Ulloa, Francisco de (fränħēsˈkō ħā ōlyōˈä) [key], d. c.1540, Spanish explorer in Mexico. Against the orders of Viceroy Antonio de Mendoza, Hernán Cortés sent Ulloa to explore the Gulf of California. In 1538–39 he sailed to the head of the gulf, thus proving that lower California was a peninsula.
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