Tommy Caldwell on the middle of the Dawn Wall, the hardest section of the climb.

(Brett Lowell/Big Up Productions)

The world watched in January 2015 as rock climbers Tommy Caldwell and Kevin Jorgeson scaled the smoothest part of the 3,000-foot tall El Capitan rock in Yosemite National Park. The two became the first ever to free-climb the Dawn Wall. Their feat is now the subject of a new documentary from Boulder-based Sender Films, called "The Dawn Wall." Filmmaker Josh Lowell and Caldwell talked to Colorado Matters about the accomplishment and the film.