Been gone over a bunch in other threads.
People vs Clark (1996) is the applicable case law which found that the ammo has to be in a position where it can be fired (paraphasing). Case invloved a shotgun with ammo in a side shell holder attached to the gun, dude was popped for a loaded gun, but the court found that it wasn't loaded even with the ammo attached to the gun in that manner and went into more detail as to what "loaded" actually means as far as transporting your gun around legally.
Another easy place to point people though is the CHP's FAQ web page:
Originally Posted by CHP Website FAQ Page
I will be traveling to California and want to carry my weapon. I currently have a concealed weapon permit. How can I legally transport my weapon while driving through the state?
California law does not recognize concealed weapon permits from other states; therefore, they would not be held valid. If you wish to transport a handgun during your California visit, it should be carried unloaded in a locked container. In the absence of a suitable container, you may secure the unloaded handgun in the locked trunk of a passenger car. Ammunition may be kept in the same container or trunk, but the handgun must remain unloaded with no rounds in the cylinder and no loaded magazines in the magazine well.