I don't think that was because of UV exposure or anything related. Look at Bedouin tribes even today. They wrap up head to toe, man and woman and child alike, not to avoid tanning but because prolonged exposure to direct infrared will fry you like an egg.

I grew up in the same general region as Wilder, and we sought shade not to avoid sunburn. We were all chestnut brown by the end of summer anyway. It's because the direct sunlight on an August afternoon was brutally hot, and you wanted as little of it to hit your skin as possible.