Religion in the national parks is a white-hot topic. Just mention that park rangers at Grand Canyon National Park can't discuss the geologic age of that canyon, as PEER suggested late last year, and you'll draw a crowd.
Controversy aside, the National Park Service officially does not endorse one religion over another, or even religion, for that matter. But it doesn't outlaw it, either. Proof of that can be found at the Grand Canyon, where the park leases out a building for religious services, as well as for concerts and meetings.
Called quite innocently the Shrine of the Ages, the nondescript rock-faced building plays musical chairs with religious services offered by the Latter-Day Saints, Catholics, Baptists, and a community congregation.