I'm betting they were WALKING along the ridge. It's amazing how many people don't think to CRAWL on ridges. Crawling virtually eliminates the risk of a fall because your center of gravity is so close to the ground, and you have four points of contact with the ground (ridge surface) rather than just two. I've seen photos of people walking totally upright on ridges. They're a fall ready to happen at any instant. Think, people.