Based on your location, this should be Megetra cancellata, not the present vittata.

comparing with this image of puntata,here I would lean toward vittata.

in thinking that this is M. vittata. Where did you look for vittata? You only gave a link to the one labeled Megetra punctata at Meloidae.com.
I assume you looked at the photos in the MCZ Type Database. That's what was so confusing to me, until I read the Selander revision, and looked at specimens at UC Riverside. I think they've posted the wrong specimen. What's there is actually M. punctata Selander, 1965. I've communicated with John Pinto about this and he agrees. I described the problem to Phil Perkins at MCZ, & hope they'll make the necessary correction. (please see also the updated INFO pages, though that's a work in progress)

This photo isn't crisp enough to unambiguously read the characters. Nevertheless, I think you had the correct name, M. vittata:
dorsal surface of elytra could be finely, and irregularly, reticulated
(not entirely clear from this photo); elytra are abruptly deflexed laterally, showing a well-marked edge (character shared with cancellata, but not with punctata; location: vittata has been collected in that area, but not punctata, the two being allopatric.
I've started moving a few photos, but can't do all at once; will also further update the INFO pages.
Please let me know if you have any suggestions, comments.

I looked at the one you show above, but didn't put much stock in it because it look dried up and discolored to me. I also looked at this one marked probably vittata, then I just figured this specimen didn't look like any of the others.

Yavapai County insects; I had not seen it yet. The Megetra shown there does look like it has the reticulated pitting of
vittata, also the clearly defined edge, and that sp. has been recorded from Yavapai County, AZ.

at least you've got your vote in, and perhaps that's it.
However, I'm not sure that photos will necessarily do without consulting the Selander paper revising this genus, and separating M. punctata.
What are the diagnostic characters? Also interesting is the northern location. I remember coming through Dulce ( > 6800 ft alt.) regularly during the 80's - Jicarilla Apache country.
UC Riverside has specimens of all three spp., & I'll take a look at those later this week.

it would be nice to know the differences between these.

paper tomorrow morning, and will take a look at what specimens are at CSU Northridge. Probably Thursday, I'll look at those at Riverside.
A few posts are clearly cancellata, & we'll see about the rest (though some images may be too small or not sufficiently sharp).