Corinthian Island is a former island in the San Francisco Bay, that was later attached to the mainland. It is in Marin County, California, by the Tiburon Peninsula. Its coordinates are 37°52′22″N 122°27′32″W, and the United States Geological Survey gave its elevation as 72 ft (22 m) in 1981. It appears on a 1950 USGS map of the area.