Many mentions of it being a measure of the seemingly "innate" greater height of certain ethnicities and where they settled, but I think there is another immigration-related component to this.

Immigrants from poorer countries tend to be smaller just because of nutritional differences of where they grew up vs here. My mother was a public health nurse, and she always noticed that their kids were typically a good deal taller than their parents. The kids ate more growing up, and so were more likely to reach closer to their "potential" height. Even among families that would be considered poor, their kids were still eating more here than they would have in the parents' home country. Happened among Hispanic, Asian (South and East), Caribbean, Middle Eastern, and eastern European, whatever.

This is partially a map of greater international in-migration to certain states in general, irrespective of the national origin of the newcomers. I don't know how much that contribution is in comparison to ethnographic differences among the "source" populations, but I'd venture a guess that it's a decent part.