The official date for the founding of the city of Los Angeles is September 4, 1781. The name given by the founders was “El Pueblo de Nuestra Señora de los Angeles de Porciuncula”, or “the town of Our Lady of the Angels of Porciuncula.”
The Porciuncula (“little portion”) is the small church in the fields below the Italian town of Assisi. St. Francis was given this abandoned chapel by Benedictine monks who had been respoonsible for it. Francis and his first group of followers lived in this small church. It was in the Porciuncula that St. Clare of Assisi (founder of the “Poor Clares”) made her vows as a nun to pray for Francis and his missionary work. Francis himself died in the field nearby in AD 1226 and another small chapel was built to mark that spot. The crowds coming to venerate St. Francis overwhelmed the tiny churches and in 1569 the larger church of Our Lady of the Angels was built around the tiny churches to protect them and provide a place for pilgrims to gather.
It is said that whoever prays at the Porciuncula on its feast day (August 2) will have all their sins forgiven. There are several replicas of the Porciuncula in the United States for people who cannot travel to Italy itself to pray at the original site.
The Spanish missionaries who travelled up the coast of California establishing a series of missions dedicated to several different saints (such as St. Monica, St. Barbara, St. Diego, St. Bernadino) were Franciscan friars. The names they chose for the missions were all saints important to the Franciscans for various reasons. Two missions were named for places directly related to the history of the Franciscans themselves.
St. Francis is thus the patron not only of San Francisco itself but of Los Angeles as well.