The elevators that carried President Obama 750 feet down into the caves of Carlsbad Caverns on Friday were working again, just in time for the first family's visit.

Out of service until last month, the elevators were part of the National Park Service's backlog of overdue maintenance projects. One of the government's most popular programs, with a record 307 million visitors in 2015, is showing its age: a record $12 billion in deferred maintenance.

That backlog has grown during Obama's presidency as Congress has refused to increase funds for the parks.

"It's old and cantankerous," park service spokesman Jeffrey Olson said of the elevator system at Carlsbad Caverns. "And there are things like that all over the park service."

The Obama family visited Carlsbad Caverns on Friday and will tour Yosemite National Park on Saturday.

"How cool is this?" Obama exclaimed as a National Park Service employee led the family on a tour of the caverns' Big Room, nearly 800 feet deep into the limestone.

Obama gazed at the stalactites, stalagmites and various other formations, and said that it was "spectacular."

Interior Secretary Sally Jewell said Thursday that the Park Service is "relying more on donations every single year. And what used to be a donation to provide the margin of excellence is now really the margin of survival for a lot of these parks."

At the caverns, where three of the 119 caves are open to the public, officials say they need about $44 million to permanently fix the elevators and make other necessary upgrades. At Yosemite, park officials have delayed more than $555 million in maintenance, including upgrading leaking sewer lines and rehabilitating the Mariposa Grove of Giant Sequoias.

While Obama's last two budget requests included more money for the parks during their centennial celebration leading up to August's anniversary, Congress has not approved the full amount.

As the maintenance backlog has grown — up $440 million just last year — the park service has considered new funding options, including changing its policy to allow closer relationships with corporate partners.

The NPS released a proposal in March that would allow corporate donors to have logos displayed in parks. It has waived its policies against partnering with alcohol companies and allowing company logos on park vehicles.

Congressional funding for the park service fell 8 percent between 2005 and 2014.