Wallpack Ridge is a long, narrow mountain ridge in northwestern New Jersey that stretches about 25 miles through the Ridge and Valley Appalachians, dividing the Wallpack Valley from the Delaware River, or Minisink, Valley and containing the watershed of Flat Brook and its main tributaries. Rising to 928 feet, it is significant both as a defining landscape feature and for its connection to a major abandoned dam project. In the 1950s and 1960s, federal land seizures for a proposed Delaware River hydroelectric reservoir would have flooded the nearby Walpack Valley, but the plan was canceled, and the land later became part of the Delaware Water Gap National Recreation Area.