The Oklahoma Department of Transportation has scanned and put online its archive of state highway maps, dating from 1873 to the present day.
These Acrobat files also contain detailed layouts of bigger cities and scenes from the road. Roadologists will find a lot of useful material here.
For instance, the 1926 map‘s roads are mostly unmarked. But the 1927 map, which was printed shortly after the numbered system for U.S. highways was established, shows Route 66, which also was known as Highway 7 from the Kansas line to Oklahoma City.
(Hat tip to Batesline.com.)