Via Jason Kottke, here's a fascinating map from the ACLU:
(click to enlarge)
As the map itself notes, fully two-thirds of the U.S. population lives in this border zone, which was established by the Justice Department in 1953 without any public discussion or debate. And it's a real problem because Border Patrol agents have "certain extra-Constitutional powers" in this region, according to the ACLU, such as searching vehicles or luggage without a warrant or even a suspicion of wrongdoing.
Even if that's appropriate for an actual border crossing, it's another matter entirely when you're covering a gigantic swath of land where a majority of the country lives—especially when, as the ACLU says, the Border Patrol "frequently ignores" even the more limited constitutional protections afforded in the border areas.
You can learn more about the issue here, and take our poll: Do you live in the U.S. border zone?