LOCATION FRANCONI MTEstablished Series
TAXONOMIC CLASS: Fine-loamy, mixed, superactive Ustic Glossocryalfs
TYPICAL PEDON: Franconi gravelly sandy clay loam, very bouldery, forested (colors are for dry soil unless otherwise noted).
Oi--2 inches to 0; partially decomposed needles, twigs, and leaves. (1/2 to 3 inches thick)
E--0 to 5 inches; light brownish gray (10YR 6/2) gravelly sandy clay loam, dark grayish brown (10YR 4/2) moist; moderate fine and medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine and fine and few medium roots; many very fine and fine and few medium pores; 5 percent cobbles, 15 percent pebbles; neutral (pH 6.6); clear smooth boundary. (2 to 8 inches thick)
E/Bt--5 to 11 inches; E part (70 Percent) light brownish gray (10YR 6/2) gravelly sandy clay loam, grayish brown (10YR 5/2) moist; Bt part (30 percent) yellowish brown (10YR 5/4) gravelly sandy clay loam, dark yellowish brown (10YR 4/4) moist; moderate fine and medium subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; many very fine and fine and few medium roots; many very fine and few fine interstitial and tubular pores; few faint clay films bridging sand grains in Bt part; 20 percent pebbles; moderately acid (pH 6.0); clear smooth boundary. (0 to 8 inches thick)
Bt/E--11 to 19 inches; Bt part (85 percent) yellowish brown (10YR 5/4) gravelly sandy clay loam, dark yellowish brown (10YR 4/4) moist; E part (15 percent) light brownish gray (10YR 6/2) gravelly sandy clay loam, grayish brown (10YR 5/2) moist; moderate medium and coarse prismatic structure parting to moderate fine and medium subangular blocky; slightly hard, friable, slightly sticky and slightly plastic; many very fine and few fine and medium roots; many very fine and few fine interstitial and tubular pores; many faint clay films on faces of peds and bridging sand grains in Bt part; 20 percent pebbles; slightly acid (pH 6.2); clear wavy boundary. (5 to 10 inches thick)
Bt1--19 to 28 inches; yellowish brown (10YR 5/4) gravelly clay loam, dark yellowish brown (10YR 4/4) moist; moderate medium and coarse prismatic structure parting to strong fine and medium subangular blocky; hard, firm, moderately sticky and slightly plastic; common very fine and few fine and medium roots; many very fine and few fine interstitial and tubular pores; many faint clay films on faces of peds and bridging sand grains; 5 percent cobbles, 25 percent pebbles; moderately acid (pH 5.8); clear wavy boundary.
Bt2--28 to 34 inches; brown (7.5YR 5/4) gravelly clay loam, dark brown 7.5YR 4/4) moist; weak coarse prismatic structure parting to moderate fine and medium subangular blocky; slightly hard, friable, slightly sticky and slightly plastic; few very fine roots; common very fine and few fine interstitial and tubular pores; common faint clay films on faces of peds and bridging sand grains; 20 percent pebbles; moderately acid (pH 6.0); clear smooth boundary. (Combined thickness of Bt horizons is 13 to 25 inches)
Cr--34 to 38 inches; pale brown (10YR 6/3) decomposed granite bedrock (grus) that crushes to very gravelly coarse sand; slightly acid (pH 6.2); gradual wavy boundary.
R--38 inches; hard granite bedrock.
TYPE LOCATION: Jefferson County, Montana; 2,500 feet south and 1,600 feet east of the NW corner of sec. 11, T. 4 N., R. 7 W.
RANGE IN CHARACTERISTICS:
Soil temperature - 38 to 42 degrees F.
Moisture control section - between 4 and 12 inches.
Depth to argillic horizon - 8 to 15 inches.
Depth to Cr horizon - 20 to 38 inches.
Depth to bedrock - 23 to 40 inches.
Surface stones and boulders - 0 to 3 percent.
A thin A horizon and a transitional BC horizon is allowed.
E horizon - Hue: 10YR or 2.5Y
Value: 6 or 7 dry; 4 or 5 moist
Chroma: 2 or 3
Texture: coarse sandy loam or sandy clay loam
Clay content: 10 to 25 percent
Rock fragments: 15 to 50 percent--0 to 20 percent cobbles, 15 to 30 percent pebbles
Reaction: pH 6.1 to 7.3
E/Bt horizon - Hue: 10YR or 2.5Y
Value: E part 6 or 7, Bt part 5 or 6 dry; E part 5 or 6, Bt part 4 or 5 moist
Chroma: 2, 3, or 4
Texture: E part--sandy loam or sandy clay loam
Clay content: 10 to 25 percent
Rock fragments: 10 to 35 percent-- 0 to 10 percent cobbles, 10 to 25 percent pebbles
Reaction: pH 5.6 to 6.5
Bt/E horizon - Hue: 10YR or 2.5Y
Value: Bt part 5 or 6, E part 6 or 7 dry; Bt part 4 or 5, E part 5 or 6 moist
Chroma: 2, 3, or 4
Texture: E part--sandy loam or sandy clay loam
Clay content: 15 to 30 percent
Rock fragments: 10 to 35 percent--0 to 5 percent cobbles, 10 to 30 percent pebbles
Reaction: pH 5.6 to 6.5
Bt horizons - Hue: 7.5YR, 10YR, or 2.5Y
Value: 5 or 6 dry; 4 or 5 moist
Chroma: 3 or 4
Texture: sandy clay loam or clay loam
Clay content: 20 to 35 percent
Rock fragments: 10 to 35 percent--0 to 5 percent cobbles, 10 to 25 percent pebbles
Reaction: pH 5.6 to 6.5
COMPETING SERIES:
Releep (MT) - does not have a lithic contact above a depth of 40 inches.
Uinta (WY) - does not have a lithic contact above a depth of 60 inches.
GEOGRAPHIC SETTING:
Landform - alluvial fans, ridges and sideslopes of mountains.
Elevation - 5,500 to 7,000 feet.
Slope- 4 to 60 percent.
Parent material - colluvium or residuum derived from granite bedrock.
Climate - long, cold winters; cool, moist springs; short, cool summers.
Mean annual precipitation - 18 to 24 inches.
Mean annual air temperature - 36 to 40 degrees F.
Frost-free period - 50 to 70 days.
DRAINAGE AND PERMEABILITY: Well drained, moderate permeability.
USE AND VEGETATION: Franconi soils are primarily used for timber production and wildlife habitat. The potential native vegetation is mainly Douglas fir, lodgepole pine, pinegrass, common snowberry, russet buffaloberry, heartleaf arnica, feather solomonseal, Oregongrape, woodland strawberry, and Kinnikinnick.
DISTRIBUTION AND EXTENT: Franconi soils are of small extent in southwestern Montana.
MLRA OFFICE RESPONSIBLE: Bozeman, Montana
SERIES ESTABLISHED: Jefferson County, Montana, 1998.
REMARKS: Soil interpretation record: MT3076, MT3077. Diagnostic horizons and features recognized in this pedon are: a layer of partially decomposed needles, twigs, and leaves from 2 inches to the mineral soil surface (Oi horizon); an ochric epipedon from the mineral surface to 11 inches (E, E/Bt horizons); an argillic horizon from 11 to 34 inches (Bt/E, Bt1, Bt2 horizons); a layer of decomposed granite (grus) from 34 to 38 inches (Cr horizon); hard granite bedrock at 38 inches (R horizon); a particle-size control section from 11 to 31 inches (Bt/E, Bt1, Bt2 horizons). Franconi soils have a cryic temperature regime and an ustic moisture regime bordering on udic.