Barrenjoey is a locality in the suburb of Palm Beach, at the most nothern tip of Pittwater. The headland is mostly made up of hawwkesbury sandstone which overlays Narrabeen shale. Around 10,000years ago the headland was cut off from the mainland due to the rising sea level; subequent buildup of a sand spit or tombolo reconnected the island to the mainland (a 'tied island'). it is the location of the Barrenjoey Head Lighthouse, a lighthouse that was first lit in 1881.