LOCATION VOLCO TXEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, thermic Lithic Calciustolls
TYPICAL PEDON: Volco very gravelly loam rangeland. (Colors are for dry soil unless otherwise stated.)
A--0 to 4 inches; grayish brown (10YR 5/2) very gravelly loam, very dark grayish brown (10YR 3/2) moist; weak fine platy and subangular blocky structure; slightly hard, friable, many very fine and fine roots; 25 percent igneous and caliche gravel, 10 percent igneous cobbles, and 5 percent igneous stones; strongly effervescent; moderately alkaline; clear smooth boundary (2 to 6 inches thick).
Bk--4 to 9 inches; brown (10YR 5/3) very gravelly loam, dark brown (10YR 3/3) moist; weak fine subangular blocky structure; slightly hard, friable; many fine roots and pores; 35 percent igneous gravel, 10 percent igneous cobbles and 10 percent igneous stones; coarse fragments have thin coatings of calcium carbonate; violently effervescent; moderately alkaline; abrupt irregular boundary (5 to 14 inches thick).
R/Bk--9 to 18 inches; fractured, platy grayish volcanic bedrock; weakly cemented in upper part and strongly cemented below; calcium carbonate coated on surface and in fractures; hard pale brown (10YR 6/3) loamy material in fractures, few fine roots and pores in the loamy material; diffuse boundary (2 to 12 inches thick).
R--18 to 20 inches; platy grayish igneous bedrock, indurated.
TYPE LOCATION: Jeff Davis County, Texas; approximately 4.7 miles north of Valentine; 20 yards south of county road 1/4 mile north of the southeast corner of Section 52, Block 4, GH & SA Ry. Co. Survey. (Latitude: 30 degrees, 38 minutes, 40 seconds North; Longitude: 104 degrees, 27 minutes, 27 seconds West.)
RANGE IN CHARACTERISTICS:
Soil moisture: The moisture control section in normal years is dry in some or all parts for six-tenths or more of the cumulative days per year when the soil temperature exceeds 41 degrees F. Aridic ustic soil moisture regime
Solum thickness and depth to hard bedrock: 6 to 20 inches
Rock fragments: 35 to 80 percent, 15 to 50 percent gravel, 2 to 20 percent cobbles, and 0 to 15 percent stones
A horizon
Hue: 5YR, 7.5YR, 10YR
Value: 4 or 5 dry, 3 moist
Chroma: 2 or 3, dry or moist
Texture: sandy loam, loam, clay loam
Reaction: slightly to moderately alkaline
Bk horizon
colors similar to A horizon
Calcium carbonate equivalent: 20 to 35 percent
Secondary carbonate accumulations: occur as coatings on fragments, threads, films or masses
R/Bk and layers are volcanic bedrock with calcium carbonate coating on the surface and in fractures in the upper part. The lower part is mainly rhyolitic or basaltic volcanic.
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING: Volco soils are on hills or mountains formed by the dissection of igneous materials. Slopes range from 1 percent to about 45 percent. They formed in calcareous loamy sediments that have accumulated in the stony mantle of igneous materials. Underlying bedrock is hard; being mainly of rhyolitic or basaltic volcanic. Mean annual precipitation is 12 to 18 inches the majority comes in the summer months. Mean annual air temperature is 57 to 70 degrees F. Frost-free period is 200 to 240 days and elevation ranges from 4,000 to 5,500 feet.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Boracho, Brewster, Hodgins, Medley, Redona and Santo Tomas soils. Boracho soils have a petrocalcic horizon and are on fan terraces and uplands in lower positions. Hodgins, Medley, Redona and Santo Tomas soils have sola more than 20 inches thick and are on fans or flats in lower positions.
DRAINAGE AND PERMEABILITY: Well drained. Permeability is moderate. Runoff is medium on 1 to 3 percent slopes, high on 3 to 5 percent slopes, and very high on slopes greater than 5 percent.
USE AND VEGETATION: Used exclusively for livestock grazing. Native vegetation consists mainly of short grasses and in places a few desertic shrubs. Grasses are mainly black grama, threeawns, sideoats grama, and blue grama. Shrubs are creosotebush, acacia and catclaw.
DISTRIBUTION AND EXTENT: Southwest Texas in MLRA 42. The series of moderate extent.
MLRA OFFICE RESPONSIBLE: Phoenix, Arizona
SERIES ESTABLISHED: Jeff Davis County, Texas; 1971
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - the zone from 0 to 9 inches (A and Bk horizons)
Calcic horizon - the zone from 4 to 18 inches (Bk and R/Bk horizons)
Lithic contact - the boundary at 18 inches (R horizon)
Soil classified according to Soil Taxonomy, Second Edition, 1999; Keys to Soil Taxonomy, Tenth Edition, 2006.
Update and revisions for recorrelation of Brewster County, Texas, Main Part, 2/12/08, CEM