Soil Survey of Sweet Grass County Area, Montana - Soil Data Mart

Sweet Grass County Area, Montana—Part I 45
Landform: Fan, landslide, moraine, mountain, terrace,
and fan on mountain
Parent material: Silty and clayey alluvium or till
Slope range: 2 to 45 percent
Elevation range: 5,500 to 7,500 feet
Mean annual precipitation: 20 to 25 inches
Mean annual air temperature: 36 to 38 degrees F
Frost-free period: 50 to 70 days
Taxonomic Class: Fine, mixed, superactive Ustic
Argicryolls
Typical Pedon
Bridger cobbly clay loam, in an area of Tibson,
extremely bouldery-Bridger, extremely bouldery-
Adel complex, 8 to 35 percent slopes, in an area
of rangeland, 2,200 feet north and 800 feet east
of the southwest corner of sec. 2, T. 3 S., R. 12 E.;
USGS McLeod Basin topographic quadrangle
(lat. 45 o 36'08" N.; long. 110 o 12'50" W.)
A—0 to 8 inches; dark gray (10YR 4/1) cobbly clay
loam, very dark gray (10YR 3/1) moist; moderate
very fine and fine granular structure; soft, very
friable, slightly sticky, slightly plastic; common
very fine to medium roots; many very fine and
fine pores; 10 percent gravel; 10 percent cobbles;
slightly acid (pH 6.4); clear smooth boundary.
Bt1—8 to 12 inches; light brownish gray (10YR 6/2)
clay loam, dark grayish brown (10YR 4/2) moist;
strong very fine and fine subangular blocky
structure; moderately hard, firm, moderately
sticky, moderately plastic; common very fine to
medium roots; common very fine and fine pores;
common distinct discontinuous dark grayish
brown (10YR 4/2) moist; clay films on faces of
peds; 5 percent gravel; 5 percent cobbles; slightly
acid (pH 6.2); clear smooth boundary.
Bt2—12 to 19 inches; dark grayish brown (2.5Y 5/2)
clay, very dark grayish brown (2.5Y 4/2) moist;
strong medium prismatic structure parting to
strong medium subangular blocky; very hard,
very firm, very sticky, very plastic; common very
fine to medium roots; few very fine and fine pores;
many prominent continuous dark yellowish brown
(2.5Y 4/2) moist; clay films on faces of peds;
5 percent gravel; 5 percent cobbles; neutral
(pH 6.8); clear smooth boundary.
Bt3—19 to 27 inches; light olive brown (2.5Y 5/3)
clay, dark grayish brown (2.5Y 4/2) moist; strong
medium prismatic structure; extremely hard,
extremely firm, very sticky, very plastic; few very
fine and fine roots; few very fine pores; common
prominent continuous dark yellowish brown (2.5Y
4/2) moist; clay films on faces of peds; 5 percent
gravel; 5 percent cobbles; neutral (pH 7.2); clear
smooth boundary.
Btk—27 to 34 inches; grayish brown (2.5Y 5/2) clay
loam, dark grayish brown (2.5Y 4/2) moist; strong
fine and medium subangular blocky structure;
very hard, firm, moderately sticky, moderately
plastic; few very fine and fine roots; few very fine
pores; few distinct patchy dark yellowish brown
(2.5Y 4/2) moist; clay films on faces of peds;
many fine and medium irregular masses of lime;
10 percent gravel; 2 percent subangular cobbles;
strongly effervescent; slightly alkaline (pH 7.8);
clear smooth boundary.
Bk—34 to 60 inches; light brownish gray (2.5Y 6/2)
gravelly clay loam, grayish brown (2.5Y 5/2)
moist; strong fine and medium angular blocky
structure; very hard, firm, moderately sticky,
moderately plastic; few very fine pores; many
fine irregular masses of lime; 10 percent gravel;
5 percent cobbles; violently effervescent; slightly
alkaline (pH 7.8).
Range in Characteristics
Soil temperature: 36 to 47 degrees F
Moisture control section: Between 4 and 12 inches
Thickness of the mollic epipedon: 7 to 16 inches
Depth to the Bk horizon: 17 to 40 inches
Note: Some pedons do not have a Btk horizon.
A horizon
Hue: 7.5YR, 10YR, or 2.5Y
Value: 3 to 5 dry; 2 or 3 moist
Chroma: 1 or 2
Texture (less than 2 mm): Clay loam or loam
Clay content: 18 to 35 percent
Content of rock fragments: 5 to 35 percent—0 to
10 percent stones and cobbles; 5 to 25 percent
gravel
Reaction: pH 6.1 to 7.3
Bt horizons
Hue: 7.5YR, 10YR, or 2.5Y
Value: 5 or 6 dry; 3 to 5 moist
Chroma: 2 to 4
Texture (less than 2 mm): Clay, clay loam, or silty
clay
Clay content: 35 to 50 percent
Content of rock fragments: 5 to 35 percent—0 to
10 percent stones and cobbles; 5 to 25 percent
gravel
Reaction: pH 6.6 to 7.8
Btk horizon
Hue: 7.5YR, 10YR, or 2.5Y
Value: 5 or 6 dry; 4 or 5 moist
Chroma: 2 to 4