50 caliber minimum for elk in CO, and you'll have the best selection of bullets in 50 cal. so that's what I'd recommend unless you want to shoot round balls, then something bigger would be better. If you don't know the regs, no scopes allowed, fiber optic sights are OK, no sabots, pelleted powder, or smokeless.
Idaho's about the same with an addition - no 209 primers. It's caps or flint only. You have to be able to see the cap when it's cocked. Peep sights are allowed along with fiber optics.
