The other pic of this beetle looks identical to the Blethisa quadricollis from the Smithsonian that's in the Guide.

B. quadricollis, B. oregonensis, B. multipunctata aurata according to the 1993 catalogue by Bousquet & Larochelle. According to Lindroth (1961-1969), B. quadricollis is the largest at > 15 mm while others are < 13.5 mm. Also B. quadricollis has pronotum with relatively rounded hind angles, but images suggest sharper hind angles that would be consistent with the other two species. Measuring body size would have been most helpful for ruling in or out B. quadricollis. This certainly could be B. quadricollis based on limited detail of images, but I feel safer with just "Blethisa" until I'm convinced otherwise. See the difficult image separations here.

I'll check through the other images I have to see if they show the back margin of the pronotum better, but I *think* I picked the best images I got of this specimen. I may also so if I can do a little reconstructive measuring...but that will only help us if this was a full grown B. quadricollis and is 15 mm or larger, of course. Anything 13.5 mm or less still means it could be any of the three.

They stay almost same size after they emerge from pupae. Adult beetles do not shed exoskeletons to grow larger nor do they simply "grow" without shedding.