First what about Big Law Appeals to you?
Many people think Big Law is what they want only to find out it sucks. If you have worked in a Big-Law firm in some capacity or know Big-Law attorneys then you might have a reason, but if it is just the money you might want to rethink it.
Big Law is Kind of on the Way Out + NorthWestern or UC Irvine Might not get you in the door.
I don't know of any Big Law Firms really thriving right now. People are looking for ways to cut costs and the future of Big Law is not great at least in the near future it could change, but while your in school it probably wont. Even if the market increases Northwestern is a good school, but Harvard, Yale, win. Stanford, Berkeley, UCLA, USC will win in California. There are just plenty of excellent law schools in California so there is not much of a need to reach out to Northwestern for recruiting purposes. I am sure some firms do OCI for California positions in Northwestern, but I just don't see it making a lot of sense for them.
UC Irvine is probably going to be fine, but as the poster above said nobody knows how they will turn out. Clerkships all that happen, but I imagine only for the students in the top 10% at these schools and there is a 90% chance you won't be in the top 10%. Realistically the same thing applies for the Big Law positions you have to be at the top of your class and the odds are you won't be. Again this is no knock on you, but the students at these schools will be excellent and there is a 50% chance you will be in the bottom half of the class. If that is the case BigLaw/Clerkships probably won't be in the picture.
Realistically if you want to end up in California then go to law school in California. 3 years is a long time and you are going to get an apartment, probably a girlfriend/boyfriend, friends, a whole new life over those 3 years and it will be difficult to leave. Not only that you will be startled with 100k in debt if you go to Northwestern and you won't really be able to pick up and move to anywhere, but your parent's basement while getting started up in a new location. Of course if you get the Big Law Gig or Clerkship that won't happen, but be realistic there is a strong possibility you will not graduate Valedictorian and then what do you do?
if you really want to be in California then go to law school in California that is my two cents. I am sure there are other opinions out there. P.S. did you apply to schools like UCLA, USC, LMU, Pepperdine, Hastings. I would imagine those would open up more Big Law possibilities in California than Northwestern would. Northwestern would open more big law doors nationally, but if you really want to be in California then those schools would fair better.