On a February morning in 2006, the ground in the Kabetogama State Forest of northern Minnesota was frozen and dead, a chalky medium that squeaked when I walked from the car pushing my bike. The air was sharp, elemental and shrill, hurtful to breathe even through a mask.

It was predawn on the Arrowhead State Trail, a multi-use track that connects International Falls to the town of Tower more than 100 miles to the south. My hands ached from the cold, and my fingers went numb within minutes as I got on my bike to pedal into wilderness as desolate as the dark side of the moon.

The Arrowhead 135 Ultramarathon, Minnesota's most extreme endurance race, had just begun. One woman and 31 men set off with headlamps and bike lights ablaze in the still, silent woods outside International Falls.

"Keep spinning, warm the toes," a fellow racer shouted, his masked face frosty, his body thickly bundled in Gore-Tex and wool. "Can't wait for that sun to rise!" he said.

Neither could I. On the horizon, beyond the black arms and silhouettes of the forest, blue and gold light was seeping up to initiate Day 1 of the race.

As ultras go, the Arrowhead 135 is an odd event, more akin to an Alaskan sled-dog epic than a century bike ride or triathlon. The race, which kicks off its fourth annual trek Monday, requires competitors to combine athletic strength with survivalism, sending cyclists, trekkers and skiers solo and unsupported along the race's namesake 135-mile remote and rolling course.

The Ironman this is not. No one is in the woods to cheer. There are no water stops or hand-out energy gels. On the Arrowhead Trail, you haul all your own food and gear. You melt snow with fire to make water. You sleep, if need be, on the ground, a black sky above, stars pricking through, wolf prints in the woods out beyond your packed platform in the snow.

You are given 60 hours to complete the course via one chosen mode of transportation -- foot, ski or bicycle in the snow. You get a map at the start and follow a trail that fades in and out -- with forks and intersections mostly unmarked -- and a spinning compass needle as your sole guide.

Most racers never finish; 60 percent surrender somewhere along the route. Last year, when the temperature dropped to minus-35 degrees during the night, only 10 of the 46 starters crossed the finish line at a lodge on Lake Vermilion, 135 miles and many cold hours down the line.

Woods' beauty is top draw

During my race, the sun rose bright that first icy morning, bursting yellow and gold, rays skipping over the snow. The thin, still air had a temperature of 20 below zero, ice crystals floating like glitter.

I pedaled a bike custom-made for the snow, with 4-inch-wide tires and racks to carry gear. The trail, primarily a snowmobile route, was packed and solid for the first few miles of the race.

From a trailhead near International Falls, the course began with a prologue there-and-back leg west about 9 miles into the woods. I tagged the checkpoint intersection after an hour of motion, then turned around to pedal east and south to the inner reaches of the Kabetogama forest.

"It's like Alaska out here -- beautiful," said Matt Evingson, a physician's assistant from Duluth and winner of the inaugural Arrowhead 135 Ultramarathon in 2005. We were pedaling side by side, the treeless expanse of a frozen bog glowing gold in early-morning rays.

The natural beauty of the North Woods is a top draw for Arrowhead racers. Competitors come from as far away as Brazil and as nearby as Ely. Birch, pine and poplar trees make up most of the scenery, but frozen rivers, ravines, lakes, bogs, huge ridgelines, cliffs and slopes so steep I had to push my bike up them create a course of ever-changing Ice Age-era topography.

The farther you go, the harder the race becomes. The hills get bigger. The trail becomes more remote. You get cold and run low on food.

There are three bail-out points within the first 60 miles of the course, including two road intersections and the checkpoint cabin on Elephant Lake, which is the halfway mark. But head out from there and you face a remote leg with few roads and no civilization, on your own for another 60 miles in the frozen woods.

20-mile mistake

My race went well to Elephant Lake, my tires humming fast on snow for most of the day. I arrived by early evening, happy for a break. But after leaving the cabin with fellow racer Dave Simmons of Fargo, my luck took a literal turn for the worse: We missed a crucial dogleg and got lost.

It took about four hours and almost 20 miles to correct the mistake. We circled and searched for a trail back to the cabin, pushing our bikes alone under the night sky.

At 2 a.m., we staggered back across Elephant Lake, returning to the halfway point, where Simmons quit the race. After three hours of sleep, I rolled back onto the trail, determined to finish, watching for the elusive missed junction.

The day dawned bright and soon the air was above zero. I stuck with St. Cloud attorney Matthew Staehling and his partner for much of the morning, ticking off 30 miles by early afternoon.

We pedaled nonstop for an hour or more at a time, tires churning in loose snow. Maintaining momentum required constant cranking; a moment of coasting in snow brought the bikes to a halt.

The trail climbed and dropped, weaving around lakes, cresting a huge hill near Lake Vermilion. "Only 35 miles more," Staehling said at one point.

Twelve hours after leaving Elephant Lake, I was in a daze as I saw the finish line materialize out of the dark. It was Tuesday evening by then, and I was riding alone again under the stars.

I parked my bike and walked inside the cabin to finish, collapsing on a couch.

"Hey, you made it!" someone shouted. The room was hot and bright, people laughing, coffee cups steaming. I sat back and closed my eyes, out of the wind and savoring a rush of warmth -- finally.

Stephen Regenold is a Twin Cities writer and author of the syndicated column www.thegearjunkie.com.