So the tunneling is under Missou andsouthern Illinois now. Soon it will be completed coast to coast, well, at least coast to Denver and New Mexico and Utrah where the underground bunkers are being stocked.
No more “mine shaft gap?”
Haha!!
Really though...so much of Southern Illinois was subject to underground coal mining many years back that there is no telling what is going on down there. If a support column “pops” it would stress another one...then...pop.
We lost our Jr. High to mine sinkage when I was a kid...there was always the occasional “sink hole” closing a road.