LOCATION POTRILLO TXInactive Series
TAXONOMIC CLASS: Coarse-loamy, mixed, superactive, thermic Ustic Haplocalcids
TYPICAL PEDON: Potrillo gravelly sandy loam - rangeland. (Colors are for dry soil unless otherwise stated.)
A--0 to 2 inches; pinkish gray (7.5YR 6/2) gravelly sandy loam, brown (7.5YR 4/2) moist; moderate medium granular structure; slightly hard, very friable; common very fine and fine roots; 20 percent pebbles from mixed sources; strongly effervescent; moderately alkaline; clear smooth boundary. (1 to 7 inches thick)
Bk1--2 to 9 inches; light brown (7.5YR 6/3) gravelly coarse sandy loam, brown (7.5YR 4/3) moist; moderate fine subangular blocky structure; slightly hard, very friable; common very fine and fine roots; few films, threads, and masses of calcium carbonate; 35 percent pebbles from mixed sources with patchy coatings of calcium carbonate on the underside; strongly effervescent; moderately alkaline; clear smooth boundary.
Bk2--9 to 22 inches; light brown (7.5YR 6/3) gravelly sandy loam, brown (7.5YR 4/3) moist; weak fine subangular blocky structure; slightly hard, very friable; few very fine and fine roots; few films, threads, and masses of calcium carbonate; 25 percent pebbles from mixed sources with few thin patchy coatings of calcium carbonate on the underside; strongly effervescent; moderately alkaline; clear smooth boundary.
Bk3--22 to 37 inches; light brown (7.5YR 6/3) gravelly fine sandy loam, brown (7.5YR 4/3) moist; weak medium subangular blocky structure; slightly hard, very friable; 20 percent pebbles from mixed sources with few patchy coatings of calcium carbonate on the undersides; strongly effervescent; moderately alkaline; gradual smooth boundary.
Bk4--37 to 50 inches; light brown (7.5YR 6/4) gravelly sandy loam, brown (7.5YR 4/4) moist; weak medium subangular blocky structure; slightly hard, very friable; 15 percent pebbles from mixed sources with few thin patchy coatings of calcium carbonate; strongly effervescent; moderately alkaline; gradual smooth boundary. (Combined thickness of the Bk is 30 to 80 inches)
BC--50 to 80 inches; light brown (7.5YR 6/4) gravelly coarse sandy loam, brown (7.5YR4/4) moist; weak medium subangular blocky structure; slightly hard, very friable; 20 percent pebbles from mixed sources; strongly effervescent; moderately alkaline.
TYPE LOCATION: Presidio County, Texas; from the junction of U.S. Highway 90 and U.S. Highway 67 in Marfa; 7.2 miles south on U.S. Highway 67; 25 miles southeast on Ranch Road 169 to end of pavement; 3.2 miles south on county road; 7.6 miles east and south on county road; 1.1 miles east on ranch road to junction; 1.1 miles southeast on ranch road to junction; 1.7 miles east on ranch road to junction; 2.9 miles southeast on ranch road to junction; south on ranch road to dirt tank; west across tank dam then 0.5 mile northwest on ranch road; 40 feet west of road in range. (Latitude: 29 degrees, 46 minutes, 25 seconds North; Longitude: 103 degrees, 48 minutes, 10 seconds West.)
RANGE IN CHARACTERISTICS:
Silicate clay content: 10 to 18 percent
Coarse fragments: 15 to 35 percent
Reaction: slightly alkaline or moderately alkaline
Depth to the calcic horizon: 2 to 24 inches
Soil moisture: The soil is intermittently moist in the soil moisture control section during July through September, and does not receive winter precipitation. Ustic aridic moisture regime.
A horizon
Hue: 5YR or 7.5YR
Value: 5 to 7
Chroma: 2 to 4
Texture: coarse sandy loam, sandy loam, fine sandy loam or loam
Calcium carbonate equivalent: 5 to 10 percent
Gravel: 15 to 35 percent
Bk horizon
Hue: 5YR or 7.5YR
Value: 5 to 7
Chroma: 2 to 4
Texture: coarse sandy loam, sandy loam, or fine sandy loam
Gravel: 15 to 45 percent, but average less than 35 percent. Calcium carbonate: occur in the form of films, threads, masses and coatings on coarse fragments range from few to common. Coatings and pendants range from few thin patchy to common patchy
Calcium carbonate equivalent: 10 to 20 percent
BC horizon
Hue: 5YR or 7.5YR
Value: 5 to 7
Chroma: 2 to 4
Texture: coarse sandy loam, sandy loam, or fine sandy loam
Gravel: 15 to 35 percent
Calcium carbonate content: 5 to 10 percent
COMPETING SERIES: This is the Bilgray (AZ), Geta (NV), Kinco (TX), Luckyhills (AZ), and Stronghold (AZ) series. Bilgray soils have dense compacted sediments within 60 inches of the soils surface. Geta soils have less than 15 percent coarse fragments. In addition, Geta soils are in the Mohave Desert (MLRA 30) receive mostly winter precipitation and are usually dry from April through November. Kinco soils calcic horizons at depths between 24 and 40 inches. Luckyhills and Stronghold soils receive winter precipitation in the soil moisture control section.
GEOGRAPHIC SETTING: Potrillo soils are on gently undulating to undulating ridges, fans and fan terraces. Slopes range from 1 to 8 percent. The soil formed in medium to moderately coarse textured alluvial and residual materials. Mean annual precipitation ranges from 10 to 14 inches, and mean annual temperature ranges from 64 to 68 degrees F. Frost free season is 210 to 260 days, and elevation ranges from 3,000 to 4,500 feet.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Bigetty, Chilicotal, Kinco, and Martillo series. Bigetty soils have mollic epipedons and are in a moisture receiving position in drainageways. Chilicotal soils average more than 35 percent coarse fragments in the control section and are on upland ridges and fans. Kinco soils are on nearly level to gently sloping upland plains. Martillo soils are on broad alluvial flats and have more than 35 percent clay in the control section.
DRAINAGE AND PERMEABILITY: Well drained. Permeability is moderately rapid. Runoff is negligible on 1 to 3 percent slopes, very low on 3 to 5 percent slopes, and low on 5 to 8 percent slopes.
USE AND VEGETATION: This soil is in rangeland. Native vegetation consists of mainly drought tolerant short and mid grasses such as black grama, bush muhly, slim tridens, sideoats grama, blue grama, plains bristlegrass, cane bluestem, Arizona cottontop, and tobosa. Woody species consist of creosotebush, and range ratany.
DISTRIBUTION AND EXTENT: Southwest Texas in MLRA 42. The series is of minor extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Phoenix, Arizona
SERIES ESTABLISHED: Brewster County, Texas, 1997. The name is from Puerto Potrillo creek.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - 0 to 2 inches. (A horizon)
Calcic horizon - 2 to 50 inches. (Bk horizons)
Classified according to Soil Taxonomy Second Edition, 1999