A number of historical USGS topo maps of Arizona are now online at the University of Texas Library for viewing or downloading. [right, Phoenix, 1:24,000, 1914] These are part of the Perry-Castañeda Library Map Collection.
The Arizona set includes pre-1945 maps, at scales of 1:62,500, 1:125,000, 1:250,000 and special sheets (1:12,000, 1:24,000, and 1:48,000).
Thanks to our student intern Leah for spotting this resource.