LOCATION SANTO TOMAS NM+TX AZEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, thermic Pachic Haplustolls
TYPICAL PEDON: Santo Tomas very gravelly loam - rangeland. (Colors are for dry soil unless otherwise noted.)
A1--0 to 2 inches; brown (10YR 4/3) very gravelly loam, very dark brown (10YR 2/2) moist; weak thin platy and weak very fine granular structure between gravel; loose; common fine roots; 40 percent gravel; neutral; abrupt smooth boundary. (1 to 4 inches thick)
A2--2 to 10 inches; dark grayish brown (10YR 4/2) very gravelly loam, very dark brown (10YR 2/2) moist; weak very fine granular structure; slightly hard; common fine roots; 35 percent gravel and 10 percent cobble; neutral; clear smooth boundary. (6 to 20 inches thick)
A3--10 to 20 inches; dark grayish brown (10YR 4/2) very gravelly sandy loam, very dark brown (10YR 2/2) moist; moderate very fine granular structure; slightly hard; common fine roots; 30 percent gravel and 15 percent cobble; neutral; clear smooth boundary. (6 to 20 inches thick)
A4--20 to 30 inches; grayish brown (10YR 5/2) very gravelly sandy loam, very dark grayish brown (10YR 3/2) moist, moderate fine granular structure; slightly hard; few fine roots; few pockets of A3 horizon material an inch or two in diameter; 25 percent gravel and 10 percent stones; neutral; gradual wavy boundary. (7 to 20 inches thick)
C--30 to 65 inches; brown (7.5YR 5/4) very gravelly sandy loam, brown (7.5YR 4/4) moist; massive; soft and loose; few roots; 30 percent gravel, 5 percent cobble, and 10 percent stone; neutral; gradual boundary.
TYPE LOCATION: Dona Ana County, (Desert Soil-Geomorphology Project), New Mexico; just northeast of Soledad Canyon Road; northeast bank of arroyo; in the NE1/4, SE1/4 of section 13, T.23 S., R.3 E.; 106 degrees, 35 minutes, 14 seconds - west longitude; 32 degrees, 18 minutes, 18 seconds - north latitude.
RANGE IN CHARACTERISTICS:
Soil moisture - Intermittently moist in some part of the soil moisture control section during December - April and July - September. Driest during May and June. Ustic aridic soil moisture regime.
Soil Temperature - 60 to 68 degrees F.
Rock fragments - 20 to 45 percent gravel, 10 to 20 percent cobble and 5 to 10 percent stone
Reaction - neutral to slightly alkaline, typically noneffervescent to depths of many feet but at least to 70 inches
Organic matter: greater than 1.0 percent in the upper 20 inches; decreasing regularly with depth
A horizon
Hue: 5YR, 10YR
Value: 3 through 5 dry, 1 through 3 moist
Chroma: 1 through 3, dry or moist
C horizon
Hue: 7.5YR, 7.5YR
Value: 4 or 5 dry, 3 or 4 moist
Chroma: 4 or 5, dry or moist
Texture: very gravelly sandy loam, very gravelly fine sandy loam
Some pedons have a buried soil below 40 inches.
COMPETING SERIES: These are the
Enash (NM) and
Sanmoss (TX) series. Enash and Sanmoss soils are in the Aridic ustic moisture regime.
Sanmoss soils depth to effervescent and lime accumulation range from 12 to 40 inches. The Bk horizon contains less than 5 percent calcium carbonates equivalent.
GEOGRAPHIC SETTING: Santo Tomas soils occur along mountain fronts on alluvial fans and terraces of Holocene age. Slopes are usually 5 to 10 percent and range from 1 to 15 percent. The soils formed in very gravelly sediments derived from rocks such as rhyolite and andesite. The mean annual air temperature ranges from about 58 percent to 66 percent F. Mean annual precipitation is about 10 to 16 inches with a marked summer maximum. Elevations range from 3,800 to 6,000. The frost-free period is 160 to 200 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Aladdin, Boracho, Caralampi, Hawkeye, Nolan, Pinaleno and Terino series. Caralampi, Pinaleno, Nolan and Terino soils have argillic horizons and do not have mollic epipedons. Boracho soils have petrocalcic horizons. Aladdin and Hawkeye soils are not skeletal.
DRAINAGE AND PERMEABILITY: Well-drained; medium runoff; moderate permeability.
USE AND VEGETATION: Used for livestock grazing and wildlife habitat. Vegetation includes snakeweed, fluffgrass, mesquite, cholla, prickly pear, in places, scattered clumps of black grama and blue grama.
DISTRIBUTION AND EXTENT: Southern New Mexico, Southeastern Arizonan and west Texas. Santo Tomas soils are of moderate extent. MLRAs 41 & 42.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Phoenix, Arizona
SERIES ESTABLISHED: Desert Soil-Geomorphology Project; Dona Ana County, New Mexico; 1971.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - The zone from 0 to 30 inches (A1, A2, A3, A4 horizons)
Pachic feature - The over thickened mollic epipedon with regular decreasing organic matter (16 to 30 inches)
The competing series section was updated to recognized Sanmoss and Enash series. These soils classify as pachic but they are series mapped in the Aridic ustic moisture regime.
This series represents an identified soil within the Desert Soil-Geomorphology Project, Las Cruces, New Mexico. The project was a study of soils and geomorphology in an arid and semi-arid environment. The series is extensively referenced in many documents, publications and thesis. Revision outside the project area is discouraged in order to preserve the historical concept for research.
ADDITIONAL DATA: Data from pedon S60NMex-7-12 (L.H. Gile and R.B. Grossman. 1979. The Desert Project Soil Monograph. Document PB80-135304. National Technical Information Service., Springfield, VA.). The typifying pedon is the sampled pedon.