They got flooded out and washed away when teh mile thick glaciers melted. IOW, Global Warming killed them all!..................................
Thanks RB for the other link, I found the extra graphics at this source irresistible. I’ve got the “Burnt City” keyword topics list on deck, but won’t post it to anyone, just in case.
Regarding your “Global Warming”/glacier flood theory. This civilization was reported as IV millennium BC, in which case these people would have been around 5 to 6,000 years ago. The glacial meltdown was long since over by perhaps another 5,000 years earlier or more. Of course you may have been joking, as the glaciers were never 10 miles thick.