LOCATION ROCKPENS TXEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, thermic Sodic Ustic Haplocambids
TYPICAL PEDON: Rockpens sandy loam - rangeland. (Colors are for dry soil unless otherwise stated.)
A--0 to 3 inches; brown (7.5YR 5/3) sandy loam, brown (7.5YR 4/3) moist; moderate medium and coarse subangular blocky parting to moderate fine subangular blocky structure; slightly hard, very friable; slightly sticky, and slightly plastic; common very fine and fine roots; few very fine tubular pores; 5 percent rounded ignimbrite gravel; 1 percent calcium carbonate equivalent; strongly effervescent; nonsaline; slightly alkaline; clear smooth boundary (3 to 5 inches thick).
Bn1--3 to 14 inches; brown (7.5YR 5/3) gravelly loam, brown (7.5YR 4/3) moist; moderate medium and coarse subangular blocky parting to moderate fine and medium subangular blocky structure ; slightly hard, friable, slightly sticky, and slightly plastic; common very fine, fine, medium, and coarse roots; few very fine tubular pores; 15 percent rounded ignimbrite gravel; few distinct patchy white (10YR 8/1) coatings of calcium carbonate on rock fragments; few fine white (10YR 8/1) calcium carbonate threads between peds; 6 percent calcium carbonate equivalent; violently effervescent; nonsaline; moderately alkaline; clear smooth boundary (6 to 12 inches thick).
Bn2--14 to 27 inches; brown (7.5YR 5/3) gravelly loam, brown (7.5YR 4/3) moist; weak medium and coarse subangular blocky parting to weak fine and medium subangular blocky structure; slightly hard, friable, slightly sticky, and slightly plastic; common very fine and fine roots; common fine interstitial pores and few fine tubular pores; 20 percent rounded ignimbrite gravel, and 5 percent subrounded ignimbrite cobbles; common distinct discontinuous white (10YR 8/1) coatings calcium carbonate on rock fragments; few fine white (10YR 8/1) calcium carbonate threads between peds and common medium irregular white (10YR 8/1) masses of calcium carbonate throughout; 8 percent calcium carbonate equivalent; violently effervescent; nonsaline; moderately alkaline; clear smooth boundary (0 to 15 inches thick).
Cn1--27 to 36 inches; reddish brown (5YR 5/3) extremely gravelly loamy sand, reddish brown (5YR 4/3) moist; single grain; soft, very friable, nonsticky, and nonplastic; common very fine and fine roots; many fine interstitial pores; 60 percent rounded ignimbrite gravel, and 10 percent subrounded ignimbrite cobbles; few distinct discontinuous white (10YR 8/1) coatings of calcium carbonate on rock fragments; 2 percent calcium carbonate equivalent; strongly effervescent; very slightly saline; moderately alkaline; gradual wavy boundary.
Cn2--36 to 52 inches; reddish brown (5YR 5/3) extremely gravelly coarse sandy loam, reddish brown (5YR 4/3) moist; single grain; loose, very friable, nonsticky, and nonplastic; few very fine and fine roots; many fine interstitial pores; 75 percent rounded ignimbrite gravel, and 10 percent subrounded ignimbrite cobbles; few distinct discontinuous white (10YR 8/1) coatings of calcium carbonate on rock fragments; 2 percent calcium carbonate equivalent; strongly effervescent; very slightly saline; slightly alkaline; abrupt wavy boundary.
Cn3--52 to 69 inches; reddish brown (5YR 5/3) extremely gravelly coarse sandy loam, reddish brown (5YR 4/3) moist; single grain; loose, very friable, nonsticky and nonplastic; few very fine and fine roots; many fine interstitial pores; 50 percent rounded ignimbrite gravel, 10 percent subrounded ignimbrite cobbles, and 5 percent subrounded ignimbrite stones; few distinct discontinuous white (10YR 8/1) coatings of calcium carbonate on rock fragments; 6 percent calcium carbonate equivalent; strongly effervescent; very slightly saline; slightly alkaline; abrupt smooth boundary (combined thickness of C horizons is 35 to 60 inches).
2Crk--69 to 80 inches; weathered tuffaceous bedrock; cracks and fractures are more than 4 inches apart; few very fine and fine roots in cracks; common fine and medium irregular white (10YR 8/1) masses of calcium carbonate in cracks; violently effervescent.
TYPE LOCATION: Brewster County, Texas; from the junction of U.S. Highway 90 and Texas Highway 118 in Alpine, 41.1 miles south on Texas Highway 118, 4.25 miles west on ranch road, 0.8 mile south, 3.5 miles west, 0.7 mile south, 100 feet west of road in rangeland. (Latitude: 29 degrees, 47 minutes, 06 seconds North; Longitude: 103 degrees, 43 minutes, 54 seconds West; NAD 1927); Straddlebug Mountain USGS 7.5 minute quadrangle.
RANGE IN CHARACTERISTICS:
Soil moisture: ustic aridic soil moisture regime
Solum thickness: 20 to 40 inches
Depth to weathered tuff bedrock: 60 to more than 80 inches
Clay content in the control section: 12 to 25 percent
Rock fragments: 35 to 60 percent ignimbrite
Sodium adsorption ratio: 13 to 30 percent throughout the pedon
Ignimbrite gravel, cobbles, and stones cover 35 to 95 percent of the surface
A horizon
Hue: 7.5YR, 10YR
Value: 5 through 7 dry, 4 moist
Chroma: 2 through 4, dry or moist
Texture: sandy loam, but ranges to loam, sandy clay loam
Clay content: 10 to 25 percent
Ignimbrite rock fragments: 5 to 25 percent
Reaction: slightly alkaline or moderately alkaline
Bn horizons
Hue: 5YR, 7.5YR, 10YR
Value: 5 through 7 dry, 4 moist
Chroma: 3 or 4, dry or moist
Texture: loam, sandy loam
Clay content: 12 to 18 percent
Ignimbrite rock fragments: 15 to 50 percent
Calcium carbonate in the form of masses, films, and threads range from none to few; most visible forms of secondary calcium carbonate occur as coatings on coarse fragments
Calcium carbonate equivalent: 1 to 5 percent
Reaction: moderately alkaline
Cn horizon
Hue: 5YR, 7.5YR, 10YR
Value: 5 through 7 dry, 4 moist
Chroma: 2 through 4, dry or moist
Texture: loamy sand, coarse sandy loam, sandy loam
Clay content: 10 to 18 percent
Rock fragments: 50 to 85 percent
Calcium carbonate coatings on coarse fragments range from few to many
Calcium carbonate equivalent: 1 to 15 percent
Gypsum: crystals occur in some pedons
Reaction: moderately alkaline
Cr horizon
Tuffaceous bedrock of the Duff and Pruett Formations
Gypsum crystals occur in some pedons.
COMPETING SERIES: There are no competing series
GEOGRAPHIC SETTING: Rockpens soils are on late-Pleistocene stream terraces. Slopes range from 1 to 3 percent and are plane to convex in shape. The soil formed in alluvium derived predominantly from tuffaceous sediments of the Duff and Pruett Formations, with rock fragments derived from the Mitchell Mesa Ignimbrite. Mean annual precipitation is 8 to 14 inches, with most occurring from July through September. Mean annual air temperature is 64 to 68 degrees F. Frost-free period ranges from 210 to 280 days. Elevation ranges from 2,500 to 4,500 feet.
GEOGRAPHICALLY ASSOCIATED SOILS: These include the Beewon, Borunda, Musgrave, Quadria, and Straddlebug series. Beewon and Quadria soils are on mid-Pleistocene pediments and have argillic horizons with more than 35 percent clay and less than 35 percent coarse fragments. Borunda soils are moderately deep to tuffaceous bedrock, are in the fine-loamy family, and have calcic and gypsic horizons. Borunda soils occur on higher erosional slopes and pediments. Musgrave soils are very shallow or shallow to tuffaceous bedrock, are in the clayey family, and are on higher erosional scarps and uplands. Straddlebug soils are on lower Holocene-age alluvial flats and floodplains.
DRAINAGE AND PERMEABILITY: Well drained. Permeability is moderate. Runoff is very low.
USE AND VEGETATION: This soil is used as livestock grazing. The native vegetation consists of black grama, bush muhly, sideoats grama, blue grama, plains bristlegrass, Arizona cottontop, and cane bluestem. The woody species consist of range ratany, creosotebush, and fourwing saltbush.
DISTRIBUTION AND EXTENT: Trans-Pecos Texas in the Southern Desertic Basins, Plains, and Mountains (MLRA 42), Desert Grassland vegetative zone. The soil is of minor extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Phoenix, Arizona
SERIES ESTABLISHED: Brewster County, Texas; 1997. The name is from a rock corral near the type location.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - the zone from 0 to 3 inches (A horizon)
Cambic horizon - the zone from 3 to 27 inches (Bn1 and Bn2 horizons)
Paralithic contact - the boundary at 69 inches (2Crk horizon)
Sodic feature - Sodium adsorption ratio of greater than 13 within a horizon that is at least 10 inches thick within the upper 40 inches of the pedon.
Ustic feature - The soil has an aridic moisture regime that borders on the ustic regime.
Soils classified according to Soil Taxonomy, Second Edition, 1999; Keys to Soil Taxonomy, Tenth Edition, 2006
Updates and revisions for the recorrelation of Brewster County, Texas, Main Part, 2/12/2008, CEM