NAtional Parks are off limits when operating from land under the parks authority.
You can overfly it though, and keep to FAA drone rules . . . bear in mind that doesn't allow too long a flights into the parks as VLOS would be say 500m max ?
Maybe a bit further with strobes.
Funny you ask about the Grand Canyon as it does have at least some no fly zones allotted to it by the FAA . . . don't think it's ALL the park, but the high tourist flight corridors and other such areas.
A small section of map with a NFZ was posted in another thread recently, maybe someone US based can do this again for you.