Whew thats a tough one. Generally, preemption would rule thereby allowing valid permit holders could CC. If these are National Parks, then CC/OC is a no-no. I honestly don't know the rules with National Registered Historic Places.
IANAL, but I would think that since they are NOT in Denver County, CC (with CCW) would be legal via preemption. Since there is signage, OC would probably not be a good idea, at least until further researched.
Great topic/question by the way, good job and welcome to the forums!