I did debate on where to place this specimen; but only considered appearance of wing patterns based on images at MPG. My second choice was P. californiaria.

I spent some time today reviewing images of P. personaria, P. californiaria, and P. ursaria here on BugGuide, MPG, and at BOLD. My intuition is more than a few of these specimens ID is in error.

I also read the info and viewed images of these 3 species within "A Revision of the Moth Genus Plataea (Lepidoptera, Geometridae) by F. Rindge;" and this discussuion here (1) on BugGuide, which concluded with your own comment.

Rindge does states the range of P. ursaria as being montane, rather than the coastal plain, from where my specimen was found. P. ursaria, is, as you noted larger. So I think it would be safe to say, based on Rindge, my specimen is not P. ursaria, and is P. personaria.

I ran some DNA sequences at BOLD and was surprised to see how genetically similar P. ursaria and
P. californiaria specimens were; and yet were distinct from P. personaria.

I would think that these three species would benefit from a good review based on many new specimens being examined: via genitalic disection, DNA sequencing, good photos showing variation of wing patterns; and accurate range data.

Thank you for your insight, and concerns for accuracy in moth identification!