That and they know they came from L.A. as I believe
Tanya and
Marcus seemed surprised they managed to survive in the city. They know that the range is probably within 50-60 miles (or whatever it was
Glenn said the CB would reach).
Michael had apparently drawn a map too that they used to get
back to
the tower, but who knows who may have seen it? It's not p Ppunreasonable someone had already found and read one of their
journals too.
Even if they didn't have access to those last two things, they still have good reason to send out recon teams to thouroughly hunt for them as they stole most of their ammo and know a secret that would garuntee
Gatekeeper's reign wouldn't last long...