Hernando de Alarcón, a Spanish navigator of the 16th century, born in Trujillo, Extremadura, noted for having led an early expedition to the Baja California Peninsula, meant to be coordinated with Francisco Vasquéz de Coronado's overland expedition, and for penetrating the Colorado River into California.
Little is known about Alarcón's life outside of his expedition in New Spain.
He set sail on May 9, 1540, with orders from the Spanish Viceroy Antonio de Mendoza to await at a certain point on the coast the arrival of an expedition by land under the command of Coronado. The meeting with Coronado was not effected, though Alarcón reached the appointed place and left letters, which were soon afterwards found by Melchior Diaz, another explorer.
Alarcón sailed to the head of the Gulf of California and completed the explorations begun by the Spanish explorer Francisco de Ulloa the preceding year. During this voyage Alarcón proved to his satisfaction that no open-water passage existed between the Gulf of California and the South Sea. Subsequently, on 26 September, he entered the Colorado River, which he named the Buena Guia. He was the first European to ascend the river for a distance considerable enough to make important observations. On a second voyage, he probably proceeded past the present site of Yuma, Arizona. A map drawn by one of Alarcón's pilots is the earliest accurately detailed representation of the Gulf of California and the lower course of the Colorado River.
Alarcón is almost unique among the conquistadores in that he treated the Indians he met humanely, as opposed to behavior that was otherwise inhumane. Bernard de Voto, in his 1953 Westward the Course of Empire, observed: "The Indians had an experience they were never to repeat: they were sorry to see these white men leave."