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 ( http://fermi.jhuapl.edu/states/states.html
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
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.
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),
(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
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.
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
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.,