The highest point on the island, almost exactly at its center, is Mount Caroline Livermore at a height of 788 feet (240 m). The island is almost entirely in Marin County, California, although, there is a small sliver (0.7%) at the eastern end of it (Fort McDowell) which extends into the territory of San Francisco County. The island is separated from the mainland of Marin County by Raccoon Strait
