dude this sucks but you can beat it first the lab will test it and if it is not a narcotics then they will see what it is, but first like you said it is a community car so other have access to it and they also give people rides..
remember they have to prove that it belonged to you and with that many people in your car that is going to be hard to do.....it will be dropped I am almost sure...do not talk to them and wait for the lab results to come back and see where you stand it could be dropped then...if not in court they have to prove it belonged to you and I just dont see that happening..with the information given....
I dont know about cal....but had the same thing happen with me several years back and it got dropped because they cant prove I knew about it....cal is very liberal so you should be good to go..