LOCATION AMISTAD TXEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, carbonatic, thermic Lithic Petrocalcic Calciustolls
TYPICAL PEDON: Amistad flaggy clay loam--rangeland. (Colors are for dry soil unless otherwise stated.)
A--0 to 6 inches; dark grayish brown (10YR 4/2) flaggy clay loam; very dark grayish brown (10YR 3/2) moist; strong fine granular; slightly hard, friable; few fine roots about 40 percent by volume of channery and flaggy limestone fragments, 15 percent 2 mm to 6 inches and 25 percent 6 to 12 inches across; fragments range from 1/4 to 2 inches thick; most fragments coated with secondary carbonates; calcareous; moderately alkaline; abrupt wavy boundary. (4 to 20 inches thick)
Bkm--6 to 17 inches; white (10YR 8/1) strongly cemented, massive caliche containing a few embedded thin flat fragments of limestone; few fine crevices and solution channels filled with very dark grayish brown loam; clear wavy boundary. (4 to 16 inches thick)
R--17 to 80 inches; flaggy limestone bedrock; flagstones mainly 4 to 24 inches long and 1/4 to 6 inches thick.
TYPE LOCATION: Val Verde County, Texas; 17 miles north of Del Rio on U. S. Highway 277 from its intersection with U. S. Highway 90; crest of the face of vertical road cut on east side of highway.
RANGE IN CHARACTERISTICS: Solum thickness ranges from 4 to 20 inches. Calcium carbonate equivalent of the soil less than 20 mm is 40 to 80 percent.
The A horizon contains 35 to 75 percent by volume of thin, flat fragments of limestone and caliche. The surface is covered with 40 to 90 percent thin flat fragments of limestone and caliche that are less than 15 inches long and less than 3 inches thick. The A horizon is brown (7.5YR 5/2; 10YR 5/3), grayish brown (10YR 5/2), dark grayish brown (10YR 4/2), or dark brown (7.5YR 3/2, 4/2; 10YR 4/3). Texture of the A horizon, exclusive of coarse fragments, is loam or clay loam with a clay content of 22 to 35 percent.
The Bkm horizon has an estimated hardness of 2 through 3 on Moh's scale and is uniformly plugged with carbonates. Some pedons have a Bk horizon, 24 to 36 inches thick, of weakly cemented caliche and limestone below the Bkm horizon.
The underlying bedrock is flaggy limestone, interbedded with flaggy sandstone and ironstone. The flagstones have reddish, grayish, or brownish colors and range in thickness from 1/8 inch to 10 inches and in length from 2 to 72 inches. Depth to limestone bedrock ranges from 8 to 36 inches.
COMPETING SERIES: There are no soils in the same family. Similar soils include the Boracho, Cho, Eckrant, Ector, Jimenez, Kimbrough, Langtry, Lozier, Olmos, Queeny, Real, Talpa, Tarrant, Volco, and Zorra series. Boracho, Eckrant, Kimbrough, Jimenez, Queeny, Talpa, Tarrant, and Volco soils have less than 40 percent calcium carbonate equivalent in the soil fraction less than 20 mm. In addition, Eckrant, Talpa, Tarrant, and Volco soils, as well as Ector, Langtry, and Real soils, lack petrocalcic horizons. Cho soils have less than 35 percent coarse fragments. Jimenez, Olmos, and Zorra soils have mean annual soil temperature more than 72 degrees F. Lozier soils lack mollic epipedons. Eckrant and Tarrant soils have more than 35 percent clay in the fine-earth fraction.
GEOGRAPHIC SETTING: Amistad soils are in undulating to hilly uplands. Slope gradients are mainly 1 to 8 percent but range from 0 to 20 percent. The soils formed from Cretaceous Age flaggy limestone like those of the Boquillas formation. The climate is semiarid. Average annual rainfall ranges from 12 to 20 inches, Thornthwaite P-E indices from 16 to 32, and mean annual temperatures from 67 degrees to 72 degrees F.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing
Ector,
Langtry,
Olmos, and
Zorra series. Ector soils occur at higher elevations along the northern and eastern most occurrence of
Amistad soils. Langtry, Olmos, and Zorra soils are on similar surfaces. Langtry soils are along the western fringes of occurrence of Amistad soils. Olmos and Zorra soils border the southern areas of Amistad soils.
DRAINAGE AND PERMEABILITY: Well drained; medium to rapid runoff; moderate permeability in the A horizon; slow permeability in the petrocalcic horizon.
USE AND VEGETATION: Used for rangeland. Native vegetation is short and mid-grasses, mainly gramas, tridens, and threeawns. Shrubs are juniper, lotebush, dalea, guajillo, blackbrush, and cenizo.
DISTRIBUTION AND EXTENT: Mainly in southwest Texas. Series is of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Temple, Texas
SERIES ESTABLISHED: Val Verde County, Texas; 1979.
REMARKS: These soils were formerly included with the Ector series.
Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - 0 to 6 inches
Petrocalcic horizon - 6 to 17 inches
Lithic contact - 17 inches