USGS Historical Topographic Map Explorer

Here is a great site if you wish to explore topographical maps for the areas in the US where your ancestors lived.

The interface is easy to use. Zoom to the area of the US you are interested in (this is done by using your mouse scroll wheel), then where ever you click, a timeline of maps available will appear at the bottom of the screen. The year of publication of the map and the scale will be shown. Click on the map of interest and it will be displayed. In the left panel of the screen you’ll find a handy set of instructions to guide you.

Once the map is displayed, you can zoom in without loss of detail. You can download your chosen map to a PDF file.

USGS Historical Topographic Map Explorer