I recently installed Dynmap, and viewing the map I noticed this 1-chunk wide strip extending directly south from spawn for about 16000 blocks. It can't have been generated by a player, otherwise it would be much wider than one chunk.
I don't have any plugins installed that would have generated this (I don't think?); I have done some manual world editing to merge two worlds together (using a custom, Prismarine-based tool), but that can't have generated anything.
Why would this have generated?