“We don’t have a choice,” said Jack Burns, who has worked in Zion since 1982. “We have to do something. If this going to remain a place of special importance for generations, we have to do something now.”

The National Park Service was created in 1916 to protect the country’s growing system of parks and monuments. Its mandate is to conserve scenery and wildlife while also protecting visitor enjoyment for generations to come. For years, the lack of a reservation system for park entry aligned with the service’s ethos of democracy and discovery: Anyone could come, pretty much anytime. (The service has long required permits for hiking in more remote areas.)

But lately, both visitors and nature are suffering. Mr. Burns, who is on a team that is considering a reservation system, said some people showed up for a vacation they had planned for months, spent a day in the gridlock and turned around. Rangers, stressed by the frustrated masses, have started a monthly meeting to discuss “visitor use” that some say has turned into a group-therapy session.