Established Series


The Mailtrail series consists of very shallow and shallow soils over a petrocalcic horizon. They are well drained, moderately permeable soils that formed in alluvium of Pleistocene age. These soils are on high stream terraces and fans. Slopes range from 1 to 8 percent.

TAXONOMIC CLASS: Loamy-skeletal, carbonatic, thermic, shallow Petrocalcic Calciustolls

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

A1--0 to 6 inches; dark grayish brown (10YR 4/2) very gravelly clay loam, very dark grayish brown (10YR 3/2) moist; weak medium subangular blocky structure parting to moderate very fine and fine granular; slightly hard, very friable; many very fine and fine and common medium and coarse roots throughout; common very fine and fine interstitial and tubular pores; about 55 percent by volume coarse fragments of which 25 percent are very pale brown (10YR 8/2) limestone pebbles and about 30 percent are very pale brown (10YR 8/4) caliche pebbles; strongly effervescent; slightly alkaline; clear wavy boundary.

A2--6 to 15 inches; dark gray (10YR 4/1) extremely stony clay loam, very dark gray (10YR 3/1) moist; weak medium subangular blocky structure parting to moderate very fine granular; slightly hard, very friable; common very fine to very coarse roots matted around stones; common very fine and fine interstitial and tubular pores; about 70 percent by volume caliche fragmants of which 10 percent pebbles, 35 percent cobbles and 25 percent stones; caliche fragments are very pale brown (10YR 8/2), have laminations on upper and lower surfaces, and are more etched and pitted on the lower surface; strongly effervescent; moderately alkaline; abrupt wavy boundary. (combined thickness of A horizon is 4 to 20 inches)

Bkm--15 to 20 inches; 85 percent white (10YR 8/1) and 10 percent reddish yellow (7.5YR 7/6) and 5 percent brown (10YR 5/3) indurated calcium carbonate; massive; few thin laminae streaks of very pale brown (10YR 8/4), very pale brown (10YR 7/4) moist; few embedded limestone fragments; brown (10YR 5/3) laminar cap 12 millimeters thick occurs at upper surface; strongly effervescent; moderately alkaline; abrupt wavy boundary. (4 to 20 inches thick)

Bkm2--20 to 32 inches; very pale brown (10YR 8/2) moderately cemented calcium carbonate; massive; violently effervescent; moderately alkaline; clear wavy boundary. (4 to 30 inches thick)

Bkm3--32 to 80 inches; 65 percent very pale brown (10YR 8/2) and 35 percent pink (7.5YR 7/3) cemented calcium carbonate that is 55 percent weakly cemented and crushes to very gravelly sandy loam texture, and 45 percent moderately cemented; massive; about 2 percent by volume limestone pebbles and 1 percent by volume chert pebbles; violently effervescent; moderately alkaline.

TYPE LOCATION: Edwards County, Texas. From the intersection of U.S. Highway 277 and Texas Highway 55 in northwestern Edwards County, 6.4 miles south on U.S. Highway 277 to entrance of Earwood Ranch, 1.75 miles east and south on ranch road, 56 feet southeast from centerline of road in rangeland. (Latitude 30 degrees, 11 minutes, 28 seconds north and Longitude 100 degrees, 39 minutes, and 36 seconds west)

RANGE IN CHARACTERISTICS: Depth to cemented caliche ranges from 4 to 20 inches. Rock fragments cover 5 to 75 percent of the surface.

The A horizon has hue of 7.5YR or 10YR, value of 3 to 5, and chroma of 1 to 3. Caliche and limestone fragments range from 35 to 85 percent by volume. Some pedons contain a few chert fragments. The fragments are dominantly pebbles and cobbles. Fragments larger than 10 inches comprise less than 35 percent by volume. The fine-earth fraction is loam, clay loam, or silty clay loam. Total clay ranges from 25 to 40 percent silicate clay ranges from 20 to 35 percent. Soil reaction is slightly alkaline or moderately alkaline.

The Bkm1 horizon is a strongly cemented or indurated petrocalcic horizon.

The Bkm2 and Bkm3 horizons are extremely weakly to moderately cemented pedtrocalci horizons. Rock fragments of limestone, caliche, and chert fragments are 2 to 90 percent by volume. A BCk horizon, where present, is noncemented caliche.

COMPETING SERIES: These include the Eola series in the same family, and the Cho.html">Boracho, Cho, Espy, Kavett, Kimbrough, Olmos, Pitzer, Queeny and Upton series in similar families. Eola soils formed in residuum weathered from Cretaceous marl beds. They are on uplands and have a Cr horizon below the petrocalcic horizon. Kavett soils are underlain by limestone bedrock within 20 inches. Cho, Espy, Kimbrough and Pitzer soils contain less than 35 percent rock fragments. Boracho, Espy, Kimbrough, Pitzer and Queeny soils contain less than 40 percent calcium carbonate equivalent. Olmos soils have mean annual soil temperature higher than 72 degrees F.

GEOGRAPHIC SETTING: Mailtrail soils are on gently sloping to moderately sloping high terraces and fans. Slopes are convex and gradients are dominantly 2 to 5 percent but range from 1 to 8 percent. The soil formed in calcareous, gravelly, loamy Pleistocene alluvium derived from areas of Cretaceous limestone, chalk, and marl. The climate is dry subhumid to semiarid. Average annual precipitation ranges from 16 to 26 inches, and annual P-E index ranges from 25 to about 39. The mean annual temperature ranges from 65 to 69 degrees F. Frost-free days range from 210 to 240. Elevation ranges from 1500 to 2500 feet.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Cho and Eola series and the Eckrant, Ector, Oplin, Real and Rio Diablo series. Cho soils are on similar landscapes. Rio Diablo soils are in valleys or on broad alluvial plains, are very deep, more clayey, contain less than 15 percent rock fragments, and do not have a calcic horizon. Eckrant soils are underlain by limestone bedrock within 20 inches, have more than 35 percent rock fragments, and do not have a calcic horizon. Eckrant, Ector, Eola, Oplin and Real soils are on uplands above the Pleistocene terraces on which Mailtrail soils occur.

DRAINAGE AND PERMEABILITY: The soils are well drained. Runoff is very low on 1 to 3 percent slopes, low on 3 to 5 percent slopes and medium on 5 to 8 percent slopes. Permeability is moderate above the petrocalcic, very slow permeability in the petrocalcic and moderately slow below the petrocalcic.

USE AND VEGETATION: Used as rangeland and is a source of caliche for roadbed construction. The native vegetation consists of short and mid grasses, woody plants and forbs. Live oak, redberry and blueberry juniper, are the dominant woody plants. Other woody plants are mesquite, agarito, persimmon, and prickly pear. Grasses are red grama, hairy tridens, fall witchgrass, Texas wintergrass, little bluestem, and three-awn. Important forbs are verbena, dogweed, croton, and orange zexmania.

DISTRIBUTION AND EXTENT: Western and Central Edwards Plateau of Texas. The series is moderately extensive.


SERIES ESTABLISHED: Edwards and Real Counties, Texas; 2000. The name is from Mailtrail Creek in western Edwards County.

REMARKS: These soils were previously included in the Olmos and Kimbrough series.

Diagnostic horizons and features recognized in this pedon are:

Mollic epipedon - 0 to 15 inches (A horizon).

Petrocalcic horizon - 15 to 80 inches (Bkm horizons).

Skeletal feature - more than 35 percent by volume of coarse fragments above the petrocalcic horizon.

ADDITIONAL DATA: Lab data is available from Texas Agricultural Extension Service, Soil Characterization Lab for the type location (S91TX-137-001).

National Cooperative Soil Survey