LOCATION CLARK FORK MT

Established Series
Rev. RER, SJJ
02/2016

CLARK FORK SERIES

The Clark Fork series consists of very deep, somewhat excessively drained soils that formed in very gravelly and cobbly alluvium derived mainly from granite. These soils are on stream terraces and fan remnants. Slopes are 0 to 25 percent. Mean annual precipitation is about 25 inches (635 mm), and mean annual temperature is about 44 degrees F (6.5 deg. C).

TAXONOMIC CLASS: Sandy-skeletal, mixed, frigid Typic Ustorthents

TYPICAL PEDON: Clark Fork very cobbly sandy loam, forest (colors are for dry soil unless otherwise noted).

Oi--0 to 3 cm; leaf litter and needles.

A--3 to 5 cm; grayish brown (10YR 5/2) very cobbly sandy loam; very dark grayish brown (10YR 3/2) moist; moderate fine granular structure; soft, very friable, nonsticky and nonplastic; 15 percent gravel, 20 percent cobbles; slightly acid (pH 6.5); clear smooth boundary. (1 to 8 cm thick)

Bw--5 to 23 cm; light yellowish brown (10YR 6/4) very cobbly fine sandy loam; dark yellowish brown (10YR 4/4) moist; weak subangular blocky structure; soft, very friable, nonsticky and nonplastic; 15 percent gravel, 20 percent cobbles; slightly acid (pH 6.5); gradual smooth boundary. (15 to 23 cm thick)

C1--23 to 36 cm; very pale brown (10YR 7/4) extremely cobbly loamy fine sand; light yellowish brown (10YR 6/4) moist; single grain; loose, very friable, nonsticky and nonplastic; 25 percent gravel, 40 percent cobbles; neutral (pH 6.6); clear smooth boundary. (8 to 25 cm thick)

C2--36 to 152 cm; very pale brown (10YR 8/2) extremely cobbly loamy fine sand; single grain; loose, nonsticky and nonplastic; 25 percent gravel; 45 percent cobbles; neutral (pH 6.6).

TYPE LOCATION: Ravalli County, Montana; NE 1/4 of sec. 15 T. 1 S., R. 22 W. (At Blacks Crossing on second or third bench level above the Bitteroot River and Overwhich Creek.)

RANGE IN CHARACTERISTICS:
Soil temperature - 44 to 47 degrees F (6.5-8.0 deg. C).
Moisture control section - between 30 and 90 cm, and frozen from November through March.
Soil phases - cobbly, stony, gravelly

A horizon
Hue: 10YR or 7.5YR
Value: 4, 5, or 6 dry; 3, 4, or 5 moist
Chroma: 2, 3, or 4
Texture: sandy loam, fine sandy loam, coarse sandy loam
Clay content: 5 to 15 percent
Rock fragments: 15 to 65 percent total--5 to 25 percent gravel; 10 to 40 percent cobbles.
Reaction: pH 5.6 to 7.3

AC or Bw horizon
Hue: 10YR or 7.5YR
Value: 5, 6, 7, or 8 dry; 3, 4, 5, or 6 moist
Chroma: 2, 3, 4, or 6
Texture: sandy loam, loamy fine sand
Clay content: 5 to 15 percent
Rock fragments: 15 to 65 percent total --5 to 25 percent gravel, 10 to 40 percent cobbles.
Reaction: pH 5.6 to 7.3

C horizons
Hue: 10YR, 7.5YR, or 2.5Y
Value: 5, 6, or 7 dry; 3, 4, or 5 moist
Chroma: 3, 4, or 6
Texture: loamy sand, loamy fine sand (with less than 50 percent fine and coarser sand)
Rock fragments: 35 to 80 percent total--20 to 30 percent gravel, 15 to 50 percent cobbles and stones.
Reaction: pH 6.1 to 7.3

COMPETING SERIES:
Hopdraw (SD) - carbonates throughout the profile.
Nakaibito (AZ) - not frozen November through March but are moist in some part.
Nemote (MT) - horizons that have lamellae that range from 1/4 inch to 1 inch thick.
Oraid (MT) - a lithic contact at depths of 20 to 40 inches.
Quamon (CO) - calcareous throughout the profile.
Rochester (MT) - more than 50 percent fine and coarser sand in particle-size control section; a stony control section.
Tinsley (MT) - calcareous below the A horizon; lime casts on the rock fragments.

GEOGRAPHIC SETTING:
Landform - stream terraces, fan remnants.
Slopes - 0 to 25 percent.
Parent material - very gravelly and cobbly alluvium derived from granite.
Climate - cold winters; moist springs; warm summers.
Mean annual precipitation - 16 to 25 inches (406-635 mm).
Mean annual air temperature - 42 to 45 degrees F. (5.5-7.0 deg. C)
Frost-free period - 90 to 115 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Leadville, Nordicol and Pescar soils. Leadville and Nordicol soils are finer textured and have argillic horizons. Pescar soils are flooded and have aquic conditions.

DRAINAGE AND PERMEABILITY: Somewhat excessively drained; rapid permeability.

USE AND VEGETATION: Clark Fork soils are used mainly for forest and timber. Hay and irrigated crops are grown in small areas.

DISTRIBUTION AND EXTENT: Clark Fork soils are of small extent in high valleys in the northern Rocky Mountains of Montana and similar areas in southwestern Colorado.

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

SERIES ESTABLISHED: Ravalli County, Montana; soil survey area of the Bitteroot Valley area, 1951.

REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon; 0 to 23 cm (O, A, Bw horizons)
Particle-size control section; 25 to 100 cm (C1, C2 horizons)
Clark Fork soils have a frigid temperature regime and an ustic moisture regime that borders on udic. Approximately 1,800 acres have been classified in Colorado.

National Cooperative Soil Survey
U.S.A.