By Andrew Travers, Aspen Times After his historic free-climb ascent of the El Capitan’s Dawn Wall in Yosemite National Park in early 2015, Tommy Caldwell stared down a nearly as daunting challenge: a blank page. To write his memoir, published last year as “The Push,” Caldwell used the same tools he’d used as a climber to revolutionize his sport and accomplish the seemingly impossible. “With climbing, I’m not super naturally talented physically and I’m kind of in the same boat intellectually,” Caldwell, who will open the Winter Words author series Jan.