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The Gulf Coastal Plain Region


The Gulf Coastal Plain. The Texas Gulf Coastal Plain is the westward extension of the Atlantic and Gulf Coastal Plain of the eastern and southern United States. As the name implies, the region is a plain which gradually rises as one moves inland away from the Gulf of Mexico. At the inner margin of the Plain, elevations approach 600-700 feet on average. The underlying rocks are sedimentary in nature, and they generally slope toward the Gulf, an indicator of their recent (in geological time) addition to the state. A number of authors note that the Texas Gulf Coastal Plain is actually a "belted" coastal plain in that it possesses a number of inward facing cuestas with long sloping backsides toward the Gulf. Those familiar with Huntsville may have taken note of the cuesta south of town (Shepard Hill). Others, more familiar with the terrain north of Huntsville will no doubt recognize the cuesta in the area of Buffalo.
The terrain and vegetative differences are such that even the most casual observer will readily recognize differences across the eastern and southern portions of the state that is the Gulf Coastal Plain. For our purposes, we will divide this region into five areas: the Gulf Coastal Prairies, the Pine Woods Belt, the Post Oak Belt, the Blackland Prairie and the South Texas Plain. A brief description of each follows. You are encouraged to familiarize yourself with each of these sub-regions as they are a critical component of this first section of the course. To assist you in your efforts, you should make liberal use of the applets and Study Aids provided.


Gulf Coastal Prairies. The Gulf Coastal Prairies region is located along the Texas coast between the Sabine River and Corpus Christi. The area is bounded on the northeast by the Pine Woods Belt, inland by the Post Oak Belt and in the southwest by the South Texas Plain. While the boundaries between the Pine Woods and the Post Oak belts are rather well defined, the region tends to merge somewhat imperceptably into the South Texas Plain. Behind the barrier islands and inland, the land is flat and generally grass-covered. Here the soils, while tending toward clay, are fertile. As one approaches the inland boundary, elevations increase to approximately 400 feet and the land becomes more undulating, and the soils sandier. While better drained than those nearer the coast, these soils tend to be less fertile. Most of the region is grass covered in the natural state. Near the coast, salt and marsh grasses with some low bushes predominate. Oaks and pecan become more prevalent inland, especially in the bottomlands, with pines occasionally found on the higher sites. While grasses are the dominant vegetation, it is important to note that as the rainfall decreases toward the southwest, the tall grasses of the eastern portions of the area give way to shorter varieties. Major streams include the Sabine, Trinity, Brazos and Colorado. See also The Handbook of Texas.


Pine Woods Belt. Bounded on the west by the Post Oak Belt and the south by the Gulf Coastal Prairies, the Pine Woods Belt is classic East Texas. As the name suggests, pines are the predominant vegetative type typically being found in most upland areas. The pine thrives in the warm, humid climate of the region where rainfalls typically exceed 40 to 50 inches. In fact, it is the relative lack of rainfall to the west that causes the pines to give way to the hardier oaks of the Post Oak Belt. Most of the land across the region would be classed as gently rolling, although near the southern margin the terrain is low and relatively flat while inland near Palestine relief can reach 200-300 feet and the general elevation exceed 600 feet. The soils across most of the region tend to be sandy, although the "redlands" near San Augustine have been well known for their relative fertility. The major streams are the Red, Sabine and Trinity. See also The Handbook of Texas.


Post Oak Belt. To the west of the Pine Woods Belt and inland from the Gulf Coastal Prairie lies the northeast to southwest-trending Post Oak Belt. Some 400 miles long and generally between 50 and 75 miles wide, the region, as the name implies, is dominated by a variety of oaks -- predominantly the somewhat scrubby post oak, as you might suspect. Pines are occasionally found (for instance around Bastrop) and cedar becomes more extensive as one approaches the southern boundary. Extending from the Red River in the north to the outskirts of San Antonio, most of the area lies at an elevation between 200 and 700 feet. The terrain is characterized as level to very gently rolling. The soils tend to be sandy and are generally not as fertile as those in surrounding regions; however, along the larger streams, such as the Brazos River, the land can be outstanding for agriculture. See also The Handbook of Texas.

Blackland Prairie. The Blackland Prairies, sometimes referred to as the "heart of Texas," extend from just south of the Red River south to San Antonio. For most of its length, it is bounded on the east by the Post Oak Belt. To the north and west is the Eastern Cross Timbers, the Grand Prairie, and to the south, the Edwards Plateau/Balcones Escarpment. Dallas, Waco, Austin and San Antonio are all found on the western margins of the Blackland Prairie. Most of the region is underlain by white chalk/limestone material which tends to weather into a thin, black, sticky-when-wet, extremely mineral-rich and fertile soil. While a veritable gumbo when wet, when dry the soils become very hard and can develop cracks that often exceed a foot or more in depth. The terrain tends to be level to very gently rolling. Most of the region lies between 400 and 600 feet elevation. While a number of large streams cross the Blackland, small streams are not common as there are few springs to be found in the area. See also The Handbook of Texas.

The South Texas Plains. The South Texas Plains are located in the extreme southern portion of the state. The boundary is formed in the north between Del Rio and San Antonio by the Balcones Escarpment. The Escarpment, some 1,000 feet high at Del Rio drops in elevation as one moves eastward. At San Antonio, the Escarpment stands some 300 feet above the Blackland Prairie. At San Antonio, the eastern boundary of the region then swings south striking the coast south of Corpus Christi. Much of this boundary is formed by the southern boundaries of the Blackland Prairie, Post Oak Belt and Gulf Coastal Prairies. Behind the barrier islands, the most notable of which is Padre Island, the land is generally flat and grass covered but becomes more rolling and brush-covered as one moves inland. Over most of the sparsely vegetated region, short grasses, mesquite, scrub oak and a variety of bushes predominate. The primary streams are the Rio Grande, which forms the border with Mexico, and the Nueces. Protected by the Edwards Plateau and the prevailing wind patterns from most cold winter storms, the region is characterized by southerly winds and bright, sunny, warm and dry weather much of the year. See also The Handbook of Texas.
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