What book inspired Cheryl's journey? Where did Cheryl first encounter this book?

Cheryl remembers when she first looked at the book that inspired her trip, titled The Pacific Crest Trail, Volume I: California. She was in Sioux Falls, South Dakota with her friend, Aimee, to pick up her truck. It was while waiting in line that she first saw the book, although she didn't give much thought to it then.