Tens of thousands of dollars from outside political groups have flowed into Garfield County elections this year, mostly in favor of Republican candidates. It appears to be the first time such outside money has entered a county race in Colorado, and while these groups have been secretive, they may be operating perfectly legally.

“The fact that they haven’t filed anything doesn’t necessarily mean they have broken any laws,” said Luis Toro, general counsel for the watchdog group Colorado Ethics Watch.

He said his organization is looking into concerns about the groups operating in Garfield County, but it’s not clear they’ve violated the law.

At least six outside political groups have muscled in on the county races, where oil and gas issues have become a sharp dividing line between Republicans and Democrats. Most have disclosed very little about their donors, and most don’t have to.

Several appear to be registered as 501c4 nonprofit groups, which have to disclose very little about who their donors are or how their money is spent.

“It’s a new development to see these groups down at the county commissioners level,” Toro said. “This is the only one I’ve seen.”

The latest to enter the fray is Western Tradition Partnership, a conservative nonprofit group based in Bozeman, Mont., that favors natural resource extraction. The group has sent out mailings that criticize Democratic commissioner candidate Stephen Bershenyi, linking him to environmental groups and noting his opposition to the controversial Red Feather Ridge development that was shot down outside Glenwood Springs.

Bershenyi questions the legality of these groups.

“I think what the larger concern is their presence in the race to begin with,” he said, “and for them to be so secretive just heightens my suspicion about who they are and where the money’s coming from.”

It’s not clear that they are doing anything illegal, though.

Under state law, so-called 527 groups, political groups that work on behalf of candidates or issues without being directly involved with their campaigns, don’t have to report their activities until after they’ve started work. Those that got under way after Oct. 23 won’t have to file until Dec. 4, long after the races are decided.

Groups that are 501c4 nonprofits have to disclose very little.

Most political groups have 60 days file an electioneering report with the state. Only three groups have done so, so far.

At least four of the six groups appear to be 501c4s, meaning little may be known about their fundraising and expenditures.

These nonprofit groups have come to replace so-called 527 organizations as the favored shell for political contributions, Toro said. They have no contribution cap and don’t have to reveal who their donors are. They became popular after 527s faced greater disclosure requirements at the state and national level, Toro said, but unlike other political groups, they have to spent at least half of their money on non-political activities.

So-called 527s, because of the section of the tax code they fall under, lack the spending caps that other political groups have, but they must now release contribution and expenditure information.

According to filings with the secretary of state’s office, WORC Colorado Rural Voters has spent $15,000 on door-to-door campaigns, mailings and phone banks on behalf of Democrats Bershenyi and Steven Carter. The group is a 501c4, and an arm of the Western Organization of Resource Councils, an umbrella group of environmental organizations including Western Colorado Congress and the Grand Valley Citizens Alliance.

The group Western Heritage, funded by the chairman of the energy company Antero Resources and Scott McInnis, an energy company lobbyist and Glenwood Springs native who was a popular Republican legislator, appears to have spent $10,000 each on advertising campaigns for Republicans John Martin and Mike Samson. State records indicate it is a 501c4, but it has indicated its donors.

The group Small Town Values, a Denver-based group registered to John Zakhem, the attorney to the state Republican Party, has spent $7,250 on advertising for Samson and Martin. It is also a 501c4, and like the other two groups, has filed electioneering reports, but it hasn’t listed its donors.

Zakhem said the organization had not authorized him to release information about its members.

Other groups have spent undocumented amounts of money on behalf of Republican candidates and have so far filed no electioneering reports.

Western Tradition Partnerships is a 501c4, and although it is based in Montana, it has an office in Denver. A message seeking comment was not returned, but its Web site describes its interest in local elections.

“There’s no question that decisions at the State and County Commission level can be even more unexpected — and more damaging — than those taking place in Congress,” it says. “Many well-heeled organizations are taking aim at the independent Western way of life.”

The group was founded by former Rep. Scott Marlenee, R-Mont., and Montana state Rep. John Sinrud, also a Republican.

Two other groups, the Colorado League of Taxpayers and the Coalition for Energy and Environment, have no records with the secretary of state’s election division, but IRS records list them as 527 groups.

Those groups have listed Scott Shires, a GOP operative, as its registered agent. Shires has been fined in the past for his attack ads. He did not return a message seeking comment.