* The Gulf Coastal Plain is ringed by the barrier islands and lagoons of the Texas coastline, as at the San Padre Island National Seashore and Aransas National Wildlife Refuge. This huge region ranges from the fertile valley of the lower Rio Grande and the brush country of South Texas, across sand plains laced by streams fringed with subtropical hardwoods, over rich blackland prairies and post-oak woods, to the pineywoods, salt domes, and bayous of East Texas, as seen in the Big Thicket National Preserve and Caddo Lake State Park.
* The Rolling Plains sweep from the post-oak woods of Western Cross Timbers across the reddish prairies that roll northward from cuesta to cuesta into the eastern Panhandle, where they butt against the High Plains escarpment, whose Ogallala caprock is deeply notched by the headwaters of major rivers, as in Palo Duro Canyon State Park.
* The flatness of the High Plains is relieved by playas, dune fields, and a wide band of solution valleys, the Canadian Breaks, which slashes through the caprock of the northern Panhandle.
* The Hill Country encompasses the canyon-riddled fault escarpment of the Edwards Plateau, the flower-festooned and sinkhole-pocked limestone plateau, and the Llano Uplift studded with ancient granite domes, as in the Enchanted Rock State Natural Area.
* In the Basin and Range west of the Pecos, jagged spurs of the Rockies, such as the Chisos, Guadalupe, and Davis mountains, alternate with flat basins dotted with creosote and agave. Along the western border of the Trans-Pecos region, the upper Rio Grande and its tributaries cut mountain gorges, such as the Santa Elena Canyon in Big Bend National Park.
