Actually, the eastern half of CO is just a gentle walk uphill, effectively a continuation of Kansas. Plenty of mountain folk sprinkled in small cities who are very independent minded. Get to the Front Range and you have access to half the population and haven't had to go into the mountains yet.
Utah on the other hand has as many of the gun mountain folk, have a non-secular doctrine to wrap themselves around as well as high mountains and extensive high desert to cross. They have also, as a community, been preparing. Just in case. To the extent that many houses have cold storage rooms and some 2 years of emergency supplies. Its expected of a good Mormon.
My vote would be Utah or Idaho. Idaho has a LARGE collection of anti-govt extremists. State war would be a wet dream for a lot of folks, they have geography on their side as well. However, half the population of Utah, which is about half the population of CO.