There are three "hotspots" on this image which will give you close-up views of the petroglyphs inside the niche and just to its left.  Click them.

These images give us a visual clue as to when they were made:  men are riding on horses as they hunt a deer or an elk.  Horses were unknown to the Native Americans until the arrival of the Spaniards in the late-1500s.  These images could not have been made before that time.