The Colorado River Industrial Development Association area consists of ten counties [Bastrop, Blanco, Burnet, Colorado, Fayette, Llano, Matagorda, San Saba, Travis, and Wharton counties] in the lower watershed of Colorado River in Texas. The rocks exposed in the upriver part of the area include Precambrian metamorphic and igneous rocks and Paleozoic and Lower Cretaceous sedimentary rocks. In the Austin region Upper Cretaceous sedimentary rocks are exposed. In the downstream part of the area the rocks are of Tertiary and Quaternary ages. The principal mineral resource materials are industrial rocks and minerals. In the part of the area from Austin upstream, the most important materials are building stone, chemical limestone and dolomite, cement materials, graphite, soapstone, serpentine, vermiculite, and iron ore. From Austin downstream, the most important materials are sand and gravel, bleaching clay, burning clay, lignite, salt, sulfur, and oyster shell. There are small or low-grade deposits of many other materials, especially in the upriver region.