This is a clear case of false advertising. There are no mules going up Piestewa  (a.k.a. Squaw) Peak. Instead, you have a line of hikers which can be quite an impressive sight during the cool winter months on a weekend day. There are at least 34 people visible on this photo. There is really no danger of getting off the trail at Piestewa Peak. First, the path is well maintained and so obvious that it is easily traversed even at night under moonlight. Second, there are a lot of hikers to show you well in advance where the trail lies.