The squeak of a seatpost and the soft crunch of 29" tires were a welcome distraction from the scorching, dusty silence. I was on a long backcountry run earlier this summer, on a sweltering afternoon, and hadn’t seen a soul since I left the trailhead near Fairfax in Marin County, California.

Michael Popov in Death Valley Michael Popov in Death Valley

The mountain biker passed slowly on the rock-studded jeep trail, grunting a hello as he powered past. He was enormous, with Promethean thighs and calves the size of muskmelons. Even huger was his pack, a full 70-liter monster, loaded up expedition-style, with a pair of La Sportiva trail running shoes strapped tightly to the lid.

No one carries a pack that big, I thought. No one heads out this far in this heat, without being an adventure racer. And there is only one adventure racer in Northern California the size of an NFL linebacker.

“Michael,” I shouted, and just one month before he would die, cooked in his own skin on a 123-degree day in Death Valley, Michael Popov stopped his bike, turned around and said, “Gordon! I thought that was you! What are you doing out here?”

Michael Popov was as physically imposing as his endurance exploits. Standing well over six feet and slabbed with muscle, he looked—and sounded—like Ivan Drago, the stony Russian boxer played by Dolph Lundgren in Rocky IV. But like many big men, Popov’s intimidating frame hid a friendliness and gentle nature that endeared the Walnut Creek resident to the adventure and endurance communities of Northern California.

We caught up on gossip and compared each other’s routes for a while before he set off up a long slope. I would catch up with him later, and we leap-frogged through much of the next hour on the ridgelines perched above West Marin. When I saw him last, shortly before I closed my run loop to head home, he was resting in the shade of a dwarf cypress, sweating heavily.

“Great to see you, Michael. You all set for water?” I asked the Russian native, who grinned back.

“I have some, thanks, and I may filter some later,” Michael replied, and we committed an awkward fistbump-handshake-hug before I trotted off, not knowing that this man, the strongest athlete I knew, the holder of some of the most brutal endurance running records in the West, would be dead before summer’s end.

SARAH SPELT IS HOLDING up admirably well for someone who just lost a person she describes as, “A partner. That’s what we were. Partner in adventure, professional partner, romantic partner...” she tailed off, caught on the degree to which her life was entwined with Popov’s.

Spelt, 53, a co-founder of Pacific Coast Trail Runs, was with Popov last week on a reconnaissance trip to Death Valley to scout a 100-mile ultramarathon race the two planned to stage next year.

On Tuesday, August 7, they entered Death Valley from the north, passing through Bishop and Furnace Creek before leaving Badwater Road to head south along West Side Road.

After driving into the heart of the Death Valley basin, Popov turned to Spelt and said, “So, I may regret it, but I’m going to run from West Side Road to Badwater today. You can drop me off and drive to Badwater and pick me up.”

According to Spelt, Popov had never sprung an adventure on her like this. He was known to be a meticulous planner, and while he had a backpack and running gear, he had only a cell phone as an emergency measure.

“We had always planned our days, runs and hikes together, but not this time,” noted Spelt. “And I think now that it was because he knew it was risky, he was nervous about it, and that he knew I might object."

METICULOUS PLANNING IS AS essential as fitness for the exploits that Popov took on—feats of endurance that shattered records and left many speechless. In 2007, he crushed the record for the fastest unsupported traverse of the John Muir Trail, taking only four days and five hours to run from Whitney Portal to Yosemite Valley (a record since broken). In September 2011, Popov took on the Tahoe Rim Trail, also unsupported, and circumnavigated one of the world’s most scenic trail network, covering 165 miles in a staggeringly fast 63 hours, 54 minutes—more than 20 hours quicker than the previous record.

Expeditions like this are enormously taxing, nerve-fraying, and present mental and physical challenges unimaginable to recreational trail runners. The amount of planning and hard-won experience needed just to consider endeavors like this are tackled by only a handful of men and women—like Marshall Ulrich, Brett Maune and Sue Johnston. Even the world’s greatest trail runner, Killian Jornet, took on the Tahoe Rim trail record only with the substantial help of sponsors and supporters.

And yet, on that Tuesday in August, in the heart of the summer, Popov set off southeast from West Side Road, intent on running cross-country to reach the paved Badwater Road, which he and Spelt thought to be roughly 10 kilometers away. If he was nervous, he had to have been reassured by the looming ramparts of rock shimmering just across the valley.

After stopping once at a crossing that proved too overgrown to traverse, the couple headed farther south, to a speck on the road called Shorty’s Grave. After some more debate about the route, Popov decided to head across the basin to an easily-identifiable black rock outcropping visible across the desert.

“Do you feel safe doing this?” asked Spelt, something she said she had never before asked him, or felt the need to ask him.

According to Spelt, “He grabbed me and hugged me and said, ‘No—don’t start your worry-watch for three hours.’”

Spelt loaded four water bottles with ice, water, and Nuun, snapped a few pictures of her partner, and watched him run out into the desert. The time was approximately 2:00 p.m., and the temperature was 123 degrees.

“That’s the last time I saw him alive,” said Spelt.

ACCORDING TO DR. BEN JONES, the Lone Pine physician better known as Badwater Ben Jones, who would have the difficult task of performing the autopsy on Popov’s body, the terrain at that point in Death Valley isn’t just scorchingly hot—it is unpredictable, and nasty.

“There is rainfall in Death Valley, and in that area—Lake Manly—there is subsurface moisture that can make you posthole up to your knees.” Jones suspects that Popov found the footing to be so bad that he contoured southeast on a diagonal to avoid it.

Jones also notes that even experienced adventurers like Popov can underestimate the intensity of the heat, and the amount of water needed. Badwater Jones, who for years held training camps for prospective competitors in the Badwater Ultramarathon, estimates that at least two to three weeks of heat acclimatization are needed for the race, and that runners need to drink at least two to three liters of water per hour to maintain hydration.

Popov, conqueror of so many epics, bet his life that he could cross a few miles of desert.

He was carrying less than two liters.

THE SOUTHERN DIVERSION MEANT Popov would ultimately travel an estimated 10 miles. The crossing took him only approximately two and a half hours, and like so many other adventures he took on, he made it.

Few cars are found on Badwater Road in the middle of summer, but around 4:30 p.m. several of them stopped when they saw Michael Popov’s form lying on the side of the asphalt, six miles south of Badwater itself. One good samaritan drove north to the town, found satellite phone reception, and called the authorities.

Others stayed with Popov, who was conscious but delirious and combative. When his condition worsened, they performed CPR. An ambulance crew arrived and took over resuscitation efforts. They called in a Life Flight helicopter, and that crew attempted to shock his heart into beating.

All efforts failed.

Dr. Jones said that the cause of death was “Heat-related, including asphyxiation due to pulmonary hemorrhaging.”

In about two and a half hours, the desert had torched the life from Michael Popov. All four of his water bottles were drained. “He didn’t have enough water to last him much more than an hour,” noted Jones, who also said that Popov, who had crewed at the Badwater Ultramarathon, was the closest acquaintance on whom he’s ever had to conduct an autopsy.

Sarah Spelt, who has spent the past week juggling the hundreds of responsibilities of the bereaved in the social media age, reflected on her loss, and on the meaning of Michael’s death.

“Losing one’s true love should be unbearable, but when you love someone as much as I did Misha, it somehow becomes more bearable.”

Some may fault Popov, or even, somehow, Spelt, for Michael’s last run. The temperature was simply too great, and his fluid reserves too thin, to attempt the adventure. But both of them respected the desert greatly, and both were familiar with Death Valley. Michael Popov simply was guilty of a fatal miscalculation, perhaps brought about by his unsurpassed record of endurance successes and fateful strength.

Gordon Wright is an adventure racer and the president of Outside PR & Sportsmarketing, based in Sausalito, California.