I far from trust the soldiers that they encounter on the air field at Irwin. I understand a commander not being available. Even without Zs everywhere, my commander can take days just to return a phone call. One of the things that lends credibility is the corporal that shows up says his MOS is 31B, military police. Assuming his commander is a real commander and has come up through the officer ranks, he would know that detainee operations and searching prisoners/new comers is perfectly suited to an MP unit, as opposed to sending a signal team or a pair of cooks. Fort Irwin also has plenty of MPs, as well as a Cavalry regiment, so it's not unrealistic that they were able to sustain themselves for a long time with little stress to the lower ranks. Also, geographically Fort Irwin is out in the middle of nowhere. It would be a great place to set up for a herd of Zs if you wanted to see them coming. The downside is getting back out off post to look for supplies or survivors. It would be a multiple-day excursion just to get to LA, never mind trying to accomplish a search and rescue.