The penultimate (if you go West) and one of the toughest sections of Route 66 passes through Arizona. Several original sections of the route still exist. The state and a couple of towns in Arizona get name-checked in the Route 66 song, including Winona. Winona is not even an incorporated community and was simply chosen because it rhymed more or less with Arizona. That isn't to say it isn't worth a quick detour off the Interstate, as an original bridge from Route 66 still stands - but that is about all there is to see.
I didn't get to spend much time in Arizona, just a stopover in Holbrook (a fascinating town), but some sections blew me away. The old Route 66 section known as the Oatman Road is spectacular. It winds over mountains, goes through flood plains and has some cute little communities along the way, including Oatman with its donkeys. Back in the day, this was the toughest section of Route 66 - reputedly cars reversed up the steeper sections because they got more traction in reverse than in first (and I guess they sort of had front-wheel drive!).
Arizona was hot and sunny when I crossed the state line, but slowly - as the altitude climbed - the temperature dropped. I thanked my good fortune that, in a car with so-called all-weather tyres, I had made it so far without a problem. As I left Arizona, I left behind snow and ice and sub-zero temperatures. Inadvertently I made all of my road trips at pretty much the optimal time - OK, I could have hit the North East a little later to catch the leaves, but I went to national parks in the days before they closed for the year, and got over mountain passes that would have been closed a few weeks later.
Name check for a great street name in Holbrook: Bucket of Blood Street.