A historic steam train is puffing across Iowa this weekend, and will crisscross the state all month. Mark Davis at the Union Pacific Railroad says the “Challenger” steam locomotive normally has a home and maintenance crew in Cheyenne, Wyoming.It was built in 1943 and is older than any of the guys who work on it. Specially trained crews maintain the world’s largest operating steam locomotive, and Davis says this weekend’s trip from Council Bluffs to Boone is the start of a three-week odyssey.He says it’ll be in nine states, over 3,100 miles. Davis calls the steam train a piece of moving history.He says people know they’re coming and will come out with their lunch to watch it pass. Davis has gone along on previous missions, and watched the crowds. He says there’s a lot of emotion.Senior citizens remember riding or working on trains, and kids think they’ve seen a dinosaur in a zoo. On Tuesday the train starts up again to go to Clinton, then on to several other states before it returns June 18. In all, the Challenger will steam through half a dozen states before returning to its base in Wyoming.