Can a microclimate really allow a person to survive like Ann Burden did in the book of Z for Zachariah written by Robert C. O'Brien? She lived in a valley which she thinks was the only area which avoided the radiation.  Exactly how the valley escaped contamination is unclear, though Ann at one point recounts people saying that the valley "has its own weather." I was just wondering (considering the valley has a microclimate) if it would actually be possible for an instance like this to occur? Could radiation just completely miss a valley like this?