 In the early 19th century , several military expeditions sent by Spanish colonists from coastal California traveled into the Central Valley . One of these trips , headed by lieutenant Gabriel Moraga , arrived on the south bank of the Merced River on September 29 , 1806 . They named the river Rio de Nuestra Señora de la Merced ( River of Our Lady of Mercy ) , who is the patron saint of Barcelona and is celebrated on September 24 . Another expedition to the Central Valley in 1805 also named the Kings River upon reaching it on January 6 , 1805 , which is the feast of the Magi or Epiphany . Moraga 's expedition was part of a series of exploratory ventures , funded by the Spanish government , to find suitable sites for missions in the Central Valley and the Sierra Nevada foothills . In 1808 and 1810 , Moraga led further expeditions along the lower Merced River below Merced Canyon , each time coming to nothing . Eventually , plans to establish a mission chain in the Valley were abandoned . In 1855 , Merced County was created , named after the Merced River . 
