Top 10 Things You Didn't Know About National Parks

Explosions in the Desert
White Sands National Monument spans more than 275 sq. mi. of New Mexico desert and contains the largest gypsum dune fields in the world. But because the park lies adjacent to the country's largest military installation — a 3,200-sq.-mi. missile range — the crystalline waves are often closed to the public while the Defense Department conducts top-secret (and presumably highly dangerous) tests.

• Ken Burns, American Filmmaker