From Acadia in Maine to Zion in Utah to the North Cascades in Washington, America's 401 national park areas have gates blocking entrance roads.
The last remaining campers and hotel guests in the parks must leave Thursday, and park rangers will patrol to keep others out.
The national parks "belong to the American people, and the American people should have the right to come in," says National Park Service Director Jonathan Jarvis. "But the only way I can protect these places during this period is to shut them down."
The Senate is considering legislation to prevent a global helium shortage from worsening in October. That's when one huge supply of helium in the U.S. is set to terminate. The House overwhelmingly passed its own bill last month to keep the Federal Helium Program going.
That was a relief to industries that can't get along without helium. The gas is used in MRI machines, semiconductors, aerospace equipment, lasers and of course balloons.
Secretary of Interior Ken Salazar says he will tighten regulations of the federal government's wild horse program, restricting the number of horses people can buy and making it easier for the government to prosecute buyers who sell mustangs to slaughter.
A southern Colorado man under investigation for his handling of protected wild horses has admitted to state regulators that he shipped animals out of Colorado in violation of brand inspection laws, officials said.