On the topic of concealed carry in Boulder Open Space from the Bouler City Attorney Tom Carr:

This is a complex area of Colorado law. Under the Colorado Constitution, home rule cities such as Boulder have an exclusive right to legislate over matters of local concern. The Colorado Supreme Court has never decided whether the regulation of firearms is a matter of statewide or local concern. There was one case involving Denver on which the court split 4 to 4. The attorney general ruled that this meant that the case had no precedential effect...