Thought Denver Broncos football was the official state sport of Colorado?

Nope.

Meet the men and women of pack burro racing.

It began as a distraction for overworked miners and evolved as a curiosity in mountain towns hoping to draw more visitors to summer festivals. But for a group of hard-core enthusiasts, it is a grueling competition against the mountains and other runners and an often exasperating struggle with “an animal not generally known for its cooperative nature,” said Hal Walter, a six-time champion from Westcliffe.

And it really is the official state sport of Colorado, so designated by the Legislature in 2012.

“You feel the fluid running style of the quadruped and become in sync with that animal. It’s just such a more dynamic experience than running can ever be,” said Walter, 53, a journalist who has written a book on the sport. “Running is like putting one foot in front of the other. You’ve got to manage a lot of other stuff with the burro.”

Walter will be in Colorado Springs on April 4, when he will speak about the sport at the showing of “Haulin’ Ass,” a film that follows him and two other competitors through a season of racing the one sport that can claim to be a Colorado original.

The first race was held in 1949 on a 23-mile course over 13,185-foot Mosquito Pass from Leadville to Fairplay. The rules were and remain simple: A runner and donkey on a leash race against other teams, and whipping the animals is not allowed.

For three weeks in late summer, runners and their donkeys converge on central Colorado for the Triple Crown of burro racing, held this year July 28 in Fairplay, Aug. 4 in Leadville and Aug. 11 in Buena Vista. The film covers the 2009 running of these three races.

It is, says the narrator, “a story about a bunch of bull moose-looney athletes, their critters and these tribesmen that suit up for a poor man’s Triple Crown, where the jockeys work as hard as the equines.”

Donkeys are related to horses but, as the movie shows, they’re a lot tougher to work with. On any given day, a donkey might be fast and leading the runner or be as stubborn as an, well, you get the picture.

As the runners plod high into the tundra and talus of the Mosquito Range, it’s hard to tell who is more exhausted, human or donkey.

Walter is doomed to lose to Buena Vista’s Bobby Lewis in all three races, as his burro Laredo refuses to pass Lewis’ burro Wellstone, and he drags his burro across the finish line to second place. Maybe it’s because Laredo is Wellstone’s father, he said.

Training the donkeys is the toughest part, and Walter has had eight over 33 years of racing. When their racing careers are over, he keeps some burros as pets and gives away or sells others. Runners develop an empathy for these animals and their ability to navigate terrain few other pack animals could tackle.

Training is key in what is a very competitive sport. While there are plenty of kids and grizzled old men with long beards in the races, publicity is bringing more and better-trained runners to the sport.

“It’s been interesting to see, for somebody who’s been with it as long as I have. It’s sort of like seeing an evolution of a sport,” Walter said.

But it’s still a friendly competition among a small cadre of people united in their love of running, the mountains and the animals.

Curtis Imrie of Buena Vista, one of the other racers featured in the movie, has been racing donkeys for 40 years. He learned the sport from a veteran who saw him jogging on the road and said, “Boy, you have the legs, but you don’t have the ass,” he says in the film.

In his 60s, he still runs and finished fourth in the grueling Fairplay race last summer. He enjoys the “pretty gnarly attitude” of his cohorts in the sport.

“I’m proud to be involved with this tribe of donkey chasers, wrestlers,” he says at the end of the movie. “I’m happy to have them in my life and to help people learn a donkey is more than a jackass.”