Fleurieu Peninsula
The Backstairs Passage is a strait in South Australia lying between Fleurieu Peninsula on the Australian mainland and Dudley Peninsula on the eastern end of Kangaroo Island. The western edge of the passage is a line from Cape Jervis on Fleurieu Peninsula to Kangaroo Head (west of Penneshaw) on Kangaroo Island. The Pages, a group of islets, lie in the eastern entrance to the strait. About 14 km wide at its narrowest, it was formed by the rising sea around 13,000 years ago, at the end of the Pleistocene era, when it submerged the land connecting what is now Kangaroo Island with the Fleurieu Peninsula. Backstairs Passage was named by Matthew Flinders whilst he and his crew on HMS "Investigator" were exploring and mapping the coastline of South Australia in 1802.