Often called "America's best idea," the nation's 400-some national parks, monuments, and refuges are more popular than ever, but they face crumbling buildings and lean budgets, Interior Secretary Sally Jewell warned at National Geographic headquarters Tuesday, during National Parks Week.

"At a time when our public lands face serious threats, from land grabs to climate change, we can't afford to turn our back on them," Jewell said at an event celebrating the hundredth anniversary of the U.S. National Park Service. "We need to use this centennial to set a new path for conservation." 

Jewell said the national parks maintenance backlog has reached nearly $12 billion, the worst in the system's history. That has meant roads out of service and shuttered bathrooms, as well as cuts in staffing and programs.                                                     

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