Alarcón, Hernando de (1500?-?), a Spanish explorer. He and Coronado were sent out in 1540 to discover the fabled Seven Cities of Cibola. Alarcón commanded a naval expedition while Coronado conducted an overland search. Alarcón discovered the mouth of the Colorado River and proceeded by boat up the river to search for the Seven Cities and to make contact with Coronado, but he failed to find either. On the return voyage he explored the Gulf of California.