It’s tough getting into the winter sledding state of mind when it’s 80 degrees outside, most of the leaves are still on the trees and I’m dripping with sweat, even in shorts and a T-shirt. But as I hoof it up the west side of Prickly Mountain in Warren, the sledding potential of this wooded glade comes into mental focus. Soon, it’s clear why Whitney Phillips, the 28-year-old president of the Mad River Rocket sled company and an extreme-sports enthusiast, dragged me up here: to show off a deep, 0.4-mile-long half-pipe naturally carved into the side of the mountain.

“This is the gulley,” Phillips announces proudly, as though he had dug it himself over his summer vacation. “When it gets buried in snow, this is where it’s at. This is the fun stuff.”

Indeed. It doesn’t take much effort to imagine how “freesledding” junkies — a relatively new winter sport linked to the short, maneuverable Rocket sleds — will put this terrain to good use once it’s blanketed with several feet of snow. There are plenty of rock ledges and cliffs to launch 360s, back flips and barrel rolls. Downed logs as long as tour buses jut out of the ground at odd angles, facilitating jumps and rail riding. The standing trees are spaced tightly enough to keep the runs exciting, but airy enough to let sledders schuss to the bottom of the mountain without getting clotheslined by low-hanging branches.

But this winter playground-to-be, located on 250 acres of private forestland in Warren, wasn’t the handiwork of excavators, bulldozers and log skidders; Mother Nature did most of the heavy lifting. And architect Dave Sellers, landowner and founder of the Mad River Rocket Company, intends to keep it that way — with a little help from a local forester.

Prickly Mountain will soon be the home of the new Mad River Rocket Sled Park, a prototype sledding hill for testing new products, shooting promotional videos, and offering guided sled tours to schools, teams and outing clubs — all the while showcasing eco-friendly forestry and low-impact wilderness recreation. In the next few weeks, a number of trees, stumps and downed timber will be logged on the property, but only those designated by a state-certified forester. Nothing will be removed from the land for the sole purpose of creating sled trails.

“It’s not going to look anything like a ski trail,” Phillips insists. “If you were above this in a helicopter, you wouldn’t even see it.”

Actually, the idea of turning this swath of forestland into a sled park was sort of an afterthought. Sellers, 69, is one of a handful of architects from the Yale School of Architecture who came to the Mad River Valley in the mid-1960s to show their stuff. The young architects — many of whom are connected to the nearby Yestermorrow Design-Build School — collectively purchased about 450 acres of forestland and farmland in the area, at prices that would make today’s real estate investors envious.

For years, this patch of forest has been included in Vermont’s Use Value Appraisal Program, which allows landowners like Sellers to lower their property tax bills in exchange for keeping their land undeveloped. To participate, a state-certified forester must inspect the land every 10 years and prescribe a forest resource management plan.

But unlike woodlands that are managed primarily for timber harvesting, land in this program is evaluated according to all of its natural assets, including soil and water quality, wildlife habitat, recreational potential, even aesthetic appeal. When a forester recently determined that some of the older, infested and dead trees would have to go, the idea of the natural-terrain sled park was born.

In one respect, the new sled hill makes official what Mad River Rocket has been doing all along. Sellers first invented the high-tech sled in 1987 so that kids already riding down Prickly Mountain could do so without crashing into the trees. The Rocket soon caught on among older backcountry enthusiasts, who were drawn to the sled’s maneuverability, comfort, durability and light weight — the polyethylene body is 47 inches long and weighs just 6 pounds.

It’s harder to imagine that demographic getting into Rocket-riding position, however. Unlike a traditional sled or toboggan that you sit or lie on, a Rocket rider kneels down and straps in — hence the company’s slogan, “Get on your knees!” — leaving the hands free for steering, balancing and braking. The sledder can then carve sharp S-turns like a snowboarder, while ducking under obstacles that would fell a taller target.

Sound athletic? There’s more. Interestingly, it’s the Rocket’s consumers — not its makers — who have explored the sled’s full potential. Several years ago, Phillips got a phone call from a couple of teenagers in Underhill. They asked if they could send him a video of them riding their Rocket sleds. The two-hour home movie, shot by Nathan Steinbauer and Isaac Fleming, featured the teens performing aerial stunts more commonly done by extreme snowboarders — back flips, 720s, barrel rolls, even jumping from one snow-covered rooftop to another.

Steinbauer and Fleming, who have since moved on to whiter pastures out West, still produce some of the best marketing footage used by the Mad River Rocket Company. Moreover, Phillips says that the popularity of YouTube has led to other teens producing similar videos, which have only boosted the Rocket’s international appeal.

“Nobody’s paying these kids to do it; they just do it,” Phillips notes. “Then I call them up and say, ‘Do you guys want some free sleds?’ And they’re like, ‘You’re damn right!’” As a result, Phillips has been able to phase out his national sales force in favor of 10, eight-member teams — from Alaska to California to Colorado to Vermont — who shoot most of the videos and spread the gospel about freesledding. This year, the company’s pre-season orders are up 15 percent over last year; the American-made sleds, made of 100 percent recycled plastic, are now being sold in Canada and Japan.

The Rocket’s increasing global popularity hasn’t diminished the company’s need for a home base, however: a spot nearby where Mad River Rocket’s sled teams can gather and shoot new promotional footage. During the upcoming season, the park will be open for limited use; only Rocket sleds will be allowed on the hill. When Prickly Mountain opens to the public in 2009, it will likely be restricted to organized groups and invited guests.

That said, Phillips emphasizes that the sled park idea isn’t driven entirely by self-interest. The long-term goal is to create a model for other environmentally friendly sled parks sans big-footprint lodges, clear-cut trails or high-speed lifts. Most of the wood logged this fall will be used for building mini warming huts and other modest improvements on the property. This winter, Phillips says they’ll use an environmentally friendlier snowmobile with a trailer attached to shuttle riders up to the top of the half-mile, 1211-vertical-foot slope. Eventually, he hopes to bring in an old VW Bug engine powered on veggie oil to run a small lift or rope tow.

Since the goal is to keep the park as close to nature as possible, that means no Snowcats or artificial snowmaking. “The cliffs are what I’m really stoked about,” Phillips says, eyeballing the steep hillside. “Now all we need is a lot of snow this year.”