Interesting theory SeanO.
I agree that the turning back was the issue and it was a returning to the condemned path of S & G. As to the earthquake thing, that is less likely. More likely was asteroid or falling space debris. The area is riddled with evaporates as you said and the story may have come from the life-like humanoid pillars of these salts.
It is just as likely, that upon turning back she was reduced to carbon by the falling fire…because she was too close to the condemned cities.
Earthquakes are plentiful in the area but I can’t see these evaporate rocks burning.
The story about looking back when told to go forward and the consequences is also brought up in the new testament about the man plowing the field who looks back, resulting in everything he is presently doing being uneven, thus unworthy.