Self-Defense Is a Perfect Defense to a Charge of Murder
In CA, if the prosecutor fails to prove that you were not acting in self-defense then the jury must acquit you of a murder charge. That's the first step of our wild west concept of self-defense. You have to raise it as a defense. Once you have the prosecutor has to prove beyond a reasonable doubt that no grounds for it exist.
Stand Your Ground
In some states if you have an avenue of safe retreat you must take it. Not here pardner! You have a right to stand your ground in CA even if you could have avoided the danger by turning away.
Pursue Your Attacker?
If you have grounds for self-defense you can not only stand your ground but you can pursue your attacker to assure yourself that no further danger exists. You can hunt him/her down and shoot him assuming you reasonably believed your life was in danger at the time you pull the trigger.
Reasonable Person under the Accused's Circumstances Standard
Bottom line you only have to show that any reasonable person under the same circumstances as you would have feared for his life. The burden the shifts to the prosecutor.
Caution: self-defense is still a narrow doctrine even in the wild west. You can only resort to force reasonably necessary to repel the threat. If you go beyond that you may be looking at 1st degree murder.