Well, to cover every single area that is in the real world would be exhausting, Fresno probably just never got noticed. It's also entirely possible that Fresno just never got rebuilt after the war, fading into memory.
Most likely, Fresno was indirectly destroyed by the nuclear rain that came after the bombs fell. The radioactivity poisoned the soil, making it useless for the agriculture industry that it was centered around.
The likelyhood that a vault was built around is small, and more likely than not establishments were built around the Vaults, because it's easier.