Between 1915 and 1922, the National Old Trails Highway was surfaced with gravel between Topock and Oatman as well as between Seligman and Holbrook. A small section just outside Ash Fork was also reconstructed and realigned at this time, becoming the first road to ever be paved using volcanic cinders. The highway was also paved through Flagstaff in 1921 using concrete. In 1921, the Arizona state highway system was reorganized again following the passage of the Federal Aid Highway Act of 1921. The state no longer referred to the National Old Trails Road as the Santa Fe Highway, and instead re-designated Topock–Kingman–Ash Fork Highway and the Ash Fork–Flagstaff–Winslow–Holbrook Highway west of Holbrook. East of Holbrook, the original route through Springerville became the Holbrook–Springerville–New Mexico State Line Highway, while the recently constructed new route through Lupton became the Holbrook–Lupton Highway.