be interesting to know what you base your identification on?? If you read the description in Powell & Oplers "Moths of Western North America" P. modesta fits much better than P. occidentalis. I've photographed the latter from a nearby locality and they're quite different even to an untrained eye.

Sorry about not elaborating earlier, I meant to, but I was a bit distracted.

I made the determination as P. occidentalis based on the following factors:

Firstly, the locality. P. occidentalis replaces P. modesta in southern AZ, though the two species are sympatric in New Mexico and potentially (likely) in Northeastern Arizona. Secondly, the overall coloration of this individual is more brown yellow, as oppose to the grayish coloration of P. modesta. Additionally the blue marking at the anal angle of the hindwing is rather faint, being more pronounced blue in P. modesta. Also note that the black bit of the blue area bisects the blue rather than "capping" it as seen in P. modesta (Tuttle used this trait as the primary distinguishing feature between the two species). Finally, the PM line is very prominent and wavy, a characteristic not usually seen in P. modesta (at least in those from much further east, in the sympatric regions "P. modesta" may have prominent PM lines.

Though I do not have Powell & Opler in front of me, I do have Tuttle's Hawk Moths of North America and Hodges' MONA fascicle. Your specimen is a clear match to P. occidentalis depicted in both volumes. Powell & Opler seem to be a little misleading by saying that P. occidentalis has a "disk shaped" spot in the anal angle, and P. modesta a triangular one, because the black spot is arched even in P. occidentalis, giving it a nearly triangular shape.