If you've ever traveled across the country, you'd realize people in Seattle are much different than people in Phoenix who are much different than people in St L

If you've ever traveled across the country, you'd realize people in Seattle are much different than people in Phoenix who are much different than people in St Louis who are much different than people in Boston who are much different than people in Atlanta who are much different than people in Honolulu. You could easily the population of Kansas is as different from the population of California as Colombia is different than the population of Argentina, so I don't think "foreign-born" is a good metric for heterogeneity in the context of this question.