And to clarify the question at hand, what about the short, specific segments that have been over-built and replaced by a building or roadway.  These features require excavation and there generally is no trace through a large flat parking lot or through someone's bedroom.  Specifically, what if the only way to verify anything was ever there is to use a metal detector and ground penetrating radar?

Short of breaking out the high-tech, what is good enough to consider proof?  A suspicious discoloration of crops in farmland where the land is level and the field has been plowed?