I might not be the first one to bring this up but didn't we learn that Europe is possibly compromised from the TiVo in
chapter 3. Riots or something like that. As we learned most of the world is compermised. It leaves Canada, South America, Australia, Africa and Russia that we don't know the status of. Multiple hotspots is interesting. It seems to be only big metropolitan areas that are hotspots. Particularly seaside ones. So the leaked gas theory seems a little far fetched now. Giant squids (aka Cthluthlu) therory could still work as only seaborn major cites have been fully confirmed. Virus therory is still viable. Too many variables still to have a source not to mention another season. As a previous post stated
the colony has not been mentioned by the military. This chapter. My personal prediction at this point is
Fort Irwin is attacked and damaged or destroyed so
the tower group can escape ala the colony. This then would force the tower survivors to go back to LA to scavenge for food and other supplies.