LOCATION BIGFORK            OK+AR
Established Series
Rev. JWF:RCB
10/2001

BIGFORK SERIES

The Bigfork series consists of well drained soils that are moderately deep to hard chert that is tilted 35 degrees from horizontal. These moderately permeable soils formed in material weathered from chert or novaculite of Ordovician age. These gently sloping to very steep soils are on ridges of uplands in the Ouachita Mountains land resource area. Slopes are 3 to 60 percent. Mean annual temperature is 62 degrees F., and mean annual precipitation is 48 inches.

TAXONOMIC CLASS: Loamy-skeletal, siliceous, semiactive, thermic Typic Hapludults

TYPICAL PEDON: Bigfork very stony silt loam--forest. (Colors are for moist soil unless otherwise stated.)

Oi--.5 to 0 inch; very dark brown (10YR 2/2) litter of leaves and twigs.

A--0 to 5 inches; yellowish brown (10YR 5/4) very stony silt loam; moderate medium granular structure; hard, friable; common very fine and fine roots inside peds; few medium and coarse roots inside peds; 50 percent chert fragments by volume greater than 76 mm in diameter and 10 percent chert fragments by volume from 2 mm to 76 mm in diameter; strongly acid; clear smooth boundary. (3 to 9 inches thick)

Bt--5 to 35 inches; brown (7.5YR 5/4) very stony silty clay loam; weak fine subangular blocky structure; very hard, friable; common fine roots inside peds; few fine to coarse roots between peds; patchy clay films on faces of peds; 40 percent chert fragments by volume greater than 76 mm in diameter and 10 percent chert fragments by volume from 2 mm to 76 mm in diameter; very strongly acid; abrupt irregular boundary. (18 to 37 inches thick)

R--35 to 40 inches; hard chert bedrock, tilted 35 degrees from a horizontal plane.

TYPE LOCATION: Pushmataha County, Oklahoma; about 4 miles north of Tuskahoma, Oklahoma; 1,100 feet west and 400 feet north of the southeast corner of section 1, T. 2 N., R. 19 E.

RANGE IN CHARACTERISTICS: Solum thickness and depth to hard bedrock ranges from 20 to 50 inches and due to the irregular boundary between the Bt horizon and the underlying tilted bedrock it is extremely variable within short distances.

The A horizon has hue of 7.5YR or 10YR, value of 3 to 5, and chroma of 2 to 4. Where the A horizon has moist value and chroma of 3, it is less than 6 inches thick. Texture is stony, very stony, very gravelly, or extremely gravelly analogues of loam, silt loam, or silty clay loam. Content of chert fragment ranges from 35 to 90 percent by volume. About 15 to 30 percent by volume is 2 mm to 76 mm in diameter and 20 to 60 percent by volume is greater than 76 mm in diameter. Reaction ranges from slightly acid to strongly acid. Some pedons have E horizons from 2 to 8 inches thick. The E horizon is similar to the A horizon in texture, reaction, and content of chert fragments. Colors are 1 or 2 values and chroma higher than the A horizon.

The Bt horizon has hue of 5YR to 10YR, value of 3 to 5, and chroma of 4 to 8. Texture is stony, very stony, very gravelly or extremely gravelly analogues of clay loam or silty clay loam. Content of chert fragments are similar to the A horizon. Reaction ranges from medium acid to very strongly acid.

The R layer is hard chert or novaculite bedrock that is tilted 20 to 60 degrees from horizontal.

COMPETING SERIES: These are the Avant, Cobstone, Lillington, Saffell, and Zafra series in the same family. Avant soils are underlain by an R/C horizon and can be dug with power equipment. Cobstone soils are very deep. Lillington soils have sola greater than 60 inches thick. Saffell soils are deeper than 40 inches to bedrock. Zafra soils are underlain with hard sandstone and typically have redder hue in the Bt horizon.

GEOGRAPHIC SETTING: Bigfork soils are on gently sloping to very steep tops of the hills or ridges of the Ouachita Mountains. These soils formed in material weathered from chert or novaculite of Ordovician age. Slopes range from 3 to 60 percent. Mean annual precipitation ranges from 42 to 56 inches and is evenly distributed throughout the year. Mean annual temperature ranges from 57 to 64 degrees F. Frost free days range from 200 to 220. Thornthwaite annual P-E indices range from 70 to 76. Elevation ranges from 800 to 1400 feet.

GEOGRAPHICALLY ASSOCIATED SOILS: This includes the Avant, Bengal, Bismarck, and Yanush series. The Avant and Bismarck soils occur on similar landscapes. Bengal and Yanush soils occur on foot slopes.

DRAINAGE AND PERMEABILITY: Bigfork soils are well drained. Runoff is rapid or very rapid and permeability is moderate.

USE AND VEGETATION: Used mainly for growing trees. The main trees are post oak and blackjack oak with small amounts of
shortleaf pine.

DISTRIBUTION AND EXTENT: Ouachita Mountains of Oklahoma and possibly in Arkansas. The series is of moderate extent.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Temple, Texas

SERIES ESTABLISHED: Pushmataha County, Oklahoma; 1977.

REMARKS: These soils were formerly included in the Bodine series.

Diagnostic horizons and features recognized in the series are:

Ochric epipedon- the zone from the surface of the soil to a depth of 5 inches (A horizon); Argillic horizon- the zone from 5 to 35 inches (Bt horizon);
Udic moisture regime.
Lithic contact at 35 inches.

ADDITIONAL DATA: Oklahoma State University Data for two pedons. Sample Numbers 70-OK-64-2 and 70-OK-64-3.


National Cooperative Soil Survey
U.S.A.