I looked at the UCB specimens and was unable to figure out what the differences are between angustata and pallida. E. expansa is clearly different from these two as you write, but the other two species look very similar to each other. They both vary in color from light to dark. I couldn't see any consistent difference in the elytral rim, shape, hairiness, etc. Perhaps I needed to know what to look for... but I couldn't figure it out on my own! These two species are represented by around 150 specimens each in the Essig collection, from across the state. There were only 9 expansa specimens.

I wish I had an answer, but don't know how to correctly separate angustus from pallidus. I'll try to go over what little I have in terms of descriptions, and will also ask Michael Caterino since they have specimens of all three spp. at SBMNH.
By the way, I stopped at a roadside Ceanothus integerrimus yesterday and found it absolutely buzzing with beetles and other insects. Most of the beetles were Callimoxys sanguinicollis fuscipennis.

also. Will see what the specimens look like.