California was the name given to a mythical island populated only by beautiful Amazon warriors, as depicted in Greek myths, using gold tools and weapons in the popular early 16th-century romance novel Las Sergas de Esplandián (The Adventures of Esplandián) by Spanish author Garci Rodríguez de Montalvo. This popular Spanish fantasy was printed in several editions with the earliest surviving edition published about 1510. In exploring Baja California the earliest explorers thought the Baja California peninsula was an island and applied the name California to it. Mapmakers started using the name “California” to label the unexplored territory on the North American west coast.
European explorers flying the flags of Spain and of England explored the Pacific Coast of California beginning in the mid-16th century. Francisco de Ulloa explored the west coast of present-day Mexico including the Gulf of California, proving that Baja California was a peninsula, but in spite of his discoveries the myth persisted in European circles that California was an island.
Rumors of fabulously wealthy cities located somewhere along the California coast, as well as a possible Northwest Passage that would provide a much shorter route to the Indies, provided an incentive to explore further.