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The Great Plains Region

The Great Plains. As was the case with both the Coastal Plains and the North Central Lowlands, the Great Plains of Texas are the southern extension of a much larger physiographic region of the United States and Canada. This elevated, flat surfaced region slopes gradually eastward from the Rocky Mountains. In Texas, this region is divided into three distinct sub-regions:  the High Plains, the Edwards Plateau and the Llano Basin. 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.
The High Plains.  In Texas the High Plains, sometimes called the Staked Plains, the Llano Estacado or the Panhandle Plains, make up much of what we know as the "Panhandle." Bounded on the north and east by Oklahoma and New Mexico respectively, the High Plains region is a high almost level plain which rises gradually (at a rate of about 10 feet per mile) toward the west/northwest. To the east, the boundary with the Lower Plains is defined by the Caprock Escarpment. Here the land rises abruptly, depending upon where you are, from 200 to 300 feet to as much as 1,000 feet. Toward the south where the High Plains meet the Edwards Plateau, the boundary is much less obvious. Although flat, much of the High Plains in Texas lie between 2,700 and 4,500 feet. Here are found the headwaters of the Red, Canadian, Brazos and Colorado rivers. Most of these streams flow in deeply incised canyons cut into the otherwise almost level surface. The native vegetation is typically short grass with trees usually only found along area watercourses. See also The Handbook of Texas.

The Edwards Plateau.  The Edwards Plateau, the eastern portions often referred to as the "Hill Country," is the southern-most extension of the Great Plains in Texas. In the east, the Plateau consists of rocky, steep-sided slopes, clear spring-fed streams and a surface covered with scrub oak, cedar, grasses and brush. To the west, where rainfall is much reduced, the Plateau (called the Stockton Plateau) takes on more the appearance of a plain and the vegetative cover tends more to short grass and brush. The southern and eastern boundaries are marked by the presence of the Balcones Escarpment, the result of faulting which has uplifted the Plateau some 600 or so feet above the surrounding South Texas Plain (to the south) and Blackland Prairies (to the east). The underlying rock is limestone which typically weathers into a thin, black soil. Over much of the area, because the soil is eroded almost as quickly as it is formed, the underlying rock lies exposed. Cracks and fissures in the limestone create conditions conducive to the absorption of large quantities of water underground. This water comes to the surface via faults in a series of springs especially along the Balcones Escarpment -- Barton, Comal and San Marcos springs being among the larger. In addition, a number of significant caves and other karst features are to be found in the area. Among the better known are Inner Space Cavern at Georgetown, Longhorn Cavern at Burnet, Natural Bridge Caverns at New Braunfels and Wonder Cave at San Marcos. See also The Handbook of Texas.
The Llano Basin.  The Llano Basin is located near the confluence of the Colorado and Llano rivers in Central Texas. Though called a basin, the region is actually a dome/uplift. Originally covered with a veneer of sedimentary rock, time and the elements have stripped away this softer rock to reveal a granite intrusion (Enchanted Rock being the most famous part of this formation). The overlying sedimentary rocks now form a series of in-facing escarpments. As you might expect, soils over this hard granitic material are thin and relatively unproductive for crop agriculture. That said, the relative abundance of water in the area, much of it derived from springs, gives the area a less forbidding appearance than the surrounding uplands. See also The Handbook of Texas.

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