South Dakota state parks try to pull the same misinformation. Open and concealed carry are both legal in South Dakota state parks, open for anyone and concealed with a permit.
However, the brochure they give you at the park entrance states you cannot carry a loaded firearm in the park. The brochure is wrong!!!! You can!
I carry openly and concealed in Custer State Park everytime I go there which is often as I live just a few miles outside of the park. I am waiting for the day that a ranger challenges me for openly carrying which I do whenever I hike in the park.
I don't know about Colorado but I would guess their park system also is either mistaken or just publishes a falsehood knowing full well that it is incorrect information.