If you think about it, you don't even need to send scouts to
Fort Irwin. If its as well prepared as
Michael said they should have a radio or some such. It would be easier if the survivors searched for some sort of radio gear at the National Guard station or heck just pick up a phone.
Angel or Michael should know of some general emergency military radio frequencies to contact them.
And if someone does answer they can even throw out some military lingo to feel out if it is military they are talking to or just some bad guys faking it, a la
Marcus.
Also if no one does answer they can expect the worst and go in weapons at the ready.
Come on, it wouldn't hurt to try.