The topic of transporting firearms in California is a very broad one, and there are a lot of up-to-date sites which are covering it in depth. I feel there's little reason to create yet another guide, but I will add the following point - which has been difficult to locate a citation for.
Per CPC 26405 as of 8/8/2016, a firearm other than a handgun (i.e. shotgun, long gun, Title 1 firearm, AOW, etc) may be transported in either a locked container, or while legally "encased". The referenced "section 26400" is the prohibition on unloaded open carry.
Section 26400 does not apply to, or affect, the carrying of an unloaded firearm that is not a handgun in any of the following circumstances:
(c) When the firearm is either in a locked container or encased and it is being transported directly between places where a person is not prohibited from possessing that firearm and the course of travel shall include only those deviations between authorized locations as are reasonably necessary under the circumstances.
The definition of "encased" is below:
Per CPC 16505 as of 8/8/2016:
16505. For purposes of Chapter 7 (commencing with Section 26400) of
Division 5 of Title 4, a firearm is "encased" when that firearm is
enclosed in a case that is expressly made for the purpose of
containing a firearm and that is completely zipped, snapped, buckled,
tied, or otherwise fastened with no part of that firearm exposed.
-- Sean Newton - 08 Aug 2016