LORETITO, Mexico — It's the end of the day here. Down one lonely street two young boys kick a ball between them, as an elderly woman slowly makes her way nearby. On most days, this little town about 300 miles northwest of Mexico City feels like the set of a Hollywood movie — its narrow streets and alleyways silent, stark, deserted. From the sidewalk outside his small liquor shop, Edmundo Cruz takes in the vast emptiness, pointing out one house after another left vacant when families headed north — to Seattle. It is said more Loretito people now live in...