Upon further inspection I have an update. After reading the 5-7 mile distance from the Caspian Sea comment (Thanks) I closely inspected the Caspian sea and its surrounding highlands. I have been able to rule out all the previous options, but have reconsidered the Elburz Mountains, Shah Jahan Mountains, and The Caucasus Mountains. The likeliest being the Elburz. In reference to evidence of it being in South America, I declare it void due to direct reference to short distance from the Caspian Sea. Thank you again to the person who mentioned this in the comments.

This is a good theory, upon thinking on this thought I have come to a conclusion, if this spreads like any other disease then the higher concentration of people the better/faster it will spread. In such case we can look for regions that are not only completely infected but with varient versions and infected quickly, helping us narrow it down. Further more with our knowledge of the Topography of the Last City's location we can place it in a cyclonic or polar climate. Lastly we can use previous theories of where it may be as there was the evidence there still stands. Using this information as a filter we can bring it down to three places, The Ural Mountains, The Rocky Mountains, and The Kolyma Range. Those who can connect any of these places to lore or further narrow it down with evidence I may have missed.

Real time being not the Earth in destiny as gaurdians won't be in high enough concentration to be spread as far as the U.S. as the last city is nowhere in the Western Hemisphere to have almost the entire world lit up The colors represent which plague is in which area so American players are more likely to have one whereas European players another

Seems possible, looks like the map will finish in a couple of hours, so we SHOULD know the answer soon.