FAR 91.119 (d)
Helicopters may be operated at less than the minimums prescribed in paragraph (b) or (c) of this section if the operation is conducted without hazard to persons or property on the surface....
AIM 7-4-6 (b)
Pilots are requested to maintain a minimum altitude of 2,000 feet above the surface of the following: National Parks, Monuments....
Don't have a sectional of that area, either. However, if he was flying below 2000 AGL over that National Park, you can stick a fork in him because he is DONE. AC 91-36 defines that area as noise sensitive, and flight is prohibited below 2000 AGL. Even though the AIM says "pilots are requested," the Advisory Circular for VFR flight is a bit more specific. There are other Federal statutes I'm sure they'll use against him, too.