In Cheyenne, Wyoming the characters take refuge in a military bunker. The title of the branch of service indicates USAAF, but it would only be listed as USAF. The airman in charge of the bunker is wearing a U.S. Marines uniform instead of the proper uniform worn by USAF airmen.
Many of the shots of things happening in the USA were actually from the Phillipines, Indonesia, Sumatra, etc. In particular, during the "ash is falling" news report, one shot shows the "Manila's Market Place" cinema, named on its own marquee.
While Rick is at a shelter in Denver, there is a shot of 2 chaplains. Their shoulder patches identify them as from San Bernardino County, California. No doubt with the difficulty in travel, they would have stayed in their own area and not travel 1,000 miles into the disaster.