The Island of California refers to a long-held Spanish misconception, dating from the 16th century, that California was not part of mainland North America but rather a large island separated from the continent by a strait now known as the Gulf of California.
One of the most famous cartographic errors in history, it was propagated on many maps during the 17th and 18th centuries, despite contradictory evidence from various explorers. The legend was initially infused with the idea that California was a terrestrial paradise, like the Garden of Eden or Atlantis.
The first known mention of the legend of the "Island of California" was in the 1510 romance novel Las sergas de Esplandián by Garci Rodríguez de Montalvo—the sequel to Montalvo's more famous tales of Amadis de Gaula, father of Esplandian. He described the island in this passage:
Know, that on the right hand of the Indies there is an island called California very close to the side of the Terrestrial Paradise; and it is peopled by black women, without any man among them, for they live in the manner of Amazons.
It is probable that this description prompted early explorers to misidentify the Baja California Peninsula as the island in these legends.
In 1533, Fortún Ximénez, a mutineer on an exploring expedition sent by Hernán Cortés, discovered the southern portion of Baja California, around present-day La Paz. He was killed by natives but his men returned to New Spain and gave report of their find. In 1535 Cortés arrived in the bay there and named the area Santa Cruz; he attempted to start a colony but abandoned his efforts after several years due to logistical problems. Cortés' limited information on southern Baja California apparently led to the naming of the region after the legendary California and to an initial but short-lived assumption that it was a large island.