LOCATION TWINPEAKS TXInactive Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, thermic, shallow Ustalfic Petrocalcids
TYPICAL PEDON: Twinpeaks gravelly loam in rangeland. (Colors are for dry soil unless otherwise stated)
A--0 to 2 inches; brown (7.5YR 4/4) gravelly loam, dark brown (7.5YR 3/4) moist; weak medium granular structure; slightly hard, very friable; common very fine and fine roots; 30 percent chert gravels; very slightly effervescent; slightly alkaline; abrupt smooth boundary. (0 to 7 inches thick)
Bt1--2 to 11 inches; reddish brown (5YR 4/4) extremely gravelly clay loam, dark reddish brown (5YR 3/3) moist; moderate fine and medium subangular blocky structure; hard, firm; common very fine and fine roots; few patchy clay films on surfaces of peds; 60 percent angular chert gravels 1/2 to 2 inches in diameter; very slightly effervescent; slightly alkaline; clear wavy boundary.
Bt2--11 to 18 inches; reddish brown (2.5YR 4/4) extremely gravelly clay loam, dark reddish brown (2.5YR 3/4) moist; moderate fine subangular blocky structure; hard, firm; common very fine and fine roots; common distinct clay films on surfaces of peds; 70 percent angular chert gravels 1/2 to 3 inches in diameter; slightly effervescent; slightly alkaline; abrupt wavy boundary. (Combined thickness of Bt horizons is 8 to 18 inches)
Bkm--18 to 22 inches; pinkish white (7.5YR 8/2) indurated calcium carbonate that is laminar in the upper 1/4 inch; 50 percent chert and limestone gravels imbedded; violently effervescent; moderately alkaline; abrupt smooth boundary. (4 to 20 inches thick)
Bk1--22 to 43 inches; light red (2.5YR 6/6) extremely gravelly sandy clay loam, red (2.5YR 4/6) moist; moderate fine subangular blocky structure; hard, firm; 65 percent chert and limestone gravels with common prominent pinkish white (7.5YR 8/2) discontinuous calcium carbonate coatings; strongly effervescent; moderately alkaline; clear wavy boundary.
Bk2--43 to 62 inches; light reddish brown (5YR 6/4) extremely gravelly sandy loam, reddish brown (5YR 4/4) moist; weak fine subangular blocky structure; hard, firm; 75 percent chert and limestone gravels with faint discontinuous coatings of calcium carbonate; strongly effervescent; moderately alkaline.
TYPE LOCATION: Brewster County, Texas; from the junction of U.S. Highway 90 and U.S. Highway 385 in Marathon; 6.5 miles south on U.S. Highway 385; 6.25 miles southeast on ranch road; 50 feet south of road in range; Latitude: 30 degrees 3 minutes 11.349 seconds North; Longitude: 103 degrees 11 minutes 25.49 seconds West, NAD 1927; USGS Pena Blanca Mountains topographic quadrangle
RANGE IN CHARACTERISTICS:
Soil moisture: Intermittently moist in some part of the soil moisture control section during July - September. Ustic aridic soil moisture regime.
Soil temperature - 64 to 68 degrees F.
Depth to petrocalcic horizon: 10 to 20 inches.
Particle size control section-
Clay content: 20 to 35 percent
Rock fragment content: 60 to 80 percent gravel size fragments
Calcium carbonate equivalent: 0 to 5 percent
A horizon
Hue: 5YR to 10YR
Value: 3 to 5, dry or moist
Chroma: 2 to 4
Clay content: 15 to 27 percent
Gravel content: 20 to 50 percent gravel size fragments
Calcium carbonate equivalent: 0 to 5 percent
Effervescence: none to very slight
Reaction: slightly alkaline to moderately alkaline
Bt horizons
Hue: 2.5YR to 7.5YR
Value: 3 to 6, dry or moist
Chroma: 2 to 6
Clay content: 20 to 35 percent
Calcium carbonate equivalent: 0 to 5 percent
Gravel content: 60 to 80 percent, and individual horizon may contain less than 50 percent. Control section average more than 60 percent gravel size rock fragments.
Effervescence: very slight to slight
Reaction: slightly alkaline to moderately alkaline
Bkm horizon
Hue: 5YR to 10YR
Value: 7 or 8, dry or moist
Chroma: 1 to 3
Effervescence: strong to violent
Cementation: indurated and laminar in the upper 1/8 to 1/2 inch; the lower part is strongly cemented to indurated,
Rock fragment content: 50 to 80 percent, and individual horizon may contain less than 50 percent. Control section average more than 60 percent gravel size rock fragments.
Bk horizons
Hue: 2.5YR to 7.5YR
Value: 3 to 6, dry or moist
Chroma: 2 to 6
Clay content: 15 to 30 percent
Rock fragment content: 55 to 80 percent, and individual horizon may contain less than 50 percent, control section average more than 60 percent gravel size rock fragments.
Effervescence: strong to violent
Calcium carbonate coats on rock fragments: common to many
COMPETING SERIES: This is the Terino (NM) series. Terino soils average less than 60 percent andesite and rhyolite rock fragment in the particle size control section.
GEOGRAPHIC SETTING: Twinpeaks soils are on alluvial fans and pediments below and adjacent to hills and mountains. The soils formed in very gravelly sediments derived primarily from chert and limestone bedrock. Slopes are dominantly 1 to 8 percent but range up to about 20 percent. The elevation ranges from 3,500 to 4,500 feet. The mean annual temperature ranges from about 60 to 65 degrees F. The mean annual precipitation ranges from 10 to 14 inches with a summer maximum. Frost free period range from 210 to 260 days
GEOGRAPHICALLY ASSOCIATED SOILS: These are Bissett, Bullis, Buckear, Catto, Coyanosa, Paisano, and Stillwell series. Bissett soils are shallow and very shallow to a lithic contact over limestone bedrock. Bullis soils occur on similar landforms, but are very deep and do not have a petrocalcic horizon. Buckear soils are shallow and very shallow to a paralithic contact over shale bedrock. Catto soils are shallow and very shallow to a lithic contact over chert bedrock. Coyanosa soils are shallow and very shallow to lithic contact over sandstone bedrock. Paisano soils occur on similar landforms, but do not contain an argillic horizon. Stillwell occur on alluvial flats below Twinpeaks soils, and do not contain an argillic horizon.
DRAINAGE AND PERMEABILITY: Well drained. Permeability is moderately slow permeable in the upper part and very slow in the petrocalcic horizon. Runoff is very high.
USE AND VEGETATION: Twinpeaks soils are used as rangeland. Dominant woody plants include creosotebush, mariola, javelina bush, whitethorn acacia, mesquite, tarbush, ephedra, and allthorn. Characteristic grasses include black grama, hairy grama, cane bluestem, threeawns, red grama, fluffgrass.
DISTRIBUTION AND EXTENT: Marathon Basin and similar areas of Trans-Pecos Texas. Southern Desertic Basins, Plains, and Mountains, Desert Grassland Ecological zone (MLRA 42). The series is moderately extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Phoenix, Arizona
SERIES ESTABLISHED: Brewster County, Texas, 2003. The name is taken from the Twin Peaks located about 15 miles southeast of Marathon, Texas.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon: The zone from 0 to 2 inches (A horizon)
Argillic horizon: 2 to 18 inches (Bt horizons)
Petrocalcic horizon: 18 to 22 inches (Bkm horizon)
Calcic horizon: 22 to 62 inches (Bk and BCk horizons
Ustic feature: The soil has an aridic moisture regime that borders the ustic regime.
Classified according to Soil Taxonomy Second Edition, 1999; Keys to Soil Taxonomy Tenth Edition, 2006.