The Tree of Life sculpture at the corner of Galvin Parkway and McDowell was built in 1991 as a boundary art project using transportation 1% for the arts program (1% of all highway programs funding went to support the arts). Scottsdale & Phoenix arts programs were also involved. Anyhow, the sculpture is supposed to be a terraced 'garden' collecting and distributing rainwater to several terraces all in the shape of a tree. Kind of neat.
It is also supposed to be a solstice marker. I can find very little in that regard on-line, and I think I now know why that is. The winter solstice was Dec 21, but as solstice means "sun stands still" it should still have been the same on the 22nd and 23rd. The 21st had clouds and the 22nd did as well. The 23rd was a clear day, and I climbed atop the shortest of the pillars supposedly aligned with the winter solstice sunset.