He calls this ledge a "sidewalk".
I wish the Native Americans of old (probably of the Fremont culture in this area) hadn't liked heights so much. They often built their homes in cliffy spots. Here are the ruins of a 1000 year old pit house, situated at least a couple of hundred feet above the Nine Mile Valley floor:
Their choice was logical, though. The height gave them a good view in all accessible directions. If enemies attacked, the pit house dwellers would have had plenty of warning.
Up above the old dwelling, the petroglyphs were amazing. Pecking all of these figures into stone must have taken a lot of time: