Today I had the chance to visit the Casa Grande Ruin located between Phoenix and Tucson (we never got here during our 8 months living in Tucson). Casa Grande is a prehistoric ruin of an ancient astronomical observatory (and no, it isn't the observatory that I worked at while living in Tucson in the 1990s).
The shelter is obviously there to protect the ruins from further erosion. It's a huge building 3-4 stories high, and specifically aligned for the solstices etc.
Unfortunately, civilization is encroaching on the site and it is almost surrounded by houses etc of the town of Casa Grande. Just outside the gate is a strip mall (these things seem to be breeding faster than rabbits in Arizona). just behind this restaurant is a Wal-Mart.
