To answer your question specifically, you could spend up to one full year in prison for owning mushroom spores. You could also suffer the permanent revocation of your drivers license.But, to get to the more interesting side of this... why do you think they created the law, and has it ever been enforced?
My understanding of this is that the reason they came up with the law is to discourage spore sellers in California. Which is exactly what ended up happening, there are no spore sellers in california any more. However, to my knowledge no one has ever been tried, convicted, and sent to prison for this offense. It has been used to force people to do certain things, like stop selling spores, but thats about it. So don't worry, what you should worry about is the production charge, which could land your ass in jail for a much longer period of time.