>>86321402I think Utah is the problem here
A culture run by mormons isn't going to have much genetic variation, they don't trust or associate with non-mormons and they think people with dark skin are descendants of the "lost tribe of israel" i.e. they have no souls. So it's mostly just the same genes getting passed around from family to family.
Also they marry early so by age 14 most of the potentially hot girls are getting scooped up by polygamists. Why stay skinny when you are the sad 5th wife for a 45 year old pervert?