The idea that California
was an island arose in 1602 in reports by Fr. Antonio de la Ascension,
and was picked up by map makers in London and Amsterdam. The myth was
dispelled in 1701 by Fr. Eusebio Kino, but erroneous maps continued
to be issued until late in the 18th century.
On the high value of a set of stamps issued by Mexico
to commemorate the 400th anniversary of the first ship to make a round
trip from Mexico to the Philippines, the map shows California as an
island. Although the voyage commemorated by the stamp occurred before
the island-California myth arose, the error could be described as an
error of source.