Complex sentence: 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.
Split into simpler sentences: Mission San Rafael Arcángel was founded in 1817 as a medical "asistencia" ("sub-mission") of Mission San Francisco de Asís. It was a hospital to treat sick Native Americans, making it Alta California's first sanitarium.