Saint Monica is the patron saint of mothers with wayward sons. There's a Santa Monica Boulevard on the Westside of town, but wayward sons also live across the Orange County line in Fullerton. Santa Monica Avenue borrowed the name from the city on the bay.
Ginny King, who wrote "The Street Where You Live: Why Did They Name It?", says the "Santa Monica" name may have come from a soldier who was part of Spanish explorer Gaspar de Portola's expedition up the California coast in 1769.
"Legend says that a soldier noticed a small waterfall dropping into a shadow and compared it to tears shed by Saint Monica over her wayward son Augustine. But he turned out all right, too. Saint Augustine."
Father Juan Crespi, who also was on that Portola expedition, had a different name for the area. He called it "San Gregorio" or Saint Gregory, but that name didn't stick. "Santa Monica" did.