Tipuana tipu?

Albizia julibrissin silk tree. Maybe.

http://www.desert-tropicals.com/Plants/Fabaceae/Albizia_julibrissin.html

Yeah, Looks like a Mimosa. The smooth trunk convinces me.

I don't think it's mimosa. They are hardy to about 5 degrees, so that doesn't fit the description given of "not hardy in cold." (mimosa grows as far north as southern missouri.)

Tipu is another good guess, but I doubt it would suffer winter injury here in the valley. (i've seen it in inland southern california in upper 20's temps )

I don't know the answer, but let's keep up the search gang...

mimosa can live through hard freezes with no damage. they also have pretty extensive root systems and won't usually blow over, even in a strong wind (I have two of them, they grow wild in the south, where i'm from). they bloom in the spring and throughout the summer and are very fragrant. they aren't evergreen, mine will be naked in a couple weeks. however, the bark in the above pic does look like mimosa.
debbie

Could it be a feather bush/tree?

It's not mimosa, Albizia or Feather bush (Lysiloma). They have bipinnately compound leaves, in other words the leaflets are divided once more than the leaf in the photo.

Any other ideas?

I give up. I had 2 Mimosa trees and both died from a fungus at the roots. I really liked the chocolate one & was bummed big time when it died.

u_u, could you post another photo showing more of the tree/bush? Are there thorns anywhere? It looks very much like wild sprouts (of palo verde?) that pop up in my yard, but they have thorns.