The Paleozoic rocks of central Texas occur in the numerous fault blocks that compose the Llano uplift, also known as the Central Mineral Region, a structural high in the Precambrian basement centered in Llano County, northwest of Austin (Fig. 1). The predominant trend of the fault blocks is southwest to northeast. For the most part, the Paleozoic rocks are preserved in grabens. Few fault blocks are large enough, however, to display the entire Paleozoic section; thus, no single transect can be made that will allow a view of the entire section. Rather, the Paleozoic section must be examined at a number of isolated localities from which a regional picture can then be formulated. Rapid facies changes in some of the formations compound the difficulty of piecing together a representative section. The Brownwood and Llano sheets of the Geologic Atlas of Texas (Barnes and others, 1976, 1981) cover the entire area of interest.
Most of the localities are along roadcuts where access presents no problem; possible restrictions on public access to locality 7 are noted. Because of access problems, no localities are presented for the thin, patchy Upper Ordovician, Silurian, and Devonian formations, few of which are in normal stratigraphic position. Most of these are preserved in collapse structures, sinks, and crack fillings.
Figures & Tables
One of six volumes generated by each GSA section for the Decade of North American Geology (DNAG) project, this Centennial Field Guide contains descriptions of 100 sites or site clusters representing outstanding geologic locations in Arkansas, Kansas, Oklahoma, and Texas.