http://texashistory.unt.edu/ark:/67531/metapth62067/m1/
Good find. I especially like the city insets.
Here's the 1927 edition, which has minimal road content: http://www.davidrumsey.com/luna/servlet/view/search?q=%22National%20Map%20Company%22
Interesting that the 1929 edition still shows "US 46" in Colorado (page xvi), even though that never existed outside of AASHO's initial 1925 planning maps. (The more detailed map shows it correctly as US 40-S.)