I think that the origin of Azusa comes from “A-to-Z-USA..... meaning California is made up from all comers across the world from A to Z
Azusa--The Andrews Sisters (1946)
"Azusa stands for everything from A to Z in the U.S.A." has been a phrase used to promote the city by organisations such as the Chamber of Commerce for many years. The place name "Azusa" dates to the Mexican Alta California era in the 19th century when Azusa was used to refer to the San Gabriel Valley and the San Gabriel River. It appears to have been derived from the Tongva place name Asuksagna. The area was part of the Tongva peoples' (Gabrieleño Indians) homeland since at least 55 BC.”
My great-grandmother on my fathers side was a Gabrieleno Indian. According to family lore, she was quite the notorious figure.