GO HOME, ARON, THE VOICE SAYS. PUT YOUR SKIS ON, ENJOY THE RIDE DOWN. YOU'VE CLIMBED 58 OF THESE FOURTEENERS—YOU DON'T NEED ANOTHER. C'MON, LET IT BE.

It's a cold March morning, and I'm standing at 13,800 feet on the snow-filled saddle between the north and south summits of 14,083-foot Mount Eolus, in the Needles of southwestern Colorado's San Juan Mountains. Squinting behind my darkest sunglasses against the high-altitude sun, I scan for a single piece of evidence that might disprove the illusion that I am the only human within 50 miles. But I seem to have the planet to myself—or at least the hundreds of peaks and ridges in Colorado's largest wilderness, an exquisite nowhere that includes 28 of the 100 highest mountains in the 3,000-mile Rocky Mountain chain.

Of all those ridgelines, I'm staring ahead at one: the Catwalk, an exposed, snow-riddled knife-edge that separates me from the final 300 vertical feet of a seven-winter mountaineering project. In 1997, I set out to climb all of Colorado's 14,000-foot peaks, alone and in winter, and Eolus is my last. Now, after three strenuous days on the approach, I stand just an hour from the summit and consider calling the whole thing off.

But then another voice interrupts: This is the last mountain. Conditions are good, the weather's good; you're just intimidated. Do what you do. Climb.

I inch forward. A third of the way out, I pause at a spot where a lonesome rocky knuckle disappears below a double-edged cornice stretching ahead for 50 yards. True to the mountain's namesake, Aeolus—ancient Greek custodian of the four winds—swirling, winter-long gusts have built the snow into cantilevered curls that droop under their own weight like the furling wings of an albino manta ray. I'll have to trace the exact crest of the underlying rocks, mindful that with each step one of my cramponed ski boots could sink unexpectedly and throw me catastrophically off balance. A mistake could dislodge the entire snowpack, sending me and several tons of snow crashing down a thousand feet.

Looking back toward the summit of North Eolus, I can see an enormous cross of snow set in the pink granite. Back in the summer of 1999, I watched from a nearby valley as a rescue helicopter hovered above that cross, dangling a haul line down to the body of a fallen mountaineer. Blocking out visions of a helicopter short-haul involving my own lifeless form, I advance nearly doubled over, probing with my ice ax in my left hand as I balance my weight on the ski pole clamped in the prosthetic gripper I wear on my handless right arm. When the ax strikes buried rock, I move, reassured. When it doesn't, I'm all too aware that my next step could be a fatal one.