What are the Medical Marijuana growing rules in California?

My neighbor is growing over 80 marijuana plants in the field behind his house. Everyone can see them, the entire neighborhood now knows what he’s up to and he has a hokey fence around them. He claims to be growing for a cannabis club and they are leasing his land. I thought there was a limit a person could grow? I’m not against medical marijuana its just that when someone is growing a field of plants which could bring in thousands of dollars.. (he says 100K) the criminal element will start to come around to rip him off and most likely use violence if necessary. Can someone tell me what the rules are in California? Let the debate begin! This should stir some very interesting responses and comments! 🙂