In July 1539, Cortés sent Francisco de Ulloa to sail the Gulf of California with three small vessels. He made it to the mouth of the Colorado River, then sailed around the peninsula as far as Cedros Island. This proved that Baja California is a peninsula. The next year, an expedition under Hernando de Alarcón ascended the lower Colorado River to confirm Ulloa's finding. Alarcón may thus have become the first to reach Alta California. European maps published subsequently during the 16th century, including those by Gerardus Mercator and Abraham Ortelius, correctly depict Baja California as a peninsula, although some as late as the 18th century do not.
In July 1539 Cortés sent Francisco de Ulloa to sail the Gulf of California with three small vessels He made it to the mouth of the Colorado River then sailed around the peninsula as far as Cedros Island This proved that Baja California is a peninsula The next year an expedition under Hernando de Alarcón ascended the lower Colorado River to confirm Ulloa's finding Alarcón may thus have become the first to reach Alta California European maps published subsequently during the 16th century including those by Gerardus Mercator and Abraham Ortelius correctly depict Baja California as a peninsula although some as late as the 18th century do not