Not sure about those areas in Wyoming, but I think the .270 is a good choice for the rifle season, personally prefer .308, since that is what I have! A shot under 200 yards would be close, very close! With a bow, you will need a good blind near water or feed, and a lot of luck! If you are coming out through Nebraska on I-80, drop a message and maybe we can meet up for a break. We are in Chappell between Ogalalla and Sidney.
Hawkdancer