Illinois Geologic Quadrangle (IGQ) - Illinois State Geological Survey

The IGQ series includes geologic and other maps depicted on U.S. Geological Survey 7.5-minute, 1:24,000-scale Topographic Quadrangle base maps. Geologic map themes include surficial geology, bedrock geology, drift thickness and other isopachous maps, bedrock topography and other structure contour surfaces, and others. The series also includes map themes such as landscape topography (e.g., hillshaded relief maps derived from digital elevation models), geochemical trends, hydrogeologic attributes, aquifer sensitivity, and distribution of data. They may include stratigraphic legends, brief descriptive text or longer associated reports, geologic cross sections or models, and illustrative diagrams and tables. IGQ maps are peer reviewed and conform to ISGS standards at the time of public release. This series was begun in 1986, initially using sequential numbers to identify the map (e.g., IGQ 1, IGQ 2, etc.). Currently, editions are identified by the quadrangle name and abbreviation for the type of geology described, for example, IGQ Naperville-BT for a bedrock topography map of the Naperville Quadrangle. Between 2004 and 2008, many of the maps in this series were originally published in the Illinois Preliminary Geologic Quadrangle (IPGM) map series for rapid dissemination. Most IPGM maps had minimal internal review, and were then revised and improved for publication in the IGQ series. The first map in this series was published in 1986.

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