If California were a country its economy would be the fifth largest in the world (just ahead of the UK). Yet the tech boom is not the starkest way California has ever stood apart from its neighbours. That would surely be the maps depicting it as an island, entire of itself. Below we have featured our pick of these glorious seventeenth- and eighteenth-century aberrations, from a collection of hundreds held at Stanford.

The intriguing story of how the maps came to be deserves a little mapping itself. In the 1530s Spanish explorers led by Hernán Cortés encountered the strip of land we now know as the Baja Peninsula. They mistook it for an island and called it California. Both the name and the notion of it being an island came straight from the pages of a novel — a very popular Spanish romance, Las Sergas de Esplandián [The Adventures of Esplandián] (1510), which described an imaginary realm ruled by Queen Califia:

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. They had beautiful and robust bodies, and were brave and very strong. Their island was the strongest of the World, with its steep cliffs and rocky shores. Their weapons were golden and so were the harnesses of the wild beasts that they were accustomed to taming so that they could be ridden, because there was no other metal in the island than gold.

In 1539, a Spanish expedition led by Francisco de Ulloa discovered that the Baja Peninsula was just that, a peninsula, firmly attached to the mainland. And for the next eighty years published maps reflected this correct view. Then, in 1622, European maps suddenly started showing California adrift, effectively extending the Gulf of California in its northwesterly direction until it meets the Pacific. This island view of California, resembling a floating carrot, was replicated again and again over the next century and a quarter. By 1747, Ferdinand VI of Spain had had enough. He issued a reasonably clear decree, “California is not an Island”. But the royal newsflash travelled slowly. California would appear as an island as late as 1865 on a map made in Japan (see very final image below).

What on earth had happened? How had such a large piece of America been wrenched free? The Spanish clergyman Antonio de la Acensión played a crucial role. Two decades after sailing along the West Coast in 1602–3, Acensión began arguing in letters and books that California was an (enormous) island. It seems he wanted to extend the Gulf of California a great deal further north and so invalidate Sir Francis Drake’s claim of "Nova Albion" for England (as Acensión's version would have had Drake landing on the island of California, rather than the mainland). Acensión's island view was believed by many in Europe. And in the early 1620s maps showing California as an island started appearing in Spain and Holland. The first English one appeared in 1625, next to an influential article about the search for the Northwest Passage. From there the error took flight, deceiving map makers and readers throughout the world for decades.