This polygon shapefile is a digital version of U.S. Geological Survey Open File Report 2004-1352, Engineering Aspects of Karst. The open-file report is a map with accompanying explanatory text that shows areas containing distinctive surficial and subterranean features developed by solution of carbonate and other rocks and characterized by closed depressions, sinking streams, and cavern openings. These areas are commonly referred to as karst. Included on the map are areas of features analogous to karst also called pseudokarst, which is karst-like terrain produced by processes other than the dissolution of rocks. Also included are lines indicating areas in which extensive historical subsidence has occurred. When used in its broadest sense, the term karst encompasses many surface and subsurface conditions that give rise to problems in engineering geology. Most of these problems pertain to subterranean features that affect foundations, tunnels, reservoir tightness, and diversion of surface drainage. Subterranean openings may be the habitat of unique and, in some cases, endangered fauna. This layer is part of the 1997-2014 edition of the National Atlas of the United States. These data are intended for geographic display and analysis at the national level, and for large regional areas. The data should be displayed and analyzed at scales appropriate for 1:7,500,000-scale data. No responsibility is assumed by the U.S. Geological Survey in the use of these data. This layer is presented in the WGS84 coordinate system for web display purposes. Downloadable data are provided in native coordinate system or projection.