Reply #2: I was just reading about this

[htuttle]

I was surprised when I recently heard about it, since it's less than 50 miles from here.

The theory I found most interesting is that they had something to do with 'Copper Age'/pre-Bronze Age copper mines. The theory goes on that it was the legends of these ancient copper mines that brought Mississipian/Mound-Builder culture up here to build their own copper mines, the remains of which are connected to the nearby Aztalan site.