California – History | Britannica

The merchant Sebastián Vizcaíno sailed from Mexico to the southern California coast in 1602, naming San Diego, Santa Catalina Island, Santa Barbara, and Monterey. Working with inaccurate maps, Vizcaíno and several later explorers believed that California was an island and were discouraged when they were unable to chart its surrounding seas.

https://www.britannica.com/place/California-state/History