Quote from Wikipedia:

Mission San Rafael Arcángel was founded in 1817 as a medical asistencia (“sub-mission”) of the Mission San Francisco de Asís as a hospital to treat sick Native Americans of the Bay Area, making it Alta California’s first sanitarium.The weather was much better in the North Bay than in San Francisco, and helped the ill to get better. It was never intended to be a stand-alone mission, but nevertheless grew and was granted full mission status on October 19, 1822.