Together, all of these "quadrangle" maps create The National Map
The library has a super collection of topographic maps, particularly for Maryland, from the USGS. For the last few years, however, the primary source for these maps has been the US Topo website. Some of the Quadrangles have versions dating back to the 1800's, and so browsing these maps can provide an interesting tour through history!
If you are interested in diving a little deeper into the web site, the Government Printing Office has created a page with Tricks and Tips for Finding and Using USGS Topographic Maps. This site gives you additional information about advanced searching and features, such as the TerraGo Toolbar, which will allow you to mark up a map for activities such as hiking.
Every week, the Ort Library brings you a new and outstanding resource from the Web or from one of the library's databases. To get an archive of all FOR entries, click here. Also, you can suggest a website that provides well-organized access to useful info.