From 1650 until about 1776, many Europeans believed that California was an island. One Response Charles May 16, 2014 To be clear, the “California” in these maps is not equivalent to the US state of California, but the California peninsula in Mexico. No one thought that the chunk of the continent that is now California state was an island. Reply Leave a Reply Cancel Reply Your email address will not be published. Name* Email* Website Comment Notify me of follow-up comments by email. Notify me of new posts by email.