Following their conquest of the Aztecs in the early 16th century, the Spanish began exploring what is now the western United States, using "Mexico" in 1563 to name the region of New Mexico (Spanish: ""). In 1581, the Chamuscado and Rodríguez Expedition named the region north of the Rio Grande "San Felipe del Nuevo México". The Spaniards had hoped to find wealthy indigenous cultures similar to those of the Mexica's in central Mexico. The indigenous cultures of New Mexico, however, proved to be unrelated to the Mexicas and lacking in riches, but the name persisted.