-snip-
Neat. I'll see if I can make a map.
As for the apocalypse...hm...maybe some kind of self-replicating magical thingy? A ven Neuman golem, or mitosis-ing spirit?
We should also consider how the druidic totems protect from the apocalypse, and what the side effects would be. If they were meant to protect from the casual waste of civilization, they might well attempt to reverse it, meaning that artificial structures would need to be constantly replaced and cobblestone roads would be basically impossible in all but the wealthiest areas.
Oh, and I had an idea about Oasis. It has a bunch of druidic totems, but those were presumably erected before the city was built. I'm imagining something like the Aztec city of Tenochtitlan, which was conquered by Spain and then slowly turned into a Western city (I think it's Mexico City now?). Oasis could have once been the center of a local nation or organization of druids, which was then annexed by the local nation/nobles/church/whatever and turned into a proper city, albeit with a number of druids (who--along with the magic of the totems--stopped them from being torn down). This city became a popular tourist destination and a center of trade, and then the last bastion of civilization. (That we know of.)