LOCATION FORTLOGAN               MT

Tentative Series
Rev. SPV-EMM
11/2012

FORTLOGAN SERIES

The Fortlogan series consists of deep, well drained soils that formed in residuum or alluvium over residuum weathered from mudstone and siltstone. These soils are on hills, fan remnants, and structural benches. Slopes are 0 to 15 percent. Mean annual precipitation is about 320 mm, and mean annual temperature is about 6 degrees C.

TAXONOMIC CLASS: Fine-loamy, mixed, superactive, frigid Calcidic Argiustolls

TYPICAL PEDON: Fortlogan loam, rangeland (colors are for dry soil unless otherwise noted).

A--0 to 16 cm; brown (10YR 4/3) loam, dark brown (10YR 3/3) moist; weak fine granular structure; soft, friable, slightly sticky and slightly plastic; common very fine and fine roots; common very fine and fine irregular pores; 5 percent gravel; slightly alkaline (pH 7.6); clear smooth boundary. (10 to 25 cm thick)

Bt--16 to 35 cm; brown (10YR 5/3) clay loam, brown (10YR 4/3) moist; moderate medium subangular blocky structure; hard, friable, moderately sticky and moderately plastic; common very fine and fine roots; common fine tubular pores; 15 percent distinct clay films on faces of peds; 5 percent gravel; slightly alkaline (pH 7.7); clear wavy boundary. (15 to 30 cm)

Bk--35 to 76 cm; light yellowish brown (10YR 6/4) loam, yellowish brown (10YR 5/4) moist; weak fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine and fine roots; few fine and very fine irregular pores; 5 percent gravel; 2 percent fine carbonate masses; strongly effervescent; moderately alkaline (pH 8.4); clear smooth boundary. (35 to 70 cm thick)

BCk--76 to 115 cm; brown (7.5YR 5/4) sandy loam, brown (7.5YR 4/4) moist; massive; soft, friable, slightly sticky and non plastic; few fine roots; few fine irregular pores; 2 percent fine carbonate masses; strongly effervescent; moderately alkaline (pH 8.2); gradual wavy boundary. (0 to 60 cm thick)

C--115 to 135 cm; brown (7.5YR 5/4) paragravelly sandy loam, brown (7.5YR 4/4) moist; massive; soft, very friable, slightly sticky and nonplastic; 20 percent paragravel; finely disseminated carbonates; strongly effervescent; moderately alkaline (pH 8.0); abrupt wavy boundary.

Cr--135 to 152 cm; semi-consolidated mudstone derived from tertiary lake sediments.

TYPE LOCATION: Meagher County, Montana; about 4 miles southeast of former Fort Logan; 3,350 feet west and 4,750 feet north from the SE corner of Sec. 16, T. 10N., R. 5E; Whitetail Reservoir topographic quadrangle. UTM 12T 0491609E, 516492N.

RANGE IN CHARACTERISTICS:

Mean annual soil temperature - 4 to 8 degrees C.
Depth to paralithic contact - 100 to 150 cm.
Depth to argillic horizon - 10 to 25 cm.
Depth to calcic horizon - 25 to 45 cm.

A horizon
Hue: 10YR or 2.5Y
Value: 3 to 5 dry; 2 or 3 moist
Chroma: 2 or 3 dry or moist
Texture: loam or sandy loam
Clay content: 12 to 27 percent
Rock fragments: 5 to 25 percent total -- 5 to 20 percent gravel, 0 to 10 percent cobbles, 0 to 5 percent stones
Reaction: pH 6.8 to 7.8

Bt horizon
Hue: 10YR or 2.5Y
Value: 4 to 6 dry; 3 or 4 moist
Chroma: 2 to 4 dry or moist
Texture: clay loam or sandy clay loam
Clay content: 22 to 35 percent
Rock fragments: 5 to 20 percent total--5 to 15 percent gravel, 0 to 5 percent cobbles
Reaction: pH 6.8 to 7.8

Bk horizon
Hue: 7.5YR to 2.5Y
Value: 4 to 7 dry; 4 to 6 moist
Chroma: 3 or 4 dry or moist
Texture: sandy loam or loam
Clay content: 12 to 27 percent
Rock fragments: 0 to 35 percent gravel, 0 to 5 percent cobbles
Calcium carbonate equivalent: 15 to 30 percent
Reaction: pH 7.8 to 8.4

BCk horizon
Hue: 7.5YR to 2.5Y
Value: 4 to 7 dry; 4 to 6 moist
Chroma: 3 or 4 dry or moist
Texture: sandy loam or loam
Clay content: 10 to 20 percent
Rock fragments: 0 to 25 percent gravel
Calcium carbonate equivalent: 5 to 25 percent
Reaction: pH 7.8 to 8.4

C horizon
Hue: 7.5YR to 2.5Y
Value: 5 to 8 dry; 4 to 6 moist
Chroma: 3 to 6 dry or moist
Texture: sandy loam, or loamy sand
Clay content: 8 to 20 percent
Rock fragments: 0 to 35 percent paragravel
Calcium carbonate equivalent: 5 to 25 percent
Reaction: pH 7.8 to 8.4

COMPETING SERIES:

Beavwan (MT) - are ver deep
Cortyzack (CO) - are very deep
Eldgin (UT) - are very deep
Emlin (CO) - are very deep
Hysoop (MT) - are very deep
Morval (NM) - are very deep
Notter (UT) - are very deep
Nuley (MT) - are very deep
Thunderhead (MT) - are moderately deep
Varney (MT) - are very deep
Villa Grove (CO) - are very deep

GEOGRAPHIC SETTING:

Landform - hills, fan remnants, and structural benches
Elevation - 1,375 to 1,650 meters
Slope - 0 to 35 percent
Parent material - residuum or alluvium over residuum
Climate - long, cold winters; moist springs; warm summers
Mean annual precipitation - 255 to 355 mm
Mean annual temperature - 4 to 7 degrees C
Frost-free season - 70 to 90 days

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Varney and Coyoteflats soils. Varney and Coyoteflats soils are both very deep and occur on similiar landforms as the Fortlogan soils.

DRAINAGE AND PERMEABILITY: Well drained; moderate permeability.

USE AND VEGETATION: Fortlogan soils are used mainly for rangeland. Potential native vegetation is bluebunch wheatgrass, needleandthread, prairie junegrass, rubber rabbitbrush, broom snakeweed, and phlox.

DISTRIBUTION AND EXTENT: Fortlogan soils are of small extent in the intermountain valleys in southwestern Montana. MLRA 44B.

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

SERIES PROPOSED: Meagher County Area, Montana, 2011. Fortlogan is named after the nearby decommissioned U.S. Army Fort.

REMARKS: Diagnostic horizons and features recognized in this pedon are:

Mollic epipedon - the zone from 0 to 18 when mixed (A and part of Bt horizon)
Argillic horizon - the zone from 16 to 35 cm (Bt horizon)
Calcic horizon - the zone from 35 to 115 cm (Bk and BCk horizons)
Paralithic contact - at 135 cm (Cr horizon)

Fortlogan soils have a frigid temperature regime and an ustic moisture regime bordering on aridic.

Taxonomic version: Eleventh Edition, 2010

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National Cooperative Soil Survey
U.S.A.