The California Labor board is extremely employee friendly. Employers are required to pay terminated employees all owed wages within three days of termination in CA. Failure to do so will result in serious penalties to the employer.

Recommendation:
1. Demand payment in full immediately (or within two days or something like that), and do so in writing. Tell them that if they don't, you'll take this to the labor board. Their counsel should understand the consequences of you doing so. Note: you are not required to sign anything or release them from any other claims in order to get your check, by law.
2. If they don't, call up the labor board in your city. Explain what happened, and work with whatever agent is assigned to your case to get it resolved.

Good luck!