The San Joaquin River region remained largely unknown except for the fact of its existence until 1806, when Spanish explorer Gabriel Moraga led the first of several subsequent expeditions into the Central Valley, in order to find potential mission sites. Moraga started out from Mission San Juan Bautista, in present-day San Benito County, on September 21 of that year and traveled east into the San Joaquin Valley. The group skirted the western foothills of the Sierra and christened many place names that remain in use today. In 1807 and 1808, Moraga set out again to the San Joaquin Valley. It was during one of these expeditions that he gave the river its present name, after St. Joachim. He also gave names to many tributaries of the river, such as the Merced River ("El Río de Nuestra Señora de Merced", "River of our Lady of Mercy").