I can tell you for a fact that the knife IS legal according to California state law - penal code 17235. It's legal because it doesn't open by the force of a spring released by pressing a button and because it has a ball detent. The word "detent" is specifically mentioned in that statute.
Of course, different cities and counties in California have their own laws. Some have restrictions on blade lengths.
I wouldn't waste my time calling the District Attorney, I don't imagine you would ever get through to them. And even if you did, they might just tell you that the knife is illegal, even if it isn't, because they don't like the idea of anyone carrying any knives. Remember, DA's are law enforcement officers, they tend to not like people carrying knives.
I suggest that you take the time and seek out your local laws. If you are unable to find the specific laws in your city or county, my best advice is to contact a private attorney. They may charge you for the information, but since all they have to do, at most, is spend a few minutes doing research online to find the local laws, I don't imagine they would charge you a lot. Although they might charge you for a full hour.
What part of California are you in? I know that all of San Diego county (where I live) follows the California state laws.