The U.S. Geological Survey started creating topographic maps in 1884. They don’t even know how many maps they’ve produced since then but they’re estimating it at 200,000. It’s such a fascinating endeavor and they’ve written papers on its history. Their National Geospatial Program is scanning all of the old topographic maps into electronic format and making them available for free download. 90,000 are available already. You can also order a reasonably priced print, the same paper format many of us are familiar with for modern USGS topographic maps (available at stores that cater to hikers like REI). The maps are in GeoPDF format, viewable in Adobe Reader and you get even more functionality with the TerraGo Toolbar extension. I downloaded Mount St Helens from 1919. Yup, it’s a lot different now. And back then the maps were all done by people hiking around taking measurements. (Here’s more geeky detail on Mount St Helens topography if you’re interested.)