"HOW MANY OF YOU are running your first ultra today?" asks Wendell Doman, the event coordinator at California's Carmel Valley Trail Run.

A handful of us meekly raise our hands, and the crowd of about 170 fellow runners—a mix of 8K, 19K, 25K, and 50K racers—offers a warm cheer.

"Good luck to you, and have fun," says Doman. "This is one of the hardest courses we offer." I look up at the 5,000-foot Santa Lucia Mountains, then over at my two-woman support crew—wife, Christian, and nine-month-old daughter, Olive. They're waiting for my estimated finish time so they know how many hours they have to kill while I try my latest incomprehensible stunt.

"Maybe come back in six hours instead of five?" I offer. Christian glances at me with equal parts pity, bewilderment, and halfhearted tolerance. I know this look. If it were accompanied by words, it would say, "Tell me again why the hell you're doing this … sweetie."

The race begins, leaving me with a lot of time to ponder the answer. Why am I doing this?

I have always been hooked by the simplicity of running. Put on shoes. Run. No expensive purchases or equipment maintenance necessary. Over time, running without a goal—known as jogging—wasn't enough, and for eight years my wife has supported my strange quest to raise the bar. It began with a couple of half marathons, a road marathon, and, finally, a few rugged trail mara­thons. I was never a serious competitor, but I finished, and after every race I was haunted by the same question: Could I go any further?

The logical next step was the 50K. At 31 miles, it's the starter's ultra, the gateway drug to long-distance addiction. I figured I'd simply adapt the marathon training plan I'd always used: regular weekday runs of three to seven miles, Saturdays off, and one progressively longer run every Sunday. To carve out training time, I'd take Olive with me, pushing her in a BOB stroller. She'd sleep; Christian would sleep in. Win-win. It all went perfectly until, late in my training, I made a naive calculation. Since I was pushing a stroller that was increasing in weight each week, maybe my long runs didn't have to be quite as, well, long.

So I'm not exactly prepared as we set off for the race. Within 300 yards, the course takes a right turn and ascends 900 feet up the valley floor, followed by a brutally steep downhill. All told, the race includes 8,600 feet of elevation gain over two laps, which means that as the 25K racers are trading war stories and high-fiving at the finish, I'm stocking up on energy gels and steeling myself to go again.

I see only three other runners during the next three hours. I?gobble salt tablets like peanuts to combat calf cramps, and walk backwards down one hill to alleviate the pounding. But mostly I'm in a groove, just planting one foot in front of the other. And that sensation is really why I run. I've tried meditation for years, but the closest I've come to Zen clarity is while running. The longer I go, the closer I get. Thoughts are gradually stripped away, like the chaotic layers of paint on a Jackson Pollock, until all that's left is a blank canvas and the things that really matter. Family. Wife. Child. Salt.

I shouldn't need six hours of exhaustion to realize what's important, but, hey, it works. And the epiphanies are addictive.