Frontier City is a former Six Flags park in Oklahoma City. It was actually one of the original SF parks, and the headquarters for the entire chain were located there until last year. The park was sold last year to PARC, who have done a fairly good job with it thus far, and apparently have big plans for the place. That's good too, because the park hasn't seen a new coaster since 1991, and the last major ride that isn't an up-charge came in 2001.
It's an OK place, but it really needs something new to make it worth the entrance fee.