In a series of photographs Katie Arnold took, she watches her father, ill with cancer, shrinking into himself at the same time her newborn daughter, looped into his arms or stretched out on the floor beside him, is daily gaining in size and strength. She experienced it then like the perpetual cycle of life playing out in devastating and visible margins.

On the heels of her father's passing in 2010, she was besieged with a sense of her own mortality, and how critically she needed to stay alive for her daughters, which fed into intense postpartum anxiety. She took to running, often on the near-memorized trail up Atalaya, close to her home in Santa Fe, to cope. And she began to run farther and faster—eventually going on to win ultramarathons, including last summer's Leadville 100. She writes about the nearly 10-year journey in her recently released memoir, Running Home.

"People love to talk about, 'You're running away from something'—and there are days when I'm running away from, like, grocery shopping. But way skewed in the other direction is that I'm running toward who I am," she says. "I'm running toward my real self, and my creativity and I'm running toward how I want to be a mother, showing my girls you can do things you didn't think were possible, and you can have those voices of doubt in your head and still prevail."

Running Home became the title, she says, because "that was the overarching feeling of what I was doing."

But she didn't know that when she started. She moved through it all, heading into the unfamiliar territory that lay on the far side of those tough months, not knowing how much of what followed would be even harder, or who she would learn how to become along the way. And that, she says now, was something of a gift.

"The unknowing is the fertile part," she says. "That's the part where there's growth, there's potential, and things align. To use a word that maybe people might balk at, it's a magical place. Things present themselves that if you're just using your rational mind you would be shut down to or go, 'No, I have to stay on my path.' Running is the thing, and it's also the metaphor. It's also the way I learned these truths, which is to go forward into the unknown, literally one step at a time."

In the book's opening pages, she's in the thick of the Jemez Mountain 50K, her first ultramarathon. Then it jumps back in chronology to piece together her childhood, her parents' divorce, and the 10K race her father signed her and her sister up for when they were children, an experience that taught her to appreciate suffering and its rewards.

Running became a personal outlet through college, one of the ways she got to know and celebrate her new independent life in a new town when she moved at age 23 to Santa Fe for a job with Outside Magazine, and how she learned to write—feeling a simultaneous flow of the world and words. (She's finally swapped the index cards for note-taking that she used to tuck in her sports bra for her phone's voice recorder.) That connection to her writing gives running a timelessness, she says: "No matter what happens with my running as a competitive runner, it will always be how I tell stories."

For now, she's still training, with more 50-mile and 100-mile races on her calendar.

What the races and her father's coming and going tie together is a sense of acceptance to combat the anxiety that had started to take over her life. As a runner, she routinely has to practice the wisdom that even the best preparation can't control every outcome. That transfers right over to what she knew, and couldn't know about her father, and what she learned and could say only after he was gone. How these pieces intertwined have come clear only in time and through the writing that went into this book. It's a rare privilege of time and space to give ourselves: to set out on a trail uncertain exactly where it will go.

"It can be years before we know what our path was," she says. "You can't rush the story. The story is playing out and you're living it; like you're in this circle, and it's only when you get to a certain point that you get the perspective to look back. And there's no ending, as I found in the book. The ending is actually the beginning. I think that's what makes it so amazing. It's just this thing that keeps spinning."

Katie Arnold: Running Home

6 pm Tuesday March 26. Free. Garcia Street Books, 376 Garcia St., 986-0151