For states that are united, there sure are a lot of ways to break them down. Most, however, are nothing much to look at compared with how nature’s divisions sketch out…
Click on the map to find out what all those numbers mean on Wikipedia, or if you want to go straight to the source, the EPA’s Western Ecology Division has some beautiful pdfs available for download, including state-level maps.
Honorable mention goes to the World Wildlife Fund’s list of U.S. ecoregions. Always good to have a second source.
