A sunny, bluebird day — much better than a full day of wind and bitter cold in the high alpine. Sunglasses and a ball cap. Lots of snacks and water. A pack for storing layers to be shed. A single AirPod, leaving one ear open for communication.

When it comes time for bootpacking Keystone Resort’s avalanche terrain, these are all suggestions of Leslie Chasky.

“And prepare to sweat — a lot,” said the resort’s ski patrol supervisor.

Oh yes, there is a physical toll to this tried-and-true method of avalanche mitigation.

That much is clear by the pictures Keystone recently posted to its social media: patrollers stepping down a steep slope one boot in front of the other. Here and elsewhere across Colorado’s ski country, they might spend all morning and afternoon stomping through thigh-high snow.

“I’m exhausted just looking at the photos,” read one response to Keystone’s post.

“Now that’s a leg day!” read another.

And another: “I had never heard of this before, that’s amazing!”

Surely that commenter is not alone.

“I’d guess most of the general public that skis our avalanche terrain in the heart of the season has no idea that a process like this happens,” Chasky said.

The process happens early in the season, as weak layers of snow notoriously blanket Colorado’s mountains.

“The ski areas in Colorado, especially the big ones, they’re in what we call Class A avalanche areas,” said Ethan Greene, director of Colorado Avalanche Information Center. “They have very active avalanche slopes; that’s what people like to ski. But people don’t see avalanches at those places, because patrollers are really good at what they do.”

Patrollers assess slopes for safe stepping — for bootpacking, as a 2008 paper explained. Prepared for the International Snow Science Workshop, the paper was out of Aspen Highlands, where patrollers and hearty volunteers for decades have offered their bootpacking services for a season pass.

“Approximately 4,500 man hours are necessary to complete the job,” according to the paper, “and of course that varies with weather and snow cover properties.”

The properties of concern: “People call it sugar snow, because it’s really coarse,” Greene said.

Colorado’s early snow tends to fall “shallow” and faceted,” the Aspen paper described, “with inherent cohesion issues.” It is far from a guarantee that future snow will hold firm.

Unless, perhaps, the early layers are stomped.

The idea is “disturbance,” explained Reed Ryan, Copper Mountain Resort’s snow safety supervisor. Think of shoveling your driveway, he said. “When you put it on the side of your driveway, it’s no longer that powdery snow. It recenters as a much harder version.”

Bootpacking results in a grid of holes, a slope appearing like honeycomb.

“Think about if you’ve ever seen somebody put in a concrete foundation with pillars,” Ryan said. “New snow will kind of blow into those holes. It just creates a much better surface for bonding moving forward for new snow to attach to.”

Ryan called Copper Mountain’s bootpacking program “probably the most robust program that we’ve ever had.” In a years-long tradition similar to Aspen Highlands, volunteers with expert skiing abilities and cautionary beacons, shovels and probes have spent long days bootpacking.

They might be earning more than a season pass. It could be said they are earning turns for skiers to come. That’s the intent of bootpacking — stabilizing slopes so they can open for business as early as possible.

It’s not like explosives used for clearing avalanche-prone snow above Colorado’s highways. “The ski areas use explosives too,” Greene noted, “but it’s very different when you’re trying to create a product for customers that involves (keeping) snow on a steep slope.”

At Loveland Ski Area, explosives are used across more distant, less accessible slopes, said Eric Mikolajczak, snow safety supervisor. But if his team can safely reach terrain, they’ll be bootpacking — no matter any dread.

“I’d be lying if I said there wasn’t any,” he said. “It does take a lot of endurance and energy to work your way a couple hundred feet down a slope sidestepping the entire day.”

Said Chaskey at Keystone: “We call it Type 2 fun.”

She described patrollers walking in lines about a meter apart, steadily stepping down the mountainside through snow that might be piled above the knee. “The excitement and anticipation of the task at hand quickly turns into an elevated heart rate and a bead of sweat running down your back,” Chaskey said.

For any onlooker saying there’s got to be a better way? “I’d say they’re probably right,” Mikolajczak said, “but they might not be in touch with our operations as we are.”

Another way is by terrain roller, “which is operated by a winch cat,” Ryan said. “So obviously you need a snowcat to operate it, and you need a place where you can put a snowcat. You can’t always do that.”

And so the old-fashioned way. The hard way.

And the most rewarding, Mikolajczak said.

“Seeing people have fun and enjoy the mountain for something we put a lot of work into, it’s a pretty cool feeling,” he said.