You don't want to be building anything underground in Tempe. There's a nasty layer of natural concrete called Caliche about a meter below the surface in much of

You don't want to be building anything underground in Tempe. There's a nasty layer of natural concrete called Caliche about a meter below the surface in much of the area. Archaeologists hate the stuff because it's so expensive and time consuming to dig through. The local indigenous people have been building sustainable apartment blocks called pueblos for a long time though. They're surprisingly nice during the summer (approx. 80F inside), even without AC.