What does Alec deduce as he and Mark follow the path of the others in Chapter 29?

Alec is able to deduce that the three of them were being chased and Deedee’s footprints disappeared, meaning she was carried. They follow the path to a canyon, which Alec reveals to be the landing area for the Berg. Alec believes the canyon houses an old government bunker, because they are so close to Asheville.