The groups nevertheless fear that environmental problems around communities and national parks will stem from cyanide, arsenic and acid used to extract metals such as gold and silver should only a small percentage of the claims evolve into actual mining operations.

"The data shows that claims and communities are on a collision course in the West," said Jane Danowitz, director of the Pew Campaign for Responsible Mining, which produced the report along with the Environmental Working Group.

Their analysis shows that hard rock mining claims within five miles of cities and towns have increased by 47 percent since 2003, from 35,350 to nearly 52,000.

Mark Amodei, president of the Nevada Mining Association, an industry organization that includes mining operators, said the statistics are deceiving because merely staking a claim is the first step in a lengthy process that may or may not become a mining operations.

He said the study "ignores the exploration process and the permitting process that goes through federal, state and local authorities. And it ignores whether there are minerals in the area that are economically extractable."

A closer look at the environmental groups' data shows that the 5,822 mining claims within five miles of residential areas listed for the Las Vegas metropolitan statistical area encompass a 39,677 square-mile swath of the Southwest that's larger than Indiana. Spread across Clark and Nye counties and Mojave County, Ariz., that translates to 6.8 claims per square mile.

Included in the 5,822 claims are 1,049 near Beatty, 824 near Moapa Valley, 561 near Tonopah, and 211 near Gabbs, a mining town in Nye County, 320 miles north of Las Vegas.

Passage of the 1998 Southern Nevada Public Land Management Act has precluded new mining claims in the so-called disposal area of the Las Vegas Valley where public lands have been auctioned.

Dusty Horwitt, senior analyst for public lands at Environmental Working Group, said he's not aware of any active, hard rock mining operations that have resulted from claims in the valley or on its fringe.

He said it would be impossible to discern the motives of people who file mining claims in the path of sprawl.

"But there have been cases in the past where people have staked claims for speculative purposes and for purposes other than mining," he said.

Horwitt offered an instance that drew attention in the late 1980s. Prospector Anthony Perchetti of Tonopah staked a series of gold claims for $500, and eventually was paid $249,500 by the Department of Energy to give them up. The claims were at Yucca Mountain, where DOE had decided to place a nuclear waste site.