LOCATION FRANCONI MT
Established Series
Rev. PEM-JAL-KLS
05/2023
FRANCONI SERIES
The Franconi series consists of moderately deep, well drained soils that formed in colluvium or residuum derived from granite bedrock. These soils are on alluvial fans, ridges and sideslopes of mountains. Slopes are 4 to 60 percent. Mean annual precipitation is about 560 mm, and mean annual air temperature is about 3 degrees C.
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).
Oe--0 to 5 cm; partially decomposed needles, twigs, and leaves. (1 to 8 cm thick)
E--5 to 18 cm; 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 gravel; neutral (pH 6.6); clear smooth boundary. (5 to 20 cm thick)
E/Bt--18 to 33 cm; 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 gravel; moderately acid (pH 6.0); clear smooth boundary. (0 to 20 cm thick)
Bt/E--33 to 53 cm; 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 gravel; slightly acid (pH 6.2); clear wavy boundary. (13 to 25 cm thick)
Bt1--53 to 76 cm; 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 gravel; moderately acid (pH 5.8); clear wavy boundary.
Bt2--76 to 91 cm; 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 gravel; moderately acid (pH 6.0); clear smooth boundary. (Combined thickness of Bt horizons - 33 to 64 cm)
Cr--91 to 101 cm; 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--101 cm; hard granite bedrock.
TYPE LOCATION: Jefferson County, Montana; about 760 meters south and 490 meters east of the NW corner of sec. 11, T. 4 N., R. 7 W.
RANGE IN CHARACTERISTICS:
Mean annual soil temperature--3 to 6 degrees C
Moisture control section--10 to 30 cm
Depth to argillic horizon--20 to 38 cm
Depth to paralithic contact--50 to 97 cm
Depth to lithic contact--58 to 100 cm
Surface stones and boulders--0 to 3 percent
A thin A horizon and a transitional BC horizon may occur in some pedons.
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 fragment content--15 to 50 percent total; 0 to 20 percent cobbles, 15 to 30 percent gravel
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 fragment content--10 to 35 percent total; 0 to 10 percent cobbles, 10 to 25 percent gravel
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 fragment content--10 to 35 percent total; 0 to 5 percent cobbles, 10 to 30 percent gravel
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 fragment content--10 to 35 percent total; 0 to 5 percent cobbles, 10 to 25 percent gravel
Reaction--pH 5.6 to 6.5
COMPETING SERIES:
Releep (MT) - does not have a lithic contact above a depth of 100 cm
Uinta (WY) - does not have a lithic contact above a depth of 150 cm
GEOGRAPHIC SETTING:
Landform--alluvial fans, ridges and sideslopes of mountains
Elevation--1675 to 2125 meters
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--460 to 610 mm
Mean annual air temperature--2 to 4 degrees C
Frost free period--50 to 70 days
GEOGRAPHICALLY ASSOCIATED SOILS: None listed.
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, feathery false lily of the valley, mahonia, woodland strawberry, and kinnikinnick.
DISTRIBUTION AND EXTENT: Franconi soils are of small extent in southwestern Montana; MLRA 43B.
SOIL SURVEY REGIONAL OFFICE (SSRO) 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--0 cm to 5 cm (Oe horizon)
Ochric epipedon--5 to 33 cm
Argillic horizon--33 to 91 cm (Bt/E, Bt1, Bt2 horizons)
A layer of decomposed granite (grus)--91 to 101 cm (Cr horizon)
Lithic contact--101 cm (R horizon)
Particle-size control section--33 to 83 cm (Bt/E, Bt1, Bt2 horizons)
Franconi soils have a cryic temperature regime and an ustic soil moisture regime bordering on udic.
Converted to metric and O horizons were updated to start at zero. Competing series section was not updated. 05/2023
National Cooperative Soil Survey
U.S.A.