“My dad said I could have stayed on our farm in Minnesota and worked, but I liked it better in the mountains,’’ Highum said.

This was a on recent day and Highum, 70, and a small posse of other riders on horseback were fanning into the Beaverhead Mountains, a sub-range of the Bitterroots that divide southwest Montana from Idaho.

The day was cool but clear as Highum, a retired ethanol plant chief financial officer who lives in Evansville, Minn., angled Bo, his quarter-horse gelding, into a mountain drainage, weaving as he did among languid creeks, squishy grass and statuesque lodgepole pines.

At another time, Highum or horsemen like him might have been hunting elk in these mountains, scabbards swinging from their saddles. The big animals summer here before migrating in autumn over the Continental Divide to Idaho, where they bask on mountainsides bared of snow by the winter sun.

Instead, Highum and the other riders, seven in all from Minnesota, were part of an American ritual as old as the nation itself: fall roundup, during which cattle that have spent the summer chomping mountain grasses are gathered and driven to lower country, where they over-winter.

Romanticized in American literature since just after the Civil War, roundups can test the mettle of cowboys and their horses, who must brave the weather, badger holes, fallen trees, uncooperative bovines and, even today in the Beaverheads, wolves, bears and mountain lions.

A challenge of the current undertaking is that some of the approximately 600 animals Highum and the other riders are searching for don’t want to be found. Another is that the cattle are spread over 13,000 acres of U.S. Forest Service leases.

So it’s hide-and-seek, and the dozen or more cowboys and one cowgirl on this roundup — including ranch owners Clay and Dean Peterson — rise before sunup and share breakfast in a mountain cabin before saddling their horses, loading them into trailers and pulling the heavy, rattling rigs behind vintage pickups over washboard roads to higher elevations. There, amid temperatures in the 20s and 30s, whether beneath clear skies or while being pelted by snow, and flanked by cow dogs eager to scour the mountains, the horses are unloaded and the riders pull themselves into cold saddles, finding their stirrups with pointed boots.

The process is reversed 10 or so hours later as sundown nears, when the riders return to the cabin and unsaddle their horses, allowing them to graze and rest in the coming cold night.

“No one stays up long after supper,’’ said Mike Krause, a building maintenance contractor from South Haven, Minn. “You get into bed as quickly as you can.’’

• • •

A cutting-horse competitor in Minnesota, Krause, 65, like Highum, has traveled to the Peterson ranch for decades, usually trailering a horse or two as he drives west in late September or early October. The roundup’s unique alloy of physical exertion, unparalleled scenery and challenging riding prove irresistible, he says, as autumn days shorten.

Bosses of this roundup are the Petersons, Clay and Dean, whose great-grandfather, Sam, homesteaded in the Big Hole after landing in Montana from Sweden when he was a teenager. Sam Peterson made a living buying cattle in Idaho in the fall and driving them over the Continental Divide to his home place, where he’d fatten the animals on hay and sell them in spring.

“At the time he believed the environment of this valley was too harsh to have a cow-calf operation,’’ Clay said.

Independent thinkers, the Peterson brothers work hard, laugh easily and lean conservative politically. Clay, 49, and his wife Stephanie, 47, have three children: Morgan, 23, who just finished college, majoring in pre-med; Jordan, 21, a senior at the U.S. Air Force Academy on a career track to fly fighter jets; and Luke, a student in Missoula wanting eventually to return to the ranch.

Dean, 52, and his wife, Dianna, are parents of Alfred, 17, Malcolm, 15, and Jon, 12. Already skilled horsemen, the older boys attend high school 60 miles away in Dillon, Mont., population 4,264. During the school year, when Alfred and Malcolm are involved in sports and other activities, they and Dianna rent an apartment in town.

“It’s the only option.’’ Dean said. “Otherwise the school bus ride is an hour long each way.’’

On this day, Dave Buck of Hall, Mont., along with Clay and I split up from the other riders, among them Minnesotans Dave Hamilton, 65, a banker from Stillwater; Justin Klejeski, 34, a Silver Lake farrier; Jason Foss, 35, a veterinarian from Cokato; and Emma Koeberl, 28, a Princeton office manager.

Each of us wore chaps to protect our legs and cowboy hats to keep the wind and sun off our faces.

Pressing our horses upslope, Clay, Dave and I began a long, circuitous loop in search of three missing cow-calf pairs and a Hereford bull. Climbing higher and higher beneath a cobalt sky, we leveled off in a meadow ringed by quaking aspens aflame in seasonal yellows and golds.

These mountains are Clay’s backyard, and Dean’s, and they know them well. They also know where recalcitrant cows and calves are likely to hang out, and Hereford bulls, too. If we’re lucky, Clay says, we’ll find the animals and they’ll push easily to the valley below, where in coming days we’ll sort the cows from their mothers, vaccinate or “doctor’’ the younger animals and castrate the bull calves.

“Our cattle are black Angus, which are best for our kind of weather, but we mix some Hereford into our breeding for hybrid vigor,’’ Clay said. “Our cattle are graded when we sell them, for marbling and other factors, and we don’t want too much Hereford in the mix.’’

• • •

The roundup’s even more ambitious and arduous antecedent, the cattle drive, peaked in about 1880, when Brahmans and longhorns were driven by the thousands out of Texas to feed gold miners as far away as California.

Dave Hamilton, the Stillwater banker, Mike Krause and I were thankful we didn’t have to push cattle from Fort Worth to San Francisco. Or, really, to ride any more at all. At day’s end, we shared a small log cabin that harkened to a time long past, and on our final night in camp, we crawled into our sleeping bags enthusiastically.

By then, all but a handful of the Petersons’ cow-calf pairs had been found, and the stragglers, Clay said, likely would show up with the first heavy snow.

Dave doused the cabin’s lone bare light bulb.

Then he said, “Every year at the end of roundup I say this will be my last one. Especially when it’s rained and snowed every day, and been cold.’’

Mike let this sit awhile.

Then he said, “You’ll be back. We all will.’’

And we fell asleep.