Actually, PastryGoddess, add South Dakota to that list. They've opened Mount Rushmore back up to the public as well.
Still, this woman is an SS. Minimal amounts of rangers on staff are essential employees. They need to be there to spot fires, to watch for people coming in so they can be turned away, they need to be there to make sure nobody gets in and vandalizes the facilities, making it more expensive for the parks to be re-opened in the future. Also, some people live inside national parks, and even with the parks shut down, they have to have access to their homes, so all the roads may not be blocked off all the time.