Tucson, Arizona is the second-largest city in Arizona. 2 years after the invasion, the 1st NIX were low on ammunition due to an engagement with an Espheni outpost. Two days after the engagement, the 1st NIX made their way to Davis-Monthan Air Force Base a military installation 5 kilometers outside Tucson to resupply their ammunition.
Cochise mentions that Tuscon, Arizona has one of the largest resistance groups.(Find your Warrior)