The land of California existed as a myth among European explorers before it was discovered. The name “California” derives from a novel written by Garcia Ordonez de Montalvo in the 16th century titled, “Las Sergas del muy esforzado caballero Esplandian, hijo del excelente rey Amandis de Gaula.” It was the fifth book in a series of Spanish romance novels.
“There ruled on that island of California, a queen great of body, very beautiful for her race, at a flourishing age, desirous in her thoughts of achieving great things, valiant in strength, cunning in her brave heart, more than any other who had ruled that kingdom before her. . .Queen Calafia.”
The book described the Island of California as being west of the Indies, “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.“
A few years after its discovery in the 16th century, California already appeared on the map with a reasonably accurate shape. Ortelius’ 1612 atlas was showing California as a peninsula, now separated from the mainland by the mouth of the Colorado River.
However, a century later it was transformed into an island: a shape that was maintained in virtually all the maps of the 17th century.
The book by Antonio de Herrera first shows a sea to the north, joined to the Gulf of California. This might well be the first representation of California as an island (though closer to land than those that followed), and probably became the template for the creation of the myth.
Despite occasional doubt cast upon the legend and contrary evidence, the mistake was reflected on maps for a couple hundred years and became one of the great cartographic errors of all-time.
Upon landing on the Baja California peninsula in 1535, Hernán Cortés believed he had found an island. In describing his discovery as insular he is credited as the originator of the island theory. Cortés thought the body of water later named in his honor, the Sea of Cortés, was actually a strait separating mainland Mexico from the island of California.
In 1539, he sent an expedition led by Francisco de Ulloa to circumnavigate the imagined island and it was Ulloa that named the Gulf of California in Cortés’ honor. Ulloa, however, was unable to lay the myth to rest and correct Cortes’ erroneous belief. The legend lived on.
In 1747, in the face of overwhelming evidence, Ferdinand VI of Spain was obliged to decree that California ‘was not an island’.
https://www.wired.com/2014/04/maps-california-island/ The Phantom Atlas - Edward Brooke-Hitching http://www.designing-america.com/contenido/espanol-el-mito-de-la-isla-de-california/?lang=en