The administration must decide by July whether to extend a two-year respite on thousands of mining claims in areas around the Grand Canyon, Mount Rushmore, Joshua Tree national park and the area around Yosemite national park. If it does not, there is nothing to stop mining interests from drilling on its claims around the canyon, the report warns.
"These claims are all still active, and there is nothing right now that the government can do to prevent them from becoming mines," said Jane Danowitz, who works on public lands protection for Pew.
Obama moved to protect public lands soon after coming to the White House, calling a two-year halt to mining in sensitive areas.
The interior secretary, Ken Salazar, must now decide whether to extend the ban. But environmental organisations argue Obama had already demonstrated reluctance to take on a fight with Republicans over protecting America's natural heritage.
Under a spending deal reached last week, Obama agreed not to use money from a newly launched wilderness initiative that would have protected 7.3 million acres of land from drilling.
Critics argued the initiative had only been launched last December, and had not been allotted funds, so the funding ban would make no impact on reducing the deficit that Obama is targeting.
The last five years have seen a 2,000% increase in mining claims in the west. More than 8,000 mining claims have been staked in the Grand Canyon alone – mainly by major international companies rather than the pick and shovel claims of yore.
The claims are a legacy of America's antiquated mining laws, which were written to lure newcomers to the west.