CENTRAL TEXAS UPLIFT
The domed rocks of the Central Texas Uplift form a topography different from that of the Black Hills. Erosion of a broad, uplifted dome here has exposed a core of old granites, gneisses, and schists, as in the Black Hills, but in the Central Texas Uplift, erosion has produced a topographic basin, rather than high peaks and spires, on the old rocks of the central area. A low plateau surface dissected into rounded ridges and narrow valleys slopes gently eastward from the edge of the central area to an escarpment at the Balcones fault zone, which determines the eastern edge of the Great Plains here. Northwest of the central basin the Colorado River flows in a broad lowland about 100 miles long, but the northern edge of the uplift, forming a divide between the Brazos and the Colorado Rivers, is a series of mesas formed of more resistant sandstone and limestone.
The cutting action of streams, modified or controlled in part by differences in hardness of the rock layers, has been responsible for the landforms of the Central Texas Uplift. Weathering of the old core rocks has softened them sufficiently to permit deeper erosion of the central area, and solution of limestone by ground water has formed such features as Longhorn Caverns, 11 miles southwest of Burnet, Tex.