LOCATION RIOCONCHO               TX

Established Series
Rev. CCW-MLG-ACT
12/2013

RIOCONCHO SERIES

The Rioconcho series consists of very deep, moderately well drained, slowly permeable soils that formed in clayey or silty alluvium derived from limestone. These nearly level soils occur on flood plain steps of river valleys or dissected plateaus. Slopes range from 0 to 2 percent. Mean annual precipitation is about 533 mm (21 in) and the mean annual air temperature is about 18 degrees C (64 degrees F).

TAXONOMIC CLASS: Fine, mixed, superactive, thermic Torrertic Haplustolls

TYPICAL PEDON: Rioconcho clay loam--rangeland.
(Colors are for dry soil unless otherwise stated).

A1--0 to 36 cm (0 to 14 in); dark grayish brown (10YR 4/2) clay loam, very dark brown (10YR 2/2) moist; weak fine granular and moderate very fine subangular blocky structure; hard, firm, but crushes easily to granules, sticky, and plastic; many fine roots; few fine pores; few wormcasts; strongly effervescent; moderately alkaline; gradual wavy boundary.

A2--36 to 91 cm (14 to 36 in); dark grayish brown (10YR 4/2) clay loam, very dark grayish brown (10YR 3/2) moist; moderate fine and medium angular blocky structure; very hard, firm, but crushes easily to granules, sticky, and plastic; few fine roots, few fine pores and wormcasts; strongly effervescent; moderately alkaline; diffuse wavy boundary. Combined thickness of the A horizon is 40 to 102 cm (16 to 40 in)

Bk--91 to 203 cm (36 to 80 in); light brown (7.5YR 6/4) clay loam; brown (7.5YR 5/4) moist; weak fine angular blocky structure; very hard, friable, sticky, and plastic; few fine roots; patchy thin coatings of calcium carbonate on surfaces of peds, and threads of calcium carbonate in pores above 70 inches; strongly effervescent; moderately alkaline.

TYPE LOCATION: Tom Green County, Texas; about 10 miles northwest of San Angelo on U.S. Highway 87, then 1.5 miles south on Texas Highway 2288, then 0.1 mile east in rangeland.
USGS topographic quadrangle: Mount Nebo, TX; Latitude: 31 degrees, 32 minutes, 25.39 seconds N; Longitude: 100 degrees, 33 minutes, 26.70 seconds W; Datum: WGS84.

RANGE IN CHARACTERISTICS:
Soil Moisture: Aridic-ustic soil moisture regime
Solum thickness: 183 to greater than 203 cm (72 to > 80 inches)
Depth to limestone bedrock, gravel, or sand: 1.8 to 7.3 meters (6 to 24 feet)
Organic matter content: has an irregular decrease with depth
Linear extensibility: greater than 6 cm (0.24 in) in the top 100 cm (40 in)
Cracks: 8 to 25 mm wide (0.3 to 1 in) extend from the surface to a depth of more than 51 cm (20 in)

Particle-size control section (weighted average):
Clay content: 35 to 55 percent
Rock fragments: 0 to 25 percent; limestone and quartz; gravel, cobbles, and stones

A horizon
Hue: 7.5YR or 10YR
Value: 3 to 5
Chroma: 1 to 3
Texture: silty clay loam, clay loam, silty clay
Clay content: 35 to 55 percent
Rock fragments: 0 to 15 percent total; 0 to 10 percent gravel, 0 to 5 percent cobbles, 0 to 2 percent stones; Limestone and quartz
Calcium carbonate equivalent: 1 to 30 percent
Effervesence: none to strong
Reaction: slightly alkaline to moderately alkaline

Bw horizon (where present)
Is similar to the Bk horizon but lacking secondary calcium carbonate.

Bk horizon
Hue: 7.5YR or 10YR
Value: 5 to 7
Chroma: 1 to 3
Texture: clay, silty clay, clay loam, silty clay loam
Clay content: 35 to 55 percent
Rock fragments: 0 to 25 percent total; 0 to 15 percent gravel, 0 to 10 percent cobbles, 0 to 5 percent stones; Limestone, quartz, and caliche; some strata below 100 cm (40 in) may contain upto 40 percent fragments.
Calcium carbonate equivalent: 5 to 30 percent
Effervesence: slight to strong
Reaction: slightly alkaline to moderately alkaline

COMPETING SERIES: There are no competing series in the same family. Closely similar series are the Dev, Iraan, Oakalla, Rio Diablo, and Vanderpool.
Dev: has a loamy-skeletal particle-size control section
Iraan: has a fine-silty particle-size control section
Oakalla: has a fine-loamy particle-size control section and is in the typic-ustic moisture regime
Rio Diablo: has lower COLE values and does not have vertic features
Vanderpool: has a fine-loamy particle-size control section and is in the typic-ustic soil moisture regime

GEOGRAPHIC SETTING:
Parent Material: calcareous silty and clayey alluvium derived from limestone
Landscape: River valleys or dissected plateaus
Landform: flood-plain steps
Slope: 0 to 2 percent
Mean annual precipitation: 406 to 610 mm (16 to 24 in)
Thornthwaite P.E. indices: 22 to 34
Mean annual air temperature: 16 to 20 degrees C (62 to 68 degrees F)
Frost-free period: 210 to 240 days
Elevation: 427 to 805 m (1400 to 2650 ft)

GEOGRAPHICALLY ASSOCIATED SOILS: These are Angelo, Dev, Iraan, Lipan, and Mereta series.
Angelo soils: have a calcic horizon at depths of less than 102 cm (40 in) and occur higher in the landscape.
Dev soils: are in the loamy-skeletal particle-size control section and occur on similar positions.
Iraan soils: have a fine-silty particle-size control section, do not have vertic properties, and occur on similar positions.
Lipan soils: is a vertisol with intersecting slickensides and occur on higher positions.
Mereta soils: are shallow to a petrocalcic horizon and occur on higher positions.

DRAINAGE AND PERMEABILITY: Moderately well drained. Permeability is slow. Runoff is medium. The soil is frequently or occasionally flooded for brief or very brief periods.

USE AND VEGETATION: The major uses are cropland or rangeland. Cultivated crops include cotton, grain sorghum, wheat, and oats. Native rangeland vegetation includes buffalograss, Texas wintergrass, vine mesquite, mesquite, hackberry, and pecan.

DISTRIBUTION AND EXTENT: The Edwards Plateau of Texas; LRR I - Southwest Plateaus and Plains Range and Cotton Region; MLRA 81A - Edwards Plateau, Western Part. The series is extensive.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Temple, Texas

SERIES ESTABLISHED: Tom Green County, Texas; 1971.

REMARKS: The soils were formerly included in the Frio series.

The taxonomy was changed from Vertic Haplustolls to Torrertic Haplustolls because these soils occur in an aridic-ustic soil moisture regime.(2013 THW, RFG)

Edited 12/2013 (RFG-THW): Changed to fabular format and added metric values. Upedated the competing series, geographic setting, and associated soils sections.

Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - 0 to 91 cm (0 to 36 in) (A1 and A2 horizons)
Cambic horizon - 91 to 203 cm (36 to 80 in) (Bk horizon, does not have enough carbonates to be a calcic)
Torrertic feature - Linear extensibility exceeds 6 cm within 100 cm (40 in) of the surface, and the soil has cracks greater than 5 mm that extend from the surface to greater than 50 cm (20 in) and 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 at a depth of 50 cm below the soil surface is higher than 5 degrees C.

ADDITIONAL DATA: The Irion County Soil Survey has engineering index test data published from 1977.

Taxanomic Version: Keys to Soil Taxonomy, 11th Edition, 2010

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National Cooperative Soil Survey
U.S.A.