their participation in this federal program is voluntary.

The legislative authority for the National Natural Landmarks Program stems from the Historic Sites Act of August 21, 1935 (49 Stat. 666, 16 U.S.C. 641); the program is governed by federal regulations. The NNL Program does not have the protection features of Section 106 of the National Historic Preservation Act of 1966. Thus, the designation of a National Natural Landmark constitutes