They are extreme versions of the self-reliant, independent-thinking frontiersmen who have long roamed the American West.

From wanted criminals to the more eccentric "Phantom Pooper" or "Dugout Dick," a wide range of outlaws and drifters live off the land in the rugged Rocky Mountains, folk heroes to the militia movement and a source of chagrin for law enforcement.

Among the more storied is Troy James Knapp, 44, a loner wanted for burglaries of resort cabins near Zion National Park in Utah. In his five years in the wild, he has lived off land so rugged the average visitor stocks his four-wheel drive with emergency supplies.

Legend about Knapp's uncanny outdoor skills and hardiness has grown along with the thefts he is accused of committing - frequently of firearms - and the threats he has made against a local sheriff in the forested high country of southern Utah called Cedar Mountain.

The snowshoe-clad survivalist has out-manoeuvred authorities in manhunts, one as recently as last month when a reported sighting of a rifle-toting figure sent police in camouflage and bullet-proof vests pouring into the woods on foot and by air.

Knapp is one of a number of fugitives thought to be holed up in the vast back country of the Rocky Mountains, a region where self-sufficiency is almost a religion and separatist and militia movements have found fertile ground.

The forbidding mountainscape has given rise to characters such as 19th century trapper and explorer Kit Carson, and has acted as a magnet for modern-day mountain men and outlaws such as Claude Dallas.

Dallas was convicted in 1982 of manslaughter in the slayings of two Idaho game wardens investigating him for poaching while living off the canyon lands of southwestern Idaho.

After the killings, Dallas fled into the wilderness and eluded police for months. During his time on the run, he gained cult status among anti-government militiamen and was portrayed in a popular ballad as a renegade hero.

FOLK HERO OR CRIMINAL?

Aided by survival skills a U.S. marshal has likened to those of American frontiersman Davy Crockett, Knapp and a handful of other back country drifters are folkloric figures to fiercely anti-authority loners and groups of the American West, and their hostility seems to centre on law enforcement officials.

In Cedar Mountain, the spectre of an armed loner who may harbour extremist views has stoked fear among seasonal residents and vacation homeowners from Las Vegas.

"This guy is not a folk hero, he's a dangerous criminal," said Jud Hendrickson, whose family getaway property straddles the area where Knapp is known to roam. "People are going to get hurt before this is over."

Authorities say break-ins mostly occur in winter, when the frigid weather and deep snow drive Knapp indoors in search of food, equipment and guns.

Those weapons have reappeared in what Iron County, Utah, Detective Sergeant Jody Edwards calls "doomsday stashes" in camps Knapp erects deep in the woods in mild weather.

Knapp runs trap lines, shoots squirrels and has trekked across hundreds of miles of harsh terrain. He is uninterested in valuables many thieves would prize, said Michael Wingert, supervisory deputy for the U.S. Marshals Service in Utah.

"If a cabin owner left a gold brooch on the table, he probably wouldn't touch it," Wingert said. "Outside of reading about Davy Crockett, I can't tell you the last time I've encountered a case like this."

In Montana, authorities are following up on hundreds of tips on the whereabouts of former militia leader David Burgert, 48.

Burgert is wanted on attempted murder charges for a shootout with Missoula County deputies in June, when authorities say he fired a handgun at officers before escaping into the tangled back country of western Montana.

Missoula County Undersheriff Mike Dominick said Burgert, sentenced in 2004 to seven years in federal prison on weapons charges, is a survivalist able to fend for himself in the wilds.

"He's in desperate circumstances and we believe him to be a particular problem for local law enforcement. His animosity is directed at us," Dominick said.

OPEN SPACES

The challenge in the wide-open spaces of the western United States is telling the difference between harmless hermits and recluses - and dangerous sociopaths. While the behaviour of eccentrics in the western hinterlands may be objectionable, it isn't usually criminal, authorities said.

Police in Idaho have grappled with the socially unacceptable behaviour of individuals like the "Phantom Pooper," who defecated on properties in the Frank Church River of No Return Wilderness.

Then there's "Dugout Dick," a squatter on public lands who irrigated his asparagus crop with urine, and rented out caves he carved into the rocky outcroppings above the Salmon River.

"There are plenty of people with anti-social behaviour out there who never really bother anybody," said Tony Latham, a retired Idaho Fish and Game investigator.

The Southern Poverty Law Center released a report on March 8 showing a sharp rise in anti-government groups between 2010 and 2011. The report came after an FBI warning in February that extremists opposed to the central government pose a growing threat to local law enforcement.

Such "sovereign citizens" were mostly known for filing arcane lawsuits against government officials, refusing to pay taxes and displaying phony license plates before May 2010, when two Arkansas police officers were gunned down during a traffic stop of a member of the movement.

"That was a wake-up call for everybody," said Don Robinson, FBI supervisory special agent in Idaho.

Police are the preferred targets, said Mark Potok, senior fellow at the Southern Poverty Law Center.

Extremists espouse a patchwork of beliefs where one conspiracy about the government overlaps another, Potok said, and the worry is knowing when "today's eccentric becomes tomorrow's building bomber."

Militias movements tend to come in waves, like that which spiked in 1995 when Oklahoma City bomber Timothy McVeigh killed 168 people. A second wave of separatist activism began in early 2009 after the election of an African-American president with a foreign-sounding name.

The rebirth of fringe movements may also be linked to the economic downturn, fears that Democratic leaders will impose new restrictions on guns and ultra-right rhetoric in the media, he said.

The FBI's Robinson said what concerns authorities most is the "lone offender," the under-the-radar extremist who suddenly surfaces in an act of spectacular violence.

Police also worry about what they call the "time bomb," the sometime offender whose potential for violence escalates over time. That's how Edwards, the Utah detective, views Knapp, who recently pledged to put a neighbouring sheriff "in the ground" in a note left behind at a burgled cabin.

"We have a dangerous situation on our hands," Edwards said.

(Editing by Steve Gorman, Daniel Trotta and Todd Eastham)

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