LOCATION SCOTAL                  TX

Established Series


The Scotal series consists of very shallow and shallow, well drained, moderately permeable soils over slowly permeable tuffaceous bedrock. These gently undulating to very steep soils formed in residuum weathered from white tuffaceous strata of the Duff, Pruett, and Devil Graveyard Formations. They are on hills and scarps. Slopes range from 1 to 70 percent. The mean annual precipitation is about 13 inches and the mean annual air temperature is about 65 degrees F.

TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, calcareous, thermic Lithic Ustic Torriorthents

TYPICAL PEDON: Scotal very gravelly sandy clay loam - rangeland. (Colors are for dry soil unless otherwise stated.)

A--0 to 3 inches; brown (10YR 5/3) very gravelly sandy clay loam, dark brown (10YR 3/3) moist; moderate very fine and fine granular structure; slightly hard, friable, slightly sticky and slightly plastic; common very fine and fine roots; few distinct discontinuous white (10YR 8/1) coatings of calcium carbonate on rock fragments; 50 percent subrounded tuff gravel; 8 percent calcium carbonate equivalent; strongly effervescent; moderately alkaline; clear smooth boundary. (2 to 10 inches)

Bk--3 to 8 inches; yellowish brown (10YR 5/4) very gravelly sandy clay loam, dark yellowish brown (10YR 4/4) moist; weak fine and medium subangular blocky structure; slightly hard, friable, moderately sticky and moderately plastic; common very fine and fine roots; many distinct patchy white (10YR 8/1) coatings of calcium carbonate on rock fragments; 45 percent subrounded tuff gravel; 14 percent calcium carbonate equivalent; violently effervescent; moderately alkaline; abrupt smooth boundary. (3 to 10 inches thick)

R/Bk--8 to 14 inches; white (10YR 8/1) fractured tuffaceous bedrock; fractures are 5 to 7 inches apart and filled with yellowish brown (10YR 5/4) soil material from above; common very fine and fine roots in fractures; abrupt smooth boundary. (0 to 7 inches thick)

R--14 to 60 inches; unweathered tuff bedrock of the Pruett Formation.

TYPE LOCATION: Brewster County, Texas, from the junction of U.S. Highway 90 and Texas Highway 118 in Alpine; 32.3 miles south on Texas Highway 118 to 02 Ranch, 2.65 miles southwest, 300 feet north on ranch road to Whirlwind Spring Corral, site is 300 feet west of road on mid slope of hill in range. Whirlwind Spring USGS 7.5 minute quadrangle. Latitude: 29 degrees, 55 minutes, 5 seconds North; Longitude: 103 degrees, 37 minutes, 12 seconds West; NAD83.


Soil moisture - Intermittently moist in the soil moisture control section during July-September. The soil is moist for less than 90 cumulative days during the growing season in the control section. The soil does not receive significant amounts of moisture in the moisture control section during winter months. Ustic aridic soil moisture regime.

Mean annual soil temperature: 68 to 72 inches

Depth to a lithic contact: 4 to 20 inches

Clay content in the particle-size control section: 18 to 35 percent

Organic carbon content: greater than 2 percent

Rock fragments: 35 to 80 percent white tuffaceous fragments

The soil is calcareous throughout

Calcium carbonate equivalent: 10 to 15 percent

Reaction: moderately alkaline

A and Bk horizons
hue: 10YR, 2.5Y
Value: 3 to 6, dry or moist
Chroma: 2 to 4, dry or moist
Texture: sandy clay loam, but ranges to loam, fine sandy loam, or clay loam

R layer
It is noncalcareous, unweathered white tuff of the Duff and Pruett Formations.

COMPETING SERIES: These include the Bofecillos (TX), Holguin (TX), Sauceda (TX), and Beach (TX) series. Bofecillos soils contain less than 2 percent orgain carbon and less than 5 percent calcium carbonate. Holguin soils contain less than 18 percent clay and less than 2 percent orgain carbon. Sauceda soils contain less than 10 percent calcium carbonate. Beach soils contain less than 2 percent organic carbon.

GEOGRAPHIC SETTING: Scotal soils are on hills and scarps. Slopes range from 1 to 70 percent. These soils formed in residuum weathered from white tuff strata of the Duff, Pruett and Devil Graveyard Formations. Mean annual precipitation is 12 to 15 inches, with most occurring from July through September. Mean annual air temperature is 62 to 67 degrees F. Frost free period is 210 to 250 days, and elevation is 3,500 to 5,000 feet.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Borunda, Gemelo, Holguin, and Reduff soils. Borunda soils are moderately deep to weathered tuff bedrock, have calcic and gypsic horizons, and are in the fine-loamy family. Borunda soils are on adjacent erosional slopes and pediments. Gemelo soils are very deep, have cambic horizons, and are in the coarse-loamy family. They are on lower alluvial fan aprons. Holguin soils are underlain by cemented conglomerate bedrock and occur on ridge caps higher in the landscape. Reduff soils are underlain by red tuff bedrock and are on similar landform positions.

DRAINAGE AND PERMEABILITY: Well drained. Permeability is moderate in the surface layer, and slow in the tuffaceous bedrock. Runoff is medium on 1 to 5 percent slopes, high on 5 to 20 percent slopes, and very high on slopes greater than 20 percent.

USE AND VEGETATION: This soil is used as livestock grazing and wildlife habitat. Native vegetation consists of black grama, sideoats grama, cane bluestem, and green sprangletop. Woody species consist of creosotebush, range ratany, and feather dalea.

DISTRIBUTION AND EXTENT: West Texas. MLRA 42. The series is moderately extensive.


SERIES ESTABLISHED: Brewster County, Texas, 1997. The name is coined from a tuffaceous geological formation.

REMARKS: Diagnostic horizons and features recognized in this pedon are:

Ochric epipedon - the zone from 0 to 8 inches (A and Bk horizons) The soil may meet all requirements for a mollic epipedon, except some part of the epipedon is moist for less than 90 days cumulative in normal years during times when the soil temperature at a depth of 20 inches is 41 degrees F.

Lithic contact - the boundary at 8 inches (R/Bk horizon)

Ustic feature - the soil has an aridic moisture regime that borders on the ustic regime

Entisol feature - The absence of diagnostic subsurface horizons

Superactive cation exchange activity class - CEC to percent clay ratio is 0.60 or greater. This is assumed from the abundant zeolitic minerals in the Duff and Pruett Tuffs, and from laboratory data from similar soils in Presidio County, Texas.

Classified according to Soil Taxonomy, Second Edition, 1999; Keys to Soil Taxonomy, Eleventh Edition, 2010

Series does not have a consistent mappable cambic horizon as determined by field soil scientist. June 2008, LEL.

Series update to clarify differences between competing series, June 2008, Marfa MSSL.

Updated competing series section for the correlation of Hudspeth County, Texas (Main Part) and Culberson County, Texas (Main Part); July, 2012, NMS

Revised for the correlation of Presidio County, Texas ; Oct, 2012, WWJ


National Cooperative Soil Survey