YOSEMITE NATIONAL PARK (UNITED STATES) - President Barack Obama and the first family are celebrating America's cherished natural heritage, making a weekend tour marking the 100th anniversary of the nation's vaunted national park system.
Marine One -- carrying the US first family -- flies past 'Half Dome' at the Yosemite National Park
Obama, also using the occasion to tout his record on the environment, is the first sitting president since John F. Kennedy in 1962 to visit 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 of public lands and waters (100 million hectares) across the country, which is 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 a good way to get around 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 law. 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 a marine reserve in Hawaii that is called Papahanaumokuakea, 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.
- 'Spectacular !' -
"Spectacular!", the president said Friday as he visited Carlsbad Caverns National Park in New Mexico, which features more than 100 caves, three of them open to the public.
The Obamas visited one called the Big Room, which is 754 feet (230 meters) underground and filled with stalactites and stalagmites. It is also a sanctuary for hundreds of thousands of bats.
"How cool is this?", Obama said 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 National Park in California, known for its giant redwood trees.
The family outing is reminiscent of one the Obamas made in 2009 to Yellowstone National Park in Wyoming.
The park system turns 100 on August 25.
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," she added.
The long family weekend comes after the nation was shocked by the worst mass shooting in US history -- the death of 49 people in a shooting at a gay nightclub in Orlando, Florida last Sunday.
And before flying out West, Obama saw his Syria policy challenged by 50 State Department diplomats who signed a memo criticizing US treatment of President Bashar al-Assad as too soft, and calling on the United States to use military force against his regime.