Land use: Most of this area is cropland or improved pasture that is extensively irrigated, but large acreages are in range. Major crops are cotton, grain sorghum, citrus, onions, cabbage, and other truck crops. The range is mainly grazed by beef cattle and wildlife. Hunting leases for quail, white-winged dove, and mourning dove are an important source of income. Major land use problems are saline soils and inadequate subsurface drainage on cropland.
Elevation and topography: Elevation ranges from sea level in the east to about 200 m in the northwest, but is mainly less than 100 m. Much of the area is nearly level. Drainageways are shallow and have low gradients.
Climate: Average annual precipitation-425 to 700 mm. Maximum precipitation is during the growing season. Average annual temperature-22 to 23 C. Average freeze-free period-300 to 330 days.
Water: Rainfall is adequate for the growth of range grasses. It is low in the western and central parts of the area and marginal in the eastern. High temperatures and high evaporation and transpiration rates limit crop production. The Rio Grande, the only perennial stream, provides water for irrigation. Locally, deep wells and ponds provide water for live- stock, domestic use, and irrigation.
Soils: Most of the soils are Ustalfs. They are deep, moderately fine textured and fine textured soils that formed in alluvial sediments. They have a hyperthermic temperature regime, an ustic moisture regime, and mixed mineralogy. Ustolls having mixed mineralogy are also extensive. Nearly level to gently sloping Paleustalfs (Delfina and Nueces series) are on plains in the northeast. Nearly level to gently undulating Haplustalfs (Brennan, Duval, and Hebbronville series) are on plains in the west. Nearly level to gently sloping Calciustolls (Hidalgo and Raymondville series) are on plains in the central and eastern parts of the area. Nearly level Ustifluvents (Camargo, Rio Grande, and Zalla series) are on flood plains along the Rio Grande.
Potential natural vegetation: This area supports open mid grass prairie
vegetation with scattered woody plants and some perennial forbs and legumes
on upland soils. Twoflower and fourflower trichloris, plains bristlegrass,
and lovegrass tridens are among the dominant grasses. Desert yaupon, spiny
hackberry, and blackbrush are major woody plants. Tall and mid grasses such
as switchgrass, giant sacaton, fourflower trichloris, big sandbur, little
bluestem, and southwestern bristlegrass are dominant on the savanna plant
communities on bottom lands. Hackberry and elms are major woody plants. Forbs
are important but minor components of the plant communities.
(From "Land Resource Regions and Major Land Resource Areas of the United
States". United States Department of Agriculture Soil Conservation Service
Handbook 296. Dec. 1981. pages 58-59.)