OCMusicJunkie, you need to talk to a lawyer who is familiar with federal law on this issue as well as California and Minnesota state law. This is not just an issue of state law, you may be considered a prohibited person (with no rights to possess a firearm EVER) under federal law in several appellate jurisdictions depending on the facts of the case. It is a really narrow, poorly understood area of law that even a lot of attorneys are unclear on.
The short version is that under 18 USC 922(g) (prohibited persons) any person who has been adjudicated as a mental defective or has been committed to any mental institution may not possess or purchase firearms. A temporary commitment for observation of the type you describe is universally accepted as not being a commitment under this section. However, some appellate courts (and some lower state courts/state AGs) have taken that position that such a temporary commitment can count as "being adjudicated as a mental defective" depedning on the circumstances of the case.
Personally, I don't think the appellate cases holding this can survive review post-Heller; but you need to talk with a knowledgable attorney about the specifics of your case, particularly if you had any kind of hearing. You might contact the Calguns Foundation
and explain your situation to them. They may be able to recommend an attorney who can help you.