We tend to take them to the northern part of the state in the summer, like Flagstaff. However, it's STILL SUMMER IN ARIZONA, something some people just don't get.
Very true. We see a smaller version of it at Pennsic most years... people who come totally unprepared for a week in either the wickedly hot sun or the pouring rain (the two prevalant Pennsic weather systems).
Historical verisimilitude is all well and good, but try to remember that Europe in the Middle Ages was in a little ice age, and this is NOT Europe, NOT the Middle Ages, and NOT an ice age.
It was also further North, even than where I'm from, nevermind where you're from, which changes the temperature and climate range significantly.
Most Arizonans become early Middle Ages peasants or Viking types: thin, basic cotton and linen dresses, with maybe a linen pinafore-looking thing over it. Baggy drawstring pants and a linen/cotton poet-style shirt for the guys. Undergarments? WHAT undergarments?!
I would have suspected more of a Mediteranian or Middle Eastern flair, but hey whatever works for people. Oh, and on the undergarment.... We're talking about that "easy access" idea again, right?