SCSB# 395
MLRA 42: Southern Desertic Basins, Mountains, and Plains
R.E. Zartman and B.L. Allen
Texas Tech University

Chapter Contents

Major land resource area (MLRA) 42 comprises 31.7 million acres and extends from Texas northwest to include portions of Arizona and New Mexico. This document will be restricted to areas of Texas, which encompass approximately 19 million acres. Much of the area does not have second- or third-order soil surveys. This portion of the Chihuahuan desert has a very low agricultural productivity without irrigation. Only limited areas are irrigated for cotton, vegetables, and forage crops. Most of the area is rangeland, either desert grassland or desert shrub. Productivity is measured in animals per section rather than animals per acre basis.

Elevation and Topography
The elevation ranges from 800 m in the basins and valleys to more than 2600 m in the mountains. Topography ranges from steep mountain slopes to gently sloping alluvial fans and nearly flat basin floors. The topography is mostly determined by the steep mountain slopes and resulting fans. High terraces are preserved only in some places along the Rio GrandeRiver. Significant flood plains are present only along the Rio Grande and the Pecos Rivers. A shaded relief map for this MLRA may be accessed through the internet at ( )

The soils of this MLRA are in the aridic moisture and thermic temperature regimes. The range in precipitation is from 200 to 325 mm but varies widely from year to year. Precipitation events generally occur in the late summer with strong thunderstorms prevailing. Snow, while infrequent, is not unprecedented. Mean minimum January temperatures range from 26 to 36o F while the mean maximum January temperatures range from 52 to 64o F. Mean minimum July temperatures range from 60 to 70o F. while mean maximum July temperatures range from 82 to 100 o F. Minimum and maximum temperatures arein the mountains and basins, respectively.

The STATSGO soils map for this MLRA is provided in Fig. 1. Haplocalcids and Petrocalcids in mixed mineralogy and superactive cation exchange capacity (CEC) families are extensive in the area. Some are in carbonatic families. They have formed mostly in locally derived, often gravely, alluvium, many of the deposits have been subjected to wind reworking in various degrees. Shallow Haplocalcids over limestone with carbonatic mineralogy are also common. Haplocambids, form in both gravely and non-gravely alluvium or in eolian sandy minerals. The gravely sediments are on fans or associated in intermittent streams, often inset into the fans, which originate in the low mountain ranges. Morphology of the Haplocambids suggest a Holocene age. They also are mostly mixed in mineralogy and have superactive CEC families.

Calciargids, Petroargids, and Haplargids are moderately extensive in the area. The calcic horizon has formed in the lower part of the argillic horizon in many of the Calciargids, suggesting a recalcification of the horizon. The Argids have formed mostly in the fan alluvium, basin-fill deposits and sandy eolian deposits. They too are mostly in mixed mineralogy and superactive CEC classes.

Fig. 1. STATSGO soils of the Southern Desertic Basins, Mountains, and Plains MLRA 42.

Haplogypsids are also locally important in the area. They have formed in ancient loamy sediments which occupy broad valleys. Also, less extensive occurrences are in coarser eolian sediments. Others may be present over primary gypsum (Castile Formation). A gypsic horizon may or may not be present in such soils.

Torriorthents developed over hard and soft bedrock, gravely fan and stream alluvium and volcanic tuff are extensive in the area. Torripsamments, developed in eolian sediments, are moderately extensive. The most extensive areas of Torrifluvents are on former flood plains of the Rio Grande and the Pecos River. These highly productive loamy and clayey soils no longer flood because of levees and upstream dams. More gravely Torrifluvents are in materials deposited by smaller ephemeral tributaries of the larger streams and also by those on the fans.

Torrerts are developed in very clayey basin-fill sediments. They also occur to a limited extent in deposits associated with extant streams.

While the soils of this MLRA are large in areal extent, their agricultural use is limited due to low precipitation (Buol, 1973). Soils by great group within orders for this MLRA are presented alphabetically in Table 1. Selected soil physical properties of MLRA 42 which have an areal extent of 10,000 acres or more are presented in Table 2. We are greatly indebted to Mr. W. M. Risinger of the USDA-NRCS for help in editing these tables.

Data we have for those major soils (>10,000 acres) listed above are limited to the Holloman (Jaynes, 1977; Sexton, 1975), Lozier (Wilkey, 1979), Orla (Sexton, 1975; Challa, 1987), Reeves (Jaynes, 1977; Sexton, 1975), Upton (Sexton, 1975), Verhalen (Casby-Horton, 1997), and Wink (Sexton, 1975).

We have specific information on the physical and chemical properties of the soils associated with the profiles specified above. The detailed information associated with the Organic Carbon, pH, Calcium Carbonate, and Gypsum are presented in Table 3. Electrical conductivity and soluble cation data for these soils are presented in Table 4. Soil water data that are available are presented in Table 5. Particle size distributions are presented in Table 6.

The soils of MLRA 42 occur within the most arid climate in the southern region of the United States. While portions of the region are irrigated by ground or surface water, most of the region is used as rangelands. Irrigation of row crops is a mixed blessing, with saline or sodic water a problem.

Literature Cited
Buol, S. W. (ed). 1973. Soils of the Southern States and Puerto Rico. Southern Cooperative Series Bulletin 174.

Casby-Horton, S. 1997. Soil and geological studies at Sierra Blanca, Texas. Ph. D. Diss. Texas Tech Univ., Lubbock.

Challa, A. 1987. Impact of irrigation on morphological, physiochemical, and mineralogical properties of soils in Trans-Pecos, Texas. M.S. Thesis. Texas Tech Univ., Lubbock, Texas.

Jaynes, D. C. 1977. Effects of gypsiferous soils on the distribution of cresotebush (Larrea tridentata [D.C.] Coville). M.S. Thesis. Texas Tech Univ., Lubbock.

Nkalai D. and R. E Zartman. 1985. A comparison of the unsaturated hydraulic conductivities of calcareous and non calcareous soils. Soil Science 140(3):179-183.

NRCS. 1996. Personal communications with W. Mike Risinger, Temple, Texas.

Sexton, W. T. 1975. The effect of salinity on cresotebush (Larrea tridentata [D.C.]) distribution in west Texas. M.S. Thesis. Texas Tech Univ., Lubbock.

Wilkey, J. S. 1979. Effects of aspects and elevation on soil properties in Guadalupe Mountains National Park, Texas. M.S. Thesis. Texas Tech Univ., Lubbock.

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