SALT LAKE CITY » The U.S. Bureau of Land Management has begun an investigation that could lead to charges against nearly 50 people who rode ATVs on an off-limits trail last weekend in Utah to show their displeasure with the federal government.

The agency is working to determine who broke the law and what happened Saturday, Bureau of Land Management spokeswoman Megan Crandall said. A damage assessment is planned of Recapture Canyon, home to dwellings, artifacts and burials left behind by Ancestral Puebloans as many as 2,000 years ago before they mysteriously vanished, she said.

The agency warned riders all week to stay out, vowing prosecution against those who ignore a law put in place in 2007 after an illegal trail was found that cuts through the ancestral ruins. The canyon is open to hikers and horseback riders.

Bureau of Land Management law enforcement officers were at the protest in plain clothes recording and documenting who was there, said Crandall, who added that the agency remains committed to holding the riders accountable.

The U.S. Attorney’s Office in Salt Lake City is waiting to see what information the agency sends before commenting on possible charges, spokeswoman Melodie Rydalch said.

Following a similar ATV protest ride in 2009 on a different off-limits trail, the agency sent the results of an investigation to the U.S. Attorney’s Office in Utah. But federal prosecutors didn’t file any charges.

The U.S. Attorney who oversaw the office then is no longer around. His replacement, David Barlow, is leaving the post this summer after three years to return to private practice.

San Juan County Sheriff Rick Eldredge said 40 to 50 ATV riders went on the trail, many of them waving American flags and some carrying weapons. There were no confrontations or arrests during what was a peaceful protest. The canyon is about 300 miles southeast of Salt Lake City near junction of Utah, Arizona, New Mexico and Colorado, known as the Four Corners.

The protest organizer, San Juan County Commissioner Phil Lyman, said the ride was a demonstration against the federal government’s overreaching control of public lands. He and others want the trail re-opened to ATVs.

Great Old Broads for Wilderness, a Colorado-based group that opposed the ride and believes the trail should remain off limits to preserve the ecology and artifacts, called on federal prosecutors to send an important message and level charges against the protesters.

"It’s not appropriate to break the law, do an illegal ride and go into the canyons with weapons," executive director Shelley Silbert said. "That’s very different than a non-violent, civil disobedience protest."

The controversy over the ATV ride in Utah came after the Bureau of Land Management had a confrontation last month with Nevada rancher Cliven Bundy. In Nevada, armed people who describe themselves as a militia have rallied around rancher Bundy, who doesn’t recognize the authority of the federal government and hasn’t paid grazing fees since 1992. The Bureau of Land Management stopped trying to round up his cattle after a showdown with hundreds of Bundy supporters.

The Oregonian newspaper reported Sunday that each year, Oregon ranchers whose herds graze on public ranges overseen by the U.S. Bureau of Land Management pay the federal government fees that are about equal to what Bundy owes in back fees and penalties — more than $1 million.

The Oregon ranchers are prompt to pay, the bureau told The Oregonian.

Utah ranchers and county leaders recently threatened to break federal law and round up wild horses this summer if the Bureau of Land Management doesn’t do it first. Earlier this week, an employee of the federal agency in Utah was threatened while driving on the highway by two men with a weapon holding a sign, "You need to die."

The federal government owns two-thirds of Utah’s land. The Republican-dominated Legislature passed a law in 2012 that demands the state be given control of those lands before 2015, excluding national parks.