Alta California (älˈtə kălˌĭfôrˈnyə) [key], term used by the Spanish to refer to their possessions along the entire Pacific coast north of the Mexican state of Baja California. California was often represented on maps as an island some 3,000 mi (4,800 km) long until the 18th-century explorations of the Jesuit father Eusebio Kino proved conclusively that the southern part of the area was a peninsula and the rest of it mainland. Thereafter the peninsula came to be called Baja (Lower) and the mainland Alta (Upper) California.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.