Each year around the Fourth of July, in a vale in the Rocky Mountains, a scene from another century plays out. Dozens of rugged-looking men mill around an encampment. They tether their horses and mules to trees. They wear animal skins. And as they roast slabs of buffalo meat over a fire sparked with flint and steel, they share tips on how best to trap beavers and load a flintlock rifle. Who are these guys?

View Images Larry Hanson, 74, used to be a sonar technician in the U.S. Navy. At the national rendezvous and other AMM events—like this wilderness ride in Canton, Kansas—he’s a mule skinner.

They’re American mountain men—reenactors of the fur trade that flourished in North America from roughly 1800 to 1840. Like the better known reenactors of the Civil War, they’re dentists or lawyers or mailmen in real life. But for a week each year they shake off the yoke of civilization and return to a time when survival meant self-reliance.

View Images After riding 35 miles that day, Rik “Hawk” Hurt (standing) and three other reenactors rest as their horses graze in Lima, Montana. Riders and steeds alike have to be in top shape to follow the original trails of 19th-century Western mountain men such as Jedediah Smith.

Photographer David Burnett recently spent two years among them. He found “a welcoming bunch who are really curious about what it took to live before the conveniences of modern life. They love knowing the old stuff, the authentic stuff—things that are no longer taught. And they love to share that knowledge.”

Indeed, the American Mountain Men (AMM) association strives to preserve “the traditions and ways of this nation’s most fearless pioneers and daring explorers” and “share the fraternal concept to teach, share, and learn the skills needed and required to survive and live as the great American mountain men did.” For most reenactors, interest in the bygone era began at a young age.

View Images Scott Olsen is a dentist from Dillon, Montana. When he’s in mountain man mode, his camp name is Doc Ivory. Here Doc sets out with his dog, Ume, to check beaver traps in the icy creeks of Montana’s Ruby Valley.

View Images In Snowcrest Ranch, Montana, Doc Ivory stands next to a fresh beaver pelt that he’ll dry and preserve.

“When I grew up, I read books on Davy Crockett, Kit Carson, and Daniel Boone,” says Scott “Doc Ivory” Olsen, a dentist in Dillon, Montana, and a 25-year AMM member. “And I realized I’d been born too late.”

The Western fur trade began after the Lewis and Clark expedition of 1805–06. In 1825 the first annual trappers’ gathering was held near McKinnon, Wyoming. Called the Rendavouze Creek Rendezvous, it was a boisterous, multiday affair—a chance for mountain men to sell their furs, replenish their supplies, and socialize again after months alone in the wild.

View Images Mike “Tio Miguel” Morgan, now a trapper in Laurin, Montana, was a Navy captain for 30 years before joining the American Mountain Men.

The fur trade died out in the middle of the 19th century, as fashions changed and fur prices plunged. But in 1968 its legacy was revived. That’s when a man named Walt Hayward founded the AMM with six other avid outdoorsmen and history buffs.

Today it’s a nationwide organization, with local brigades and gatherings in each state and a national rendezvous each year. They all follow the same mountain man code. But regional differences matter, says Mike “Tio Miguel” Morgan, a trapper and ex-Navy captain who joined his friend Olsen’s Montana Brigade in 1998.

View Images At the national rendezvous in Lima Peaks, Montana, mountain men and women gather near Hans Asmussen’s tepee to sing 19th-century songs and tell stories about the region.

View Images Gail Asmussen helps run her husband Hans’s acupuncture practice when she’s not being a mountain woman.

“East of the Mississippi,” he says, “mountain men were called long hunters. They’d wear cloth and woolens. Out West, we emulate the fur trade as it existed in the Rocky Mountains. That means we wear hides and skins and learn Western skills”—how to skin a muskrat, ride a horse, throw a knife, pilot a bull boat.

Getting the gear right is its own challenge. “I tried to fit in,” says Burnett. “I ordered white cotton, double button-front britches, a shirt, and moccasins. But when I put it all on, I looked like Little Lord Fauntleroy. So I put everything in a plastic bucket, added red-brown dye, and let it sit for four days. When I took it out, it looked like a 19th-century tie-dye.”

View Images On a beaver-trapping expedition in Snowcrest Ranch, Montana, Richard “Spirit Horse Hunter” Ashburn shaves carefully using a 185-year-old straight razor.

View Images As twilight settles over Green River Lakes, Wyoming, Richard “Spirit Horse Hunter” Ashburn builds a fire in a shelter he erected. His campsite is about 50 miles northwest of Pinedale, near where many 19th-century rendezvous were held. Today the town is home to the Museum of the Mountain Man.

To join the AMM, a “pilgrim” needs a member to sponsor and mentor him through a score of requirements and a couple of levels: “bossloper” and “hiveranno.” But regardless of rank, the goal is always the same.

“We want to document history in as complete a way as we can,” says Morgan, “and pass along valuable, forgotten skills, so that future generations will have access to the past.”