By Roberta Rampton

CARLSBAD CAVERNS NATIONAL PARK, N.M. (Reuters) - U.S. President Barack Obama and his family escaped the blistering heat of the Chihuahuan Desert on Friday when they went through a maze of ancient caverns where the only sound was the drip-dripping from stalactites.

The subterranean adventure was the first stop on a working vacation during which Obama will spend some time with his teenaged daughters while making the case for more spending on conservation and curbing climate change.

It was just like any other family holiday, except the entourage of Secret Service agents, aides and press who follow Obama wherever he goes had to descend the 754 feet (230 m) on elevators in eight shifts.

"How cool is this?" he said to the press in the dark, damp alien landscape of the "Big Room," the best known of the labyrinth of limestone caves that actor Will Rogers once called the “Grand Canyon with a roof on it."

The president is helping celebrate the centennial of the National Park Service while highlighting his plan to reduce climate-changing carbon emissions, which he sees as part of the legacy of his time in office.

The White House has said the changing climate evidenced by droughts, increased flooding and wildfires and stronger storms has put national parks at risk.

The Obamas were due to fly west later on Friday to the Sierra Nevada mountains and Yosemite, the country's oldest national park and one of its most popular landmarks.

Visits to national parks have surged due in part to lower gasoline prices.

Still, roads, sewer systems and visitor centers in national parks are aging, and the government is grappling with a $11.5 billion backlog of maintenance projects.

At Carlsbad, elevators broke down in 2015, though they seemed in good shape for the Obamas' descent.

During his time in office, which will end on Jan. 20, 2017, Obama has added 20 sites to the national park system, protecting more than 265 million acres of public land and water and historic sites with new parks, monuments and restrictions for development, more than any other president.

Interior Secretary Sally Jewell said national park visits in 2016 were on pace to beat last year's record of 307 million. Tourists contributed an estimated $300 billion to the economy, supporting about 2 million jobs, she told reporters.

She wants Congress to remember those numbers as it considers investments in public lands.

Republicans have slammed Obama for adding sites at a time when the government does not have enough funding to look after existing ones.

"To me, there is little point in conserving lands or allowing the federal government to acquire even more land if we are not going to take proper care of them," Senator Lisa Murkowski, a Republican from Alaska who is the chairman of the Senate Energy and Natural Resources Committee, said last year.

(Additional reporting by Timothy Gardner in Washington, D.C.; Editing by Toni Reinhold)