The U.S. Geological Survey's National Geologic Map Database (NGMDB) offers a growing database of national geoscience information resources. The catalog, searchable by geographic area, keyword, author, map number and theme, includes over 90,000 records from 600 different publishers. This database is developing as a collaborative effort, primarily involving the USGS and the Association of American State Geologists (AASG). Mapping content contributed to the archives of the NGMDB follow the methods and standards being developed in accordance wtih the Geologic Mapping Act of 1992.
The website allows you to view and download thousands of different geologic maps using either text search or an intuitive map interface.