Very cool! Thanks for the link. I hope they keep adding topos to the Arizona page. I absolutely love looking at old maps and photos. In my job, I'm often looking for older maps such as these. I already have the San Francisco Mtn. quad but the others are new to me. It is possible to georeference these old maps using newer topos. The process isn't perfect but it'll get you in the ballpark. This makes it possible to quickly get coordinates from the old topos to use in your GPS. Very handy for locating sites.
I've got an assortment of northern Arizona topos from the late 1800s to the 1940s in digital format that I'd be more than happy to share.