Calver Island, a midchannel island in the Susquehanna River in Swatara Township, Pennsylvania, became inhabitable about 5,200 years before present as two shoals gradually merged into one landform. The site preserves evidence of Native American use from the Early Archaic through the Late Woodland periods and is especially significant for its unusually intact stratified layers from different eras, among the best-preserved stratigraphic records in Pennsylvania. Archaeological interest was identified in the 1970s, and major investigations in the 2000s during bridge replacement planning confirmed the island’s importance. In 2007, it was found eligible for listing on the National Register of Historic Places.