Seh-ga-hun-da was the land called the Vale of the Three Falls. The Upper Falls, seventy feet high, has a deep horseshoe shape, and the top of the falls is part of the strata named the Nunda Sandstone. Similar stone, known locally as Portage Bluestone, was quarried south of Portageville. In low water, some concrete can be seen at the crest of the falls that was placed there in 1878 to slow erosion. The Middle Falls, the largest of the three, is one hundred seven feet high and two hundred eighty-five feet wide, and it has changed very little since Letchworth's time because of its many hard, resistant sandstones. The Senecas believed that the great beauty of Ska-ga-dee, the Middle Falls, inspired the sun to stop at midday in admiration. Around the bend downstream and out of view, the Lower Falls is constantly changing because the softer shales that dominate in the lower canyon erode easily. Its harder caprock, known as Table Rock, forms dozens of waterfalls on tributaries throughout the park.