The southernmost point of NorCal is actually somewhere around Big Sur, although if you head further inland then parts of SoCal extend much further north, with residual influence felt as far up as Sacramento.
San Diego and the O.C. are further south than L.A. proper, but there is nothing in the world more SoCal than L.A., nor should anyone desire such a trait. L.A. is like a black hole of SoCalness, with the caveat that the black hole would also have to have many of the quantum properties of some kind of galactic unwiped anus, the force of whose anosity was so great that it sucked itself into an infinite anal well of SoCalhood.
I believe the mathematics to describe this process were first theorized by Stephen Hawking in the 1970s, but thinking too closely about the magnitude of Los Angeles' disgusting SoCality caused him to fail his Horror check and be instantly overcome with Lou Gherig's disease leading to almost total paralyzation.