President Barack Obama and the first family celebrated America's cherished natural heritage Saturday during a weekend tour marking the 100th anniversary of the nation's vaunted national park system.

Obama, also using the occasion to tout his environmental record, is the first sitting president since John F. Kennedy in 1962 to visit California's Yosemite National Park.

Obama has made protecting nature areas one of the hallmarks of his presidency.

Since 2009, he has set aside as protected areas more than 265 million acres (100 million hectares) of public lands and waters across the country, more than any of his predecessors did. A large part of that involves a marine sanctuary around islands and atolls in the Pacific.

In doing so, he relied on the Antiquities Act, a law signed in 1906 by then president Theodore Roosevelt, a fervent advocate of preserving the country's natural resources.

For Obama, who has made the fight against climate change a priority of his two terms in office and complains of systematic obstructionism by the Republican-controlled Congress, the law has been key to circumventing his opponents on environmental issues.

It allows the president to move swiftly to preserve threatened areas, which can be transformed into national parks if Congress gives the go ahead.

The Grand Canyon, Death Valley and vast swathes of Alaska have benefited from the law.

Before Obama, 16 presidents have used the measures. Only three, all of them Republicans, did not do so: Richard Nixon, Ronald Reagan and George H. W. Bush.

Before leaving office in January, Obama could sign off on other protection projects awaiting his signature, such as an expansion of the Papahanaumokuakea marine reserve in Hawaii, declared a decade ago by George W. Bush and home to many endangered species.

Over the years, such presidential designations have often triggered conflicts because they end up prohibiting exploration and development of fossil fuels such as oil, natural gas and coal on the protected lands or in protected waters.

Some lawmakers question the legal foundation of the Antiquities Act and what they see as a carte blanche for the president.

These lawmakers complain of poor management of federal lands and stymied economic development. They have tried in vain several times to have the law erased.

But the national park system remains hugely popular in the United States. The 400-odd parks received a record 305 million visitors last year. The system turns 100 on August 25.

"We have more work to do to preserve our lands and culture and our history. We're not done yet," Obama said in a speech against the spectacular backdrop of Yosemite Falls, the highest waterfall in the park.

"For this centennial, we're asking all Americans to find your park so everyone, including those from underserved communities, can experience these wonders."

- 'Spectacular !' -

On Friday ,the president and his family visited Carlsbad Caverns National Park in New Mexico, which features more than 100 caves, three of them open to the public.

The Obamas visited the Big Room, a large cave chamber located 754 feet (230 meters) underground and filled with stalactites and stalagmites. It is also a sanctuary for hundreds of thousands of bats.

"Spectacular," Obama said.

"How cool is this?", he added as he turned to journalists, although the comment seemed aimed more at his teenage daughters, Malia and Sasha.

Several hours later, after flying over waterfalls and granite peaks, the first family traveled to Yosemite, known for its giant redwood trees.

At one point, he and first lady Michelle stopped to chat with some kids at a park facility under bright, sunny skies and Mrs Obama asked them what they would do to scare away bears.

As the kids started yelling, the president said: "Oh, I would get out of here!"

The Obamas then sat on the ground for a photo with the group, with the president making sure all kids were smiling.

"Everybody say cheese," he said. "Everybody say 'national parks.' Everybody say 'happy birthday,'" he added, mentioning a birthday girl in the group.

"Who is going to help me up now?" he added.

The family outing is reminiscent of one the Obamas made in 2009 to Yellowstone National Park in Wyoming.

With seven months left in Obama's second and final term, environmental groups are urging the president not to rest on his laurels when it comes to protecting nature.

"What he has done so far has been significant," said Sharon Buccino of the National Resources Defense Council.

"But the real measure of his conservation legacy is going to be judged based on what he does with his remaining time."

Source: AFP