These petal-like flower/pod things were on several trees in my area of west LA for a few weeks, if not months when I took these shots in early September. If you scout around in the last picture in particular, it seems this tree is at least in some places tripinnate, if not merely bipinnate. I'd especially love to know what these are as they seem fairly common in my area. Thanks!
Thanks, Ron! That's the one. There are only about 4 species in Koelreuteria, so not too much to dig through for once :) Thanks again, and happy holidays!