Constructed in 1882, Kinzua Viaduct was the highest railroad bridge in the world, an iron engineering marvel built to access local coal, timber, and oil that stood 301 feet high and spanned 2,053 feet. In 1900, workers rebuilt it to accommodate heavier trains, replacing the wrought iron structure with steel except for the original iron anchor bolts. Active as a railroad bridge until June 1959, it was declared a National Engineering Landmark in 1977, and excursion trains crossed it between 1987 and 2002. After an inspection in 2002 revealed extensive rust and damage from lateral winds, the bridge was closed to trains and pedestrians. On Monday, July 21, 2003, an F1 tornado with winds between 71 and 112 miles per hour struck the side of the viaduct, the iron anchor bolts failed, and 11 of its 20 towers were torn from their bases. In the days that followed, nature began responding as once-shaded areas became nurseries for young plants, fallen trees sheltered insects, mice, chipmunks, and songbirds, and new food sources attracted squirrels, grouse, turkey, deer, and bear. Since 1970, 339-acre Kinzua Bridge State Park has provided access to both this landmark and the natural scenery of the Kinzua Creek Valley.