If you want to know what geological maps exist or are in work anywhere in the U.S., there’s a new web-accessible database to provide the answer. The National Geological Map Database also indexes digital mapping and documents such as reports.
The interface to this web site allows searching through several methods. The simplest approach uses a series of linked reference maps. For instance, you can click on Wisconsin, then search for mapping done for standard 100:000-scale quadrangles.
You can also search by geographic feature (e.g., Lily Lake in Oconto County), then narrow the search to detailed maps of bedrock in paper form produced since 1980 or simply find all maps of all themes in all formats of all vintages.
The NGMD is a joint project of the U.S. Geological Survey’s National Cooperative Geological Mapping Program and the Association of American State Geologists. Note that this searchable index does not contain images of the maps; it is a hybrid of a card catalog and a spatial index of mapping. Surf over and take a look at http://ngmsvr.wr.usgs.gov/ngmdb/.