LOCATION VARGAS TXEstablished Series
TAXONOMIC CLASS: Coarse-loamy, mixed, active, hyperthermic Petrocalcic Paleustolls
TYPICAL PEDON: Vargas sandy clay loam rangeland (Colors are for dry soil unless otherwise stated.)
A--0 to 10 inches; grayish brown (10YR 5/2) fine sandy loam, very dark grayish brown (10YR 3/2) moist; weak fine granular and subangular blocky structure; slightly hard, very friable; few fine and very fine roots; few fine pores; few root channels and insect tunnels; mildly alkaline; clear smooth boundary. (8 to 14 inches thick)
Bw--10 to 17 inches; brown (10YR 5/3) fine sandy loam, dark brown (10YR 4/3) moist; weak medium subangular blocky structure; hard, friable; few fine and very fine roots and pores; few root channels and insect tunnels; mildly alkaline; clear smooth boundary. (7 to 14 inches thick)
Bk1--17 to 27 inches; light brownish gray (10YR 6/2) fine sandy loam, grayish brown (10YR 5/2) moist; weak medium subangular blocky structure; hard, friable; few fine roots and pores; few root channels and insect tunnels; few fine threads and segregations of calcium carbonate; strongly effervescent; moderately alkaline; clear smooth boundary. (0 to 11 inches thick)
Bk2--27 to 33 inches pale brown (10YR 6/3) gravelly sandy loam, brown (10YR 5/3) moist; moderate fine subangular blocky structure; hard, friable; few fine roots; about 30 percent by volume concretions and nodules of calcium carbonate and strongly cemented calcareous sandstone and indurated caliche fragments up to 7cm across their long axis; strongly effervescent; moderately alkaline; abrupt wavy boundary. (5 to 7 inches thick)
Bkm--33 to 38 inches; white (10YR 8/2) strongly cemented caliche containing pockets and seams of weakly cemented caliche. (3 to 8 inches thick)
BCk--38 to 60 inches; white (10YR 8/2) weakly cemented caliche; massive but contains a few fractures.
TYPE LOCATION: Brooks County, Texas; from junction of Farm Roads 755 and 430, 5.1 miles north and west on Farm Road 430 to Alta Colorado Ranch entrance, 1.7 miles west on ranch road, 0.6 mile north on ranch road, 2.7 miles west on ranch road, 0.4 mile south along fence and 50 feet east in rangeland.
RANGE IN CHARACTERISTICS: Thickness of the solum is 20 to 40 inches, and corresponds to the depth to the petrocalcic horizon. The soil is mildly or moderately alkaline throughout, but is noncalcareous in the upper 14 to 30 inches. This corresponds to the depth to secondary carbonates.
The A horizon is brown (10YR 5/3) or grayish brown (10YR 5/2). It is fine sandy loam or sandy clay loam.
The Bw horizon is grayish brown (10YR 5/2) or brown (10YR 5/3). It is fine sandy loam or loam with less than 18 percent clay.
The Bk horizon has hue of 10YR, value of 6 or 7, and chroma of 2 or 3. It is fine sandy loam, loam, gravelly loam or gravelly sandy loam. The clay content ranges from 10 to 18 percent. It contains 10 to 30 percent by volume concretions and nodules of calcium carbonate and indurated caliche fragments and the amounts increase with depth. Some pedons contain common strongly cemented calcareous sandstone fragments in the lower part.
The Bkm horizon is white (10YR 8/2) or very pale brown (10YR 8/3, 8/4). It is fractured and consists of cemented or indurated calcium carbonate containing seams and pockets of weakly cemented caliche. The cementation becomes weaker with depth.
COMPETING SERIES: These include the Dant series in the same family and the Hidalgo, Olmos, Pernitas, Pettus, Rehm, Sarnosa, Shiner, and Valco series. Dant soils are formed over clayey marine sediments. All of these soils are calcareous. In addition, Hidalgo soils formed over loamy alluvium. Pernitas soils have Bt horizons. Pettus and Rehm soils have more than 35 percent coarse fragments in their sola. Pettus and Shiner have carbonatic mineralogy. Valco soils have sola less than 20 inches thick.
GEOGRAPHIC SETTING: Vargas soils have plane to slightly concave slopes with gradients of 0 to 1 percent. They formed in calcareous loamy sediments of Pleistocene or Pliocene Age that are somewhat stratified with weakly to strongly cemented layers. Climate is semiarid with mean annual precipitation ranging from 22 to 25 inches. Mean annual temperature is about 73 degrees F. Thornthwaite P-E index ranges from 26 to about 30.
GEOGRAPHICALLY ASSOCIATED SOILS: These include the Comitas, Delmita, proposed Jardin, Nueces and Yturria series. Comitas, Delmita and Nueces soils have argillic horizons and occur on similar surfaces. Yturria soils have mollic epipedons more than 20 inches thick. Jardin soils have sola less than 20 inches thick. Yturria and Jardin soils occur at slightly higher elevations.
DRAINAGE AND PERMEABILITY: Well drained; slow to medium runoff; moderate permeability. The underlying sandstone does not restrict movement of water to lower depths during most rainfall events.
USE AND VEGETATION: Used entirely for rangeland and wildlife habitat. The native vegetation in excellent condition is composed of 90 percent grasses, 5 percent woody plants and 5 percent forbs. In excellent condition mid grasses such as plains bristlegrass, hooded windmillgrass, twoflower trichloris, feathery bluestem, Arizona cottontop and pink pappusgrass dominate. Major forbs include bundleflower, bushsunflower, orange zexmenia and guara. Dominant woody plants are mesquite, whitebrush, blackbrush, spiny hackberry, Condalia spp., lime pricklyash, Texas persimmon and desert yaupon. Amounts of woody species increase during extended periods of overgrazing.
DISTRIBUTION AND EXTENT: Central Rio Grande Plain of Texas. The soils of this series are not extensive; their total acreage is about 2,000 acres.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Temple, Texas
SERIES ESTABLISHED: Brooks County, Texas, 1983. The name is from a small creek.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - the zone from the surface of the soil to a depth of 10 inches (A horizon).
Cambic horizon - the zone from approximately 10 to 27 inches (Bw and Bk1 horizons).
Calcic horizon - the zone from 27 to 33 inches (Bk2 horizon).
Petrocalcic horizon - the zone from 33 to 38 inches (Bkm horizon).