 "President Barack Obama, Malia Obama, Michelle Obama and Sasha Obama walk to board Air Force One after leaving Yosemite National Park via helicopter after visiting the park to celebrate the 100th anniversary of the creation of US national park system.")
President Barack Obama and the first family are hiking at Prince William Forest Park in Virginia. Their visit comes as the National Park Service's celebrates its centennial.
The president has marked the week by creating a national monument in Maine and expanding a monument off Hawaii. Admission to national parks and historic sites was free during the weekend.
The National Park Services describes Prince William Forest Park as a "respite of quiet and calm" amid the hustle and bustle and frequent traffic jams of northern Virginia.
The agency says the park has 37 miles of hiking trails that meander through some 15,000 acres. It is the largest protected natural area in the Washington region.
