The Iowa Governor’s Mansion is the setting tomorrow for a celebration of reading, spring and family. Iowa First Lady Christie Vilsack says the 2nd annual “Spring Fling” at Terrace Hill is zeroing in on books, learning and fun.Mrs. Vilsack admits it may be a little difficult to recognize her and the other grown-ups who are hosting the event at the Des Moines mansion — since they’ll all be in costume as characters from the “Wizard of Oz.”Mrs. Vilsack will be Glenda the Good Witch while the Governor will be made up as the Scarecrow. Lieutenant Governor Sally Pederson will dress as Dorothy. Mrs. Vilsack says the promotion of literacy is the prime goal of Spring Fling.Spring Fling will also feature tethered hot air balloon rides, simulated tornadoes from the Iowa Science Center, gigantic inflatable rides, face painting, a petting zoo and pony rides. It runs Sunday from noon to 3 p-m.