Favorite Kim Stanley Robinson book?

Kim Stanley Robinson is probably my favorite living author; I don't think anyone does setting and worldbuilding better than he does, yet his stories are largely character-driven.

Here's my favorites of his that I've read:

• Aurora, where a generation ship is on it's way to Tau Ceti
• The Years of Rice and Salt, an alt-history where most of Europe perishes in a great plague in the 14th century
• Shaman, a fictional narrative about the people who painted Chauvet Cave

I love how his stories are about being optimistic in times where that's a hard thing to be. I like the focus on environmentalism and the sublime (Ministry for the Future is basically a solarpunk novel). He mostly writes hard sci-fi, which is my favorite genre, but also spins off into history and philosophy like in Galileo's Dream.

I think most people know his writing from his Red/Green/Blue Mars series, which I love, but he's done so much more than that.

So what's your favorite of his books?