Often they’re just located because the local folks had always been aware of them and someone heard about it. With orbital surveys more have been found, which is important in sparsely populated areas. Oh, and just call me Cap’t Obvious. 🎩
That’s right! I forgot the orbital surveys! I think there are folks whose hobby is to go through things like Google Earth looking for what might turn up in a remote place. I’ve done that once for looking at things like the Nazca Lines.