[Bentsen-Rio Grande Valley State Park] [Laguna Atascosa National Wildlife Refuge] [Sabal Palm Audubon Society Sanctuary] [Santa Ana National Wildlife Refuge] [Rio Grande Valley National Wildlife Refuge]

General information about the lower Rio Grande Valley

The lower Rio Grande Valley, a flood plain in south Texas, includes Cameron, Hidalgo, Starr and Willacy counties. (The neighboring area south of the Rio Grande in the state of Tamaulipas, Mexico, is generally excluded, since the name of the river in Mexico is Rio Bravo del Norte.) The area is located within a semi-dry subtropic zone, characterized by mean annual temperature approximately 23°C (74°F), mean annual relative humidity 85-90% mornings, 50-70% evenings, mean annual precipitation 43-65mm (17-26in), mean annual evaporation 90-160mm (36-64in), mean annual sunshine 65-70%. Humidity and precipitation are highest near the coast (Arbingast et al. 1976).

Most of the area is topographically flat, except for portions of southeastern Starr County, which often is called the hill country of the Rio Grande Valley. The elevation is mostly below 75 meters. A small region in northern Starr County exceeds 150 meter (Arbingast et al. 1976). The soil consists of clays and loams of different types, with a higher percentage of large particle type loams in Starr county (U.S. Department of Agriculture Soil Conservation Service 1981). Throughout the Valley, but especially northern and western Hidalgo county and eastern Starr county, there are man-made gravel and caliche pits. In the hilly southeastern Starr County, many slopes have rock outcroppings, cliffs and large boulders.

The flora of the Valley falls within the Tamaulipan biotic province on the Gulf of Mexico coastal plain. Typical vegetation consists of thorny shrub (U.S. Fish and Wildlife Service 1985). Much of the area is heavily cultivated. Land not used for agriculture has often been grazed and trampled by cattle. Other areas have just been root-plowed to remove the original thorn forest vegetation (the brush). Large tracts are bare scraped, not used for anything, and without the brush binding the soil, exposed to water and wind erosion.

Some original habitats have been saved for the future. Areas protected include the areas listed on top of this page. In 1985 when I surveyed the scorpions of the area (Nilsson 1987) the U.S. Fish and Wildlife Service estimated that about 90% of the original habitat on the U.S. side of the river had been lost and that the remaining brushland in private ownership would be destroyed within five years. Today, anyone driving in southeastern Starr County towards Rio Grande City and Roma can see that the once beautiful area is being converted into