As I recall I see these beetles every year on the same Eriogonum umbellatum, sulfur buckwheat. They sometimes bury themselves in the flower heads. They're probably something obvious, but not to me.

I'm uploading a couple more pictures, not in as good focus but with better views of the head. They may not be the same individual (at one point there were two of these beetles on this plant), but I feel sure they're the same species.

I've saturated all these images to make the yellow look right, and I've used a little unsharp mask.