more likely the elm leafbeetle; even though the antenna suggest Trirhabda

I know next to nothing about beetles but couldn't help looking around for more info on how to separate these two genera. My bug has its third antennal segment distinctly shorter than segment 4. Is this conclusive for Trirhabda? Looking at other BugGuide photos of the two genera, it seems to be. The antennal segments of Xanthogaleruca don't seem to match my beetle. Thanks for any additional info! I've added another image I found, in case it helps at all. Sorry I don't know what the plant is.

Dear Nick, looking at the pictures in the guide, I confirm your observation. X.luteola, unlike Trirhabda spp., has the 4th antennal segment a little shorter than the 3rd. This seems to be diagnostic on the species level only, because a second species of Xanthogaleruca found on an European page approaches Trirhabda in this respect.
The plant on your pictures may be an Asteraceae (a family preferred by Trirhabda spp.), but also may well be something else. At least it looks pretty xeromorphic, indicating that elms are unlikely to be around.

I grew up there. It's high desert like much of Colorado but elms were plentiful were moisture was availble.

the segments character seems to be variable and not fully conclusive. It generally applies but not allways shown by this specimen. Trirhabda have a broader black sutural stripe and don´t have a smooth pronotum like this beetle. The markings on head, pronotum and elytra fit X. luteola too.

Thanks so much for the information, Rob! I really appreciate the help. I definitely see what you mean about the sutural stripe.