Better double check that. I'm relatively certain that California requires handguns must be locked in a case and separated from the ammo, whether in the trunk or not.
Straight from the attorney general's website (which in general is slightly more restrictive than the actual law) and also the case if you read the statutes.
http://ag.ca.gov/firearms/travel.php
"California Penal Code section 12025 does not prevent a citizen of the United States over 18 years of age who is not lawfully prohibited from firearm possession, and who resides or is temporarily in California, from transporting by motor vehicle any pistol, revolver, or other firearm capable of being concealed upon the person provided the firearm is unloaded and stored in a locked container.
The term "locked container" means a secure container which is fully enclosed and locked by a padlock, key lock, combination lock, or similar locking device.
This includes the trunk of a motor vehicle, but does not include the utility or glove compartment. For more information, refer to California Penal Code Section 12026.1."
The trunk qualifies as a locked container under CA law. So it still has to be in a locked container for transport, but the trunk itself is considered a locked container and an additional locked container is not necessary.
Further open carry of an unloaded firearm is technicaly legal. So transport without a case in a locked trunk, and then transport openly from the trunk to the outdoor shooting would be legal, but not advised in a public setting.
The ammunition can be anywhere you want. Even with the firearm. It just cannot be 'attached to the firearm' or loaded into the firearm. As a precation people usualy keep it seperate. That is not a legal requirement.
(Case law even considers a side saddle attached to the firearm with ammo in it unloaded for that definition.)