"Boone Viaduct over the Des Moines River, four miles west of Boone, Iowa, on main line of Chicago & Northwestern Railway. Length 2,685 feet. Height 185. 5,600 tons of Steel. Length of center span 300 feet. Largest Double Track Bridge in the World." --t.p. The Pratt deck truss bridge was built in 1899-1901, designed by the Chicago and Northwestern Railroad and constructed by the American Bridge Co. (Ambridge, PA). It is located in the Boone-Ogden Cutoff and crosses the Des Moines River at a point where the bluffs on either side are about 3000 feet apart. The bridge was nicknamed for the Iowa railroad heroine, Kate Shelley, also spelled Shelly. In 1881, when she was 17 years old, Kate Shelley risked her life to warn a passenger train by crossing the Des Moines River Bridge near Moingona at night, during a thunderstorm. Her goal was to warn the passenger train that the next bridge was out. That train had already been stopped. She then led rescuers to two men still in the swollen, flooded Honey Creek near her house, and they were saved. Her bravery was heralded in many newspapersListed in the National Register of Historic Places.