and cultural history of the Genesee Valley, and include archaeological artifacts of the Seneca nation, and displays on Mary Jemison, early pioneers, the Genesee Valley Canal and William Pryor Letchworth. The Humphrey Nature Center opened in 2016. Operated year-round by New York State, the sustainable building features classrooms and meeting rooms, a research lab, a butterfly garden, and connections to various trails. Mount Morris Dam Construction of the Mount Morris Dam, at the north end of the park, was begun in 1948 by the United States Army Corps of Engineers under the Flood Control Act of 1944, and completed in 1954. The Genesee River became wider and deeper immediately upstream as a result, but areas downstream were spared yearly flooding which destroyed valuable farmland. The Mount Morris Dam is the largest flood control device of its kind (concrete gravity) east of the Mississippi River. It is in length and rises from the riverbed. The dam proved its worth during the Flood of 1972, saving thousands of acres of farmland and the city of Rochester from flooding. Portage Viaduct The Portage Viaduct (1875) was an iron Erie Railroad bridge located upstream and within view of the park's Upper Falls. The bridge was long and high. Although walking on the structure was considered trespassing, visitors to the park commonly disregarded warning signs in order to view the gorge from the bridge, despite the safety concerns associated with walking on an active railroad bridge. On November 29, 2011, Norfolk Southern Railway announced plans to demolish the Portage Viaduct and build a new bridge approximately to the south of the 1875 structure. Norfolk Southern had offered the old bridge to the State of New York, but the offer was declined due to a lack of available funds to convert the bridge into an observation platform. A steel arch design was approved for the bridge's replacement in late 2014, at an estimated cost of $71 million. The project was completed in late 2017. New train-activated gates at both ends of the new bridge now keep trespassing tourists off it when no approaching freight train is present. Park history The territory of the park was long part of the homeland of the Seneca people, who were largely forced out after the American Revolutionary War, as they had been allies of the defeated British. The Seneca called the land around this canyon Sehgahunda, the "Vale of the