ALMA, Colo. -- The U.S. Forest Service has stopped issuing permits to groups seeking access to four of Colorado's most popular fourteeners because the trails to the summits cross private land.

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The agency this week began distributing fliers warning hikers to keep off trails to Mount Democrat, Mount Lincoln, Mount Bross and Mount Cameron in Park County unless they have permission from landowners who acquired the land through old mining claims.

"The bottom line is there is no public access to those peaks," Sara Mayben, head of the Forest Service's South Park Ranger District told The Denver Post. "We can't stop the public from trespassing, but we will take steps to make it clear that they are."

Their proximity to Denver and their relatively low skill level have made the peaks among the most popular of the state's 54 mountains taller than 14,000 feet.

Terri Gifford drove from Illinois to climb the four peaks in the Mosquito Range. She was surprised to learn they were off-limits.

"Are we not supposed to be up there?" Gifford asked as she rummaged for a map in her van parked by the Kite Lake trailhead. "It's in all the guidebooks."

Access to at least two other fourteeners -- Culebra Peak in the Sangre de Cristos and Wilson Peak near Telluride -- is at issue because of the 1872 Mining Act, a Civil War-era law meant to develop the mineral wealth of the Western States, said T.J. Rapoport, executive director of the Fourteeners Initiative. The original claims were patented, meaning they were transferred to private ownership.

Interest in the fourteeners has soared in recent years, with roughly half a million people climbing at least one each year.

Maury Reiber, one of the private landowners in the four peaks area, said he's concerned he will face lawsuits if someone falls into one of the mine shafts that dot the slopes.

"We're trying to keep an open mind about different solutions, but these issues need to be addressed," Reiber said. "If we have to be hard-nosed and say, 'No one goes up there,' that's the way it's got to be."

Local officials have joined together to form the Mosquito Range Heritage Initiative, which among other goals is seeking to work out access agreements with land owners.

"We have a compelling economic interest in seeing that these peaks remain open," said Richard Hamilton, a former county planner who works at the historic Hand Hotel.

In an average year, hikers book more than 250 nights at the 11-room hotel, he said.

"I don't want the guy with a mining patent to face a huge lawsuit," Hamilton said. "But this is a huge taking of a public resource."