It shows. On a recent sunny morning, the Prescott resident made quick work of the "Out From Under" boulder near Thumb Butte, deftly finding hand- and foot-holds to propel herself over the large rock.
Thornhill got into the sport at age five, when her mother took her on climbing excursions. Then, from age nine to 18, she participated in a climbing team in Bozeman, Mont., and later honed her skills as a student at Prescott College.
Even with all of her experience, though, Thornhill said climbing continues to challenge her.
"When I climb, I get scared almost every single time that I go up," she said as she donned her climbing shoes. "But I've spent many years learning how to harness that fear, and it puts me in a place mentally that I am just overjoyed and I feel very strong and capable."
It is that type of joy and fulfillment that local climbing enthusiast and filmmaker Titiana Shostak-Kinker hopes to capture in a new short movie that will focus exclusively on female climbers.
With the working title "On the Rocks," the film will feature about 10 local climbers.
"I've had this dream for over a decade to make an all-women's climbing film," Shostak-Kinker said.
After taking up rock-climbing in 1997, Shostak-Kinker said she began seeking out climbing movies, watching as many as she could find.
"A lot of them are based on adrenalin and ego," she said of the films that are currently available.
Shostak-Kinker set about to change that. Her film will be about "the joy that people - especially women - experience when they climb," she said.
The three main themes of the movie: Strength, beauty, and peace of mind.
Shostak-Kinker traces her love of the outdoors to her childhood. "I grew up in Vermont, and I spent a lot of time as a kid running in the woods," she said.
Then, when she attended Prescott College in the late 1990s, Shostak-Kinker took an introductory course in rock climbing and became enthralled with the sport.
Since then, she has climbed all over the world, traveling to Thailand, Mexico, Czech Republic, Germany, Italy, France, Nepal, and Canada.
Still, Shostak-Kinker said, Arizona climbing locales can stand up to the worldwide competition.
"Arizona has the best climbing," she said.
While most climbing locations around the world feature just one type of rock for climbing - sandstone, basalt, granite, quartzite, or limestone - Shostak-Kinker said Arizona offers all within just 80 miles or so.
And opportunities abound in the Prescott area. "Granite Mountain is my favorite place, and Thumb Butte is another big one," Shostak-Kinker said.
She took advantage of the variety in filming for "On the Rocks." The 30 hours of footage that she currently is editing includes sweeping views of climbers negotiating rocks in Chino Valley, Groom Creek, the Granite Dells, and Sedona.
"It's all local women, and local rock," Shostak-Kinker said.
To help pay for the production of the movie, Shostak-Kinker used Kickstarter, a fundraising platform for creative projects. On Tuesday, with four days to go in the campaign, 94 backers had pledged $4,415 toward the "On the Rocks" short film.
Shostak-Kinker expects the movie to be complete by about October, and she said a showing would take place this fall at The Raven Café in downtown Prescott.
The movie trailer, which is available online, immediately takes viewers directly into the climbing action.
With its vast views, the trailer not only showcases the skills of the climbers, but the breadth of the surroundings as well.
Shostak-Kinker said that was intentional. "I want to show the power of wilderness and nature," she said, noting that climbing "makes a person feel so small."
Along with the climbers who participated, Shostak-Kinker said a number of other local women also helped with the other tasks, such as filming, rigging and the Kickstarter campaign.
"Everyone involved was completely volunteer," Shostak-Kinker said.
In showing the beauty and grace of climbing, Shostak-Kinker said, "We hope to inspire young female athletes."