From DFG
Anyone 16 years and older must have a fishing license to take any kind of fish, mollusk, invertebrate or crustacean in California, except for persons angling from a public pier for non-commercial purposes in ocean or bay waters. A public pier is defined in the sport fishing regulations as a publicly owned man-made structure that has the following characteristics: is connected, above the mean high tide, to the main coastline or to the land mass of a named and charted natural island; has unrestricted free access for the general public; and has been built or currently functions for the primary purpose of allowing angling access to ocean waters.
Additionally, publicly owned jetties or breakwaters that are connected to land, as described above, that have free unrestricted access for the general public and whose purpose it is to form the most seaward protective boundary of an ocean harbor are public piers. Jetties, breakwaters, promenades, sea walls, moles, docks, linings, barriers and other structures that are not the most seaward protective boundary of an ocean harbor, are not public piers.