Solstice Marker

Ok, since this Blog is about Petroglyphs, I wanted to show this off. In north Phoenix there's a group of small mountains known as the Hedgepeth Hills. On the north east face of one of the mountains there are about 1500 petroglyphs and the site is maintained by ASU. This cool little place is called the Deer Valley Rock Art Center. Anyway, the southernmost little hill seemed like a good place to look for petroglyphs.
Up the mountain I went, looking for whatever there I might find. I found a couple US Geoditic Survey markers, and a grouping of large rocks in the formation of a large rectangle. Seems like that wouldn't form naturally, so I'm half inclined to go back up with a shovel and do a little digging! Probably millions of dollars worth of Aztec gold, the Spear of Destiny, or maybe even the Ark of the Covenant!
Seriously, I'll leave the gold, spear, and Ark right where they are lest they fall into the wrong hands.
But I did find something cool. A petroglyph unlike anything I'd seen in the area. The style was not consistent with the Hohokam glyphs one typically finds around here. I doubted that it was authentic, but took some pics anyway. Later I contacted the city archaeologist, sent him a copy of the pics I took, and got a reply from his assistant. According to him, it looks like a late Hohokam or early Pima solstice marker! It's widely accepted that the Hohokam were good stellar observers, and were able to determine the longest and shortest day of the year.
This information came to me just days before the summer solstice, so I had some time to prepare. I went back up the mountain at sunrise and sunset. Unfortunately I didn't see any interaction between shadows and the glpyh. Maybe it's a winter solstice marker!