Like Ron Swanson, we don't know when national parks will return to regular functioning or re-open shuttered facilities and campgrounds. President Trump has suggested it could take "months or even years" for the government shutdown to end.
One of the controversies surrounding the current shutdown is that the Trump administration has elected to keep national parks open, but they lack enough staff to run normally.
So major national parks like Yosemite, Yellowstone, Acadia, and Death Valley are still accessible to visitors, but have canceled certain services like bathroom cleaning and trash collection.