A bit late with this email, but I wanted to add a bit of clarity about what the golden-plover was and my stance on the bird.
First, I wanted to clear up that in the field I thought the bird might have been American but I was really making a statement of uncertainty; Lesser Golden-Plover-- no more, no less. The bird was decently far and fairly ambiguous. Closer photos by Michael Park and Alex Henry explain some of the field marks I saw on the bird that made me think it might have been American, including missing tertials, which made the primary projection appear quite a bit longer in the field than it might have appeared otherwise. Also quite an interesting exploration into how well cameras work, and how much this ID of American v Pacific Golden-Plover might be oversimplified. For as much as cameras are good for, different cameras can really paint the same bird in different ways: Early sets of photos of this bird looked quite a bit different from each other, and from the bird in real life. Thanks again to Michael Park for pulling out the huge lens. It was helpful.
Concerning what the bird is, at this point calling this bird a Pacific Golden-Plover seems fine. It is obviously a pale bird, but having emailed several well versed in this ID, we've all agreed the following features point to Pacific (based off M. Park's photos, there was less agreement as to the bird's identity using Alex Henry's photos):
--A less than obvious (muted) supercillium and other facial markings
--That p10 (the primary furthest from the tertials) extends beyond p9, but only barely so
--That the tail tip to primary tip length, relative to bill length, is decently short as far as Lesser gp go, but rather long for a Pacific (but still within expected Pacific range)
--A rather heavy, more pot-bellied body shape
A myriad of other features were discussed that pointed towards Pacific, but those four seemed to come up the most, and I think would be the most useful in the future.
A couple different people I emailed independently (and very cautiously) suggested that hybrids would be worth looking into, but it was also noted that hybrids between these two species are rare enough it should not be a reason to keep this bird as a slash. I would agree, especially considering our location on a regular migratory path of Pacific Goldens.
Interesting was the note that Pacific Golden-Plovers that breed in Asia can have primaries quite a bit longer than the Pacifics that breed in N. America (approaching American Golden in length, or perhaps equal to the shortest projections on Americans?), so perhaps birds seen poorly with moderately long primary projections should be left unidentified in the field (does not apply to this bird). Also interesting (but wouldn't apply to this bird either) was the comment that some American Golden-Plovers have been known to only show 3 primary tips.
Anyway, hopefully this helps. Congratulations to the Wills on the find.