Bryon Amo came riding along behind the Snow Dog, smiling as he maneuvered the machine through the woods at Hartley Park in Duluth.

The Snow Dog looks like a small snowmobile with no skis or seat. It’s essentially just the engine and the track, and it’s geared-down for muscle yet small enough to be maneuverable in thick woods.

The track is only 20 inches wide, but the unit is powerful enough with 13 1/2 horsepower to pull Amo. He was steering with handlebars while standing on a trail-grooming drag pulled behind the Snow Dog. It’s that drag that leaves a packed, corduroy-rippled trail for a multitude of users - fat bikers, hikers, dog walkers, trail runners and more.

“These trails are used by so many people doing different things. And this is giving us such a better experience,’’ Amo said during a break.

The Snow Dog "is letting us get into places we couldn’t get to before with a snowmobile,’’ Amo said. “And we can move it around easier… It’s 350 pounds so a couple guys can pick it up and put it in the back of a truck or slide it into a van.”

The units cost just under $4,000.

Amo is one of a group of volunteers, called the Hartley Snow Dogs, who have been grooming about eight miles of trail in the giant, heavily wooded park since the unit arrived in December. It’s the first year it’s been in use and, just last week, a second unit arrived, to be run by the Lester Snow Dogs volunteers. That will add more than 10 miles to the groomed trails in the area of Lester Park and Hawk Ridge.

“This is so nice to ride on,’’ said Sheila Amo, who was pedaling her fat bike down the packed and smoothed track her husband had groomed.

Daily dog walker Jeff Lyon, who lives near Hartley, agreed.

“It was hard to navigate'' walking on the icy, pitted trail before the groomer came around, Lyon said with his three dogs in tow. “Now it’s pretty nice. I use it every day.”

Hiker Sally Maxwell of Duluth said she used the groomed trail to take a walking break from babysitting her grandson.

“It’s wonderful to have it groomed,’’ she noted.

Step off the packed trail, however, and you'd sink up to your knees or higher; the snow was more than two feet deep, and that was before this weekend's snowstorm.

The Snow Dog allows grooming on trials that were too narrow, too steep or inaccessible for groomers pulled by traditional snowmobiles, said Eric Larson, an avid fat-bike rider who helped organize the purchase of the Snow Dog units through COGGS, Cyclists of Gitchee Gumee Shores, the Duluth-based off-road bicycle group. Larson spearhead a fundraiser that raised more than $6,400 for the groomers in just two weeks — mostly contributions from fat bikers.

“The key to a hardened trail is to first break down the snow crystal, and that’s what the track does, and then pack it and form it,’’ Larson said.

“When this track sets up, it’s absolutely perfect'' for fat bikes or feet, said Larson, an avid cyclist and fat bike owner. (There are more than a dozen bikes in Larson’s garage, he noted, including a few fat bikes, for him and his family.)

After most snowfalls, volunteers run the groomer, usually in the evening. It takes about 2½ hours to groom the trails at Hartley, Amo noted. After sitting over a cold night, the trails usually are hard-set by morning.

If it’s cold, near or below zero, trails generally hold up well. But if it warms into the upper 20s or above freezing, trails can quickly become soft. If people keep using them they become, like Swiss cheese, pocked with craters. Just like woodland trails should be avoided in snowless months after rains when they are muddy and prone to erosion, winter trails should be avoided when it’s warm or right after a big snow.

While the groomers are the brainchild of the fast-growing local fat-bike community, Larson said the bikers recognize that hikers, runners and dog walkers were on local trails first. He said a little patience and courtesy will allow all users to enjoy the same trails.

“The key, for everyone’s experience, is for everyone to wait until after it’s groomed and after it sets up,” Larson said. “Nobody wants a trail that's full of post holes and ruts. It’s asking for an injury... And it’s just not fun to ride or walk or run on a trail like that.”

The fat bike trail systems at Hartley and Lester are separate from the cross country ski system that’s also groomed by a large tractor-groomer. It’s also in addition to other bike trails that had already been groomed using a snowmobile pulling a drag groomer.

For more information on the Hartley Snow Dogs, call Eric Larson at 218-393-0757. For more information on the Lester volunteer grooming group, call Grant Harrison at 785-218-4393.

"We're trying to reach out to the runners. dog walkers and everyone who uses these trails to get involve in the grooming effort and keeping these tails open and in good shape,'' Harrison said.