Sorry. I couldn't get the image to show last night for some reason and couldn't delete the post. I tried again this morning and now it seems to be working.
To refine Ilija's answer a bit, I believe that this is an adult molting into winter plumage. The August date confirms that as any juvie in August would be checkerboard fresh.
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The best way to distinguish Sanderling from its relatives is the lack of a hind toe. Although not so obvious here, it is very clear in your post in the main bird forum.