Quaternary geologic map of the Austin 4° x 6° quadrangle, United States

Abstract

NOTE: This map is the product of collaboration of the Texas Bureau of Economic Geology and the U.S. Geological Survey, and is designed for both scientific and practical purposes. It was prepared in two stages. First, the map and map explanations were prepared by the State compiler. Second, information on the map was integrated with that of adjacent maps, locally supplemented, and related to a uniform map symbol classification by the editors. Map unit descriptions were edited, supplemented, and coordinated with those of other maps of this series so that individual unit descriptions are applicable throughout both this map and all other maps of the series. Problems of mapping or interpretation in different areas were resolved by correspondence to the extent possible; most simply reflect differences in available information or differences in philosophies of mapping and serve to encourage further investigation. Less than forty percent of the surficial deposits of the United States have been mapped and described. Traditionally, mapping of surficial deposits has focused on glacial, alluvial, eolian, lacustrine, marine, and landslide deposits. Slope and upland deposits have been mapped in detail only in restricted areas. However, an enormous amount of engineering construction and many important problems of land use and land management are associated with regions that have extensive slope and upland deposits (colluvium and residuum, for example). These materials have many different physical characteristics. Therefore, an effort has been made to classify, map, and describe these deposits, based in large part on published and unpublished subsoil data, distribution and structure of bedrock parent materials, slope, and unpublished interpretations of individuals. The classification is crude, but represents a first step toward a more refined and useful product. For scientific purposes, the map differentiates Quaternary surficial deposits on the basis of a combination of criteria, such as lithology, texture, genesis, stratigraphic relationships, and age, as shown on the correlation diagram and indicated in the map unit descriptions. Some geomorphic features, such as relict beach ridges, are distinguished as map units. Erosional features, such as stream terraces, are not distinguished, and differentiation of alluvial deposits of different ages is possible at a scale of 1:1,000,000 only where they are extensive. For practical purposes, the map is a surficial materials map, on which materials are distinguished on the basis of texture, composition, and local specific characteristics such as swelling clay. It is not a map of pedologic or agronomic soils. Rather it is a generalized map of soils as recognized in engineering geology, or of subsoils or parent materials from which pedologic and agronomic soils are formed. As a materials map it serves as a base from which engineering, land-use-planning, or land-management maps can be derived.