LOCATION THROCK             TX

THROCK SERIES

The Throck series consists of soils that are moderately deep and deep over claystone bedrock or dense clay. They are calcareous, well drained, slowly permeable soils that formed in residuum and slope wash from from claystone and siltstone. They are on gently sloping to steep plains on footslopes of ridges. Slopes range from 1 to 30 percent.

TAXONOMIC CLASS: Fine, mixed, active, thermic Vertic Haplustepts

TYPICAL PEDON: Throck clay--rangeland. (Colors are for dry soil unless otherwise stated.)

A--0 to 4 inches; dark grayish brown (10YR 4/2) clay, very dark grayish brown (10YR 3/2) moist; moderate fine and medium granular structure; hard, firm; many fine roots; few worm casts; strongly effervescent; moderately alkaline; clear smooth boundary. (3 to 9 inches thick)

Bw--4 to 11 inches; brown (10YR 5/3) clay, dark brown structure parting to moderate medium granular structure; hard, firm; many fine roots; few very fine pores; few worm casts; few iron-manganese concretions up to 2 millimeters across; few very fine masses of calcium carbonate in lower 2 inches; strongly effervescent; moderately alkaline; clear wavy boundary. (5 to 12 inches thick)

Bk1--11 to 20 inches; brown (10YR 5/3) silty clay, brown (10YR 4/3) moist; moderate coarse and common fine roots; few fine pores; few worm casts; common pressure faces on peds; few intersecting slickensides; few iron-manganese concretions up to 2 millimeters across; 7 percent medium to very fine masses of calcium carbonate; violently effervescent; strongly alkaline; gradual smooth boundary. (8 to 20 inches thick)

Bk2--20 to 34 inches; brown (10YR 5/3) silty clay, brown (10YR 4/3) moist; thick, wedge-shaped peds tilted at 15 to 45 degrees from horizontal parting to moderate coarse blocky structure; extremely hard, very firm; few and very fine roots; common fine pores; few worm casts; few grayish brown stains on surfaces of peds; common iron-manganese concretions up to 2 millimeters across; about 3 percent fine and very fine masses and concretions of calcium carbonate; violently effervescent; moderately alkaline; gradual smooth boundary. (0 to 12 inches thick)

BC--34 to 40 inches; pale brown (10YR 6/3) silty clay, brown (10YR 5/3) moist; thick, weak, wedge-shaped peds 15 to 45 degrees from horizontal parting to weak coarse angular blocky structure; few fine roots; few very fine pores; common iron-manganese concretions up to 2 millimeters across; few very fine filaments and crystals of salt and gypsum on surfaces of peds; few very fine masses and concretions of calcium carbonate; violently effervescent; moderately alkaline; clear wavy boundary. (0 to 19 inches thick)

Cd--40 to 50 inches; grayish brown (2.5Y 5/2) interbedded fractured siltstone and claystone bedrock, dark grayish brown (2.5Y 4/2) moist; weak thin to thick platy rock structure that has vertical fractures every 1/2 to 2 inches with weak angular blocky appearance and very fine cross-bedding planes with grayish brown to light brownish gray (2.5Y 6/2) lamella; few mesquite roots 1 to 10 millimeters across; many iron-manganese concentrations on ped faces; few very fine gypsum and salt crystals on surfaces and in cross-bedding planes; few very fine threads and films of calcium carbonate on faces; noncalcareous matrix; strongly effervescent surfaces; moderately alkaline.

TYPE LOCATION: Shackelford County, Texas; from U.S. Highway 283 in Albany; 4.35 miles west on U.S. Highway 180, 0.35 mile northwest on old paved road, 0.25 mile north on a private road, 500 feet northwest, in rangeland about 180 feet northwest of stock tank dam.

RANGE IN CHARACTERISTICS: Solum thickness ranges from 30 to 60 inches over claystone or siltstone bedrock or dense clay. Clay content of the control section is 35 to 60 percent. Most pedons are calcareous throughout. The surface has 0 to 5 percent stones. Reaction is slightly alkaline or moderately alkaline throughout.

The A horizon has hue of 7.5YR to 2.5Y, value of 4 or 5, and chroma of 2 to 4. It is either too thin or too low in organic matter or both to qualify as a mollic epipedon when moist values are 3. Texture is clay loam, silty clay loam, silty clay or clay. Clay content ranges from 30 to 60 percent. In most pedons, limestone fragments comprise about 1 to 15 percent but range to 30 percent in some pedons.

The Bw or By horizon has hue of 7.5YR to 2.5Y, value of 4 to 6, and chroma of 2 to 4. Texture is silty clay loam, silty clay or clay. Clay content ranges from 35 to 60 percent. Limestone fragments vary from a few to 30 percent and are mostly less than 3 inches in diameter.

The Bk, Bky or BC horizons have hue of 7.5YR to 2.5Y, value of 5 to 7, and chroma of 2 to 7. Texture is silty clay or clay. Clay content ranges from 40 to 60 percent. Calcium carbonate equivalent ranges from 15 to 40 percent.

The Cd horizon is noncemented claystone or siltstone bedrock interbedded with thin beds of limestone bedrock, or massive dense clay or silty clay in shades of gray, olive, yellow or brown. Texture ranges to loam sandy clay loam, or clay loam in some pedons. Clay content is variable, ranging from 25 to 60 percent. Interbedded strata of limestone 2 to 24 inches in thickness occur in most pedons at depths of 40 to 80 inches. Layers of reddish claystone, occur in a few pedons.

COMPETING SERIES: There are no competing series. Similar soils are the Altoga, Berda, Dugout, Ellis, Mangum, Owens, the tentative Tilvern series, Vernon, and Weymouth series. Altoga, Berda, Dugout, and Weymouth soils have less than 35 percent clay in the control section. Also, Altoga and Dugout soils have carbonatic mineralogy. Ellis soils have smectitic mineralogy. Mangum soils have superactive cation exchange activity class, hue of 5YR or redder in the B horizon, and do not have dense shale or clayey more within 60 inches. Owens soils do not have calcic horizons and have sola less than 30 inches thick. Vernon soils have less than 15 percent calcium carbonate equivalent throughout the control section and have hue of 5YR or redder.

GEOGRAPHIC SETTING: Throck soils are on gently sloping to steep plains on footslopes of ridges. Slopes are mainly from 1 to 5 percent, but range up to 30 percent. The soil formed in residuum claystone and siltstone interbedded with limestone. Mean annual precipitation ranges from 22 to 30 inches, and mean annual temperature ranges from 63 to 66 degrees F. Frost free days range from 210 to 240 days, and elevation ranges from 1,250 to 2,250 feet. Thornthwaite P-E indices range from 30 to 44.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the similar Owens series and the Hensley, Lindy, Lueders, Mereta, Speck, and Tobosa series. Hensley, Lindy, Lueders, and Speck soils are underlain by limestone. Also, Hensley, Lueders, and Speck soils have sola less than 20 inches thick. Mereta soils have a petrocalcic horizon. Tobosa soils have gilgai relief and intersecting slickensides.

DRAINAGE AND PERMEABILITY: Well drained. Permeability is slow. Runoff is medium on 1 t 5 percent slopes, high on 5 to 20 percent slopes, and very high on slopes greater than 20 percent.

USE AND VEGETATION: Used for rangeland but a few areas are cultivated and planted to small grain. Native grasses are sideoats grama, blue grama, little bluestem, silver bluestem, buffalograss, and Texas wintergrass.

DISTRIBUTION AND EXTENT: North-central Texas, mainly in the Rolling Limestone Prairie, North Central Prairie and Eastern Part of the Rolling Plains. The series is extensive.

MLRA OFFICE RESPONSIBLE: Temple, Texas

SERIES ESTABLISHED: Baylor County, Texas; 1971.

REMARKS: Classification change from Typic Ustochrepts to Vertic Ustochrepts based on laboratory data from Stephens, Throckmorton and Shackelford Counties. COLE data and slickensides indicate the need for the change. Diagnostic horizons and features recognized in this pedon are:

Ochric Epipedon - 0 to 4 inches. (A horizon)

Cambic horizon - 4 to 11 inches. (Bw horizon)

Calcic horizon - 11 to 20 inches. (Bk1 horizon)

ADDITIONAL DATA; NSSL S80TX-417-001, NSSL S84TX-429-006, and TA&MU S89TX-447-001