Legal Question in Criminal Law in California

If police find contraband while executing a search warrant they are entitled to seize it. They need not turn a blind eye to evidence of any crime. At the same time, when they execute the warrant they must conduct the search in a manner that is reasonably designed only to locate the items it specifies. If the warrant specified only large electronics, for example, the police had no right to search the pockets of clothing in your dresser drawers.

If your marijuana was located someplace where the police just happened upon it in the course of a proper search, then they were allowed to seize it. If they found it someplace they shouldn't have been searching, then they weren't.

If they took it from your house, they should have listed it in their inventory of items seized. I'm not sure you should complain that they didn't. If it isn't in the inventory, you may not be charged for possessing it. (Depending upon how much there was, the charge might even be possession with intent to distribute.) And even if they do charge you with possession, the fact that it isn't listed in the inventory will make it easy for your lawyer to argue that there is at least a reasonable doubt about whether you actually had it.

Unless you had this marijuana pursuant to a valid prescription and had a valid medical marijuana user permit at the time, you should probably just let the matter go. The only alternative is to tell the police that you had marijuana in the house, which would be admitting to a crime. That's a good way to get yourself charged even if you weren't otherwise going to face charges. And since possession of marijuana without a medical use card is illegal, there's not much chance the police would give it back to you anyway.