitation is about 17 inches, and mean annual air temperature is about 38 degrees F.

TAXONOMIC CLASS: Loamy-skeletal, carbonatic Lithic Calcicryepts

TYPICAL PEDON: Tropal very gravelly loam, bouldery, forested (colors are for dry soil unless otherwise noted).

Oi--0 to 0.5 inches; partially decomposed needles, twigs, and leaves.

A--0.5 to 4 inches; brown (10YR 5/3) very gravelly loam, dark grayish brown (10YR 4/2) moist; moderate medium granular structure, slightly hard, very friable, nonsticky and nonplastic; many fine roots; common very fine and fine pores; 40 percent gravel and 5 percent cobbles; continuous distinct calcium carbonate coatings on underside of fragments; violently effervescent; moderately alkaline (pH 8.2); abrupt smooth boundary. (3 to 6 inches thick)

Bk--4 to 16 inches; light gray (10YR 7/2) extremely gravelly loam, grayish brown (10YR 5/2) moist; moderate medium subangular blocky structure; slightly hard, very friable, slightly sticky and slightly plastic; many fine roots; common very fine and fine pores; 50 percent gravel and 10 percent cobbles; continuous prominent calcium carbonate casts on fragments, and finely disseminated calcium carbonate; violently effervescent; moderately alkaline (pH 8.4); gradual wavy boundary. (7 to 15 inches thick)

R--16 inches; light gray (10YR 7/1) hard limestone.

TYPE LOCATION: Jefferson County, Montana; 700 feet west and 1,800 feet north of the southeast corner of sec. 3, T. 5N, R. 2W.

RANGE IN CHARACTERISTICS:
Soil temperature - 38 to 42 degrees F.
Depth to a lithic contact - 10 to 20 inches (mainly 12 to 20 inches)
Particle-size control section (weighted average) - greater than 35 percent rock fragments

Note: Some pedons may have a thin Bw horizon.

A horizon
Hue: 10YR or 2.5Y; dry or moist
Value: 4 or 5 dry; 3 or 4 moist
Chroma: 2 or 3; dry or moist
Clay content: 15 to 25 percent
Rock fragments: 15 to 60 percent--15 to 45 percent gravel, 0 to 15 percent stones and cobbles
Calcium carbonate equivalent: 0 to 25 percent
Reaction: pH 7.4 to 8.4

Bk horizon
Hue: 10YR or 2.5Y; dry or moist
Value: 5 to 8 dry; 5 to 7 moist
Chroma: 2 or 3; dry or moist
Clay content: 10 to 25 percent
Rock fragments: 15 to 80 percent--15 to 60 percent gravel, 5 to 25 percent cobbles and stones
Calcium carbonate equivalent: 40 to 60 percent
Reaction: pH 7.4 to 9.0

COMPETING SERIES:
Henneberry (MT) - have hues redder than 10YR

GEOGRAPHIC SETTING:
Landform - hills, canyon walls, ridges, mountains and structural bench
Elevation - 5,000 to 9,000 feet
Slope - 4 to 70 percent
Parent material - colluvium over residuum derived from limestone
Climate - long, cold winters; cool, moist springs; cool summers
Mean annual precipitation - 14 to 30 inches
Mean annual temperature - 36 to 40 degrees F.
Frost-free period - 30 to 70 days

GEOGRAPHICALLY ASSOCIATED SOILS: None listed.

DRAINAGE AND PERMEABILITY: Well drained; moderate permeability.

USE AND VEGETATION: Tropal soils are used for woodland and rangeland. Potential native vegetation is mainly Douglas-fir, lodgepole pine, limber pine, common juniper, Idaho fescue, bluebunch wheatgrass, kinnikinnick, Oregon grape, and arrowleaf balsamroot. In rangeland the potential vegetation is bluebunch wheatgrass, Idaho fescue, and big sagebrush.

DISTRIBUTION AND EXTENT: Tropal soils are of moderate extent in western and central Montana. MLRA - 43B, 44B.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana.

SERIES ESTABLISHED: Broadwater County, Montana, 1971. Type location moved to Jefferson County, Montana, 1993.

REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - from 0 to 4 inches (Oi, A horizons)
Calcic horizon - from 4 to 16 inches (Bk horizon)
Lithic contact - at 16 inches (R horizon)
Particle-size control section - from 10 to 16 inches (part of Bk horizon)

Tropal soils have a cryic temperature regime and an ustic moisture regime.

ADDITIONAL DATA: Soil interpretations records - MT0517, MT8136.

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National Cooperative Soil Survey
U.S.A.