Oklahoma is where Route 66 goes from the Midwest phase to the "Grapes of Wrath" phase. Entering from Kansas, the sight of a horse statue (and a fair number of horses in the fields) and the Oklahoma welcome sign saying "Native America", you know there's a shift.
Trivia: More than 25 Native American languages are spoken in Oklahoma, the most of any state.
The first settlement you enter inside Oklahoma is little Quapaw (pop. 984). Though small, it has two mentions in famous shows: the TV show M*A*S*H, when character B.J. Hunnicutt mentioned that his father-in-law (named Floyd) was a resident of the town, and as one of the towns Jud had worked in previous in the famous movie Oklahoma. Quapaw thrived on mining for a while, but has since settled into being a quiet, yet pleasant stop along Route 66.