From DOJ web site http://ag.ca.gov/firearms/travel.php
SHOTGUNS AND RIFLES
Nonconcealable firearms (rifles and shotguns) are not generally covered within the provisions of California Penal Code section 12025 and therefore are not required to be transported in a locked container. However, as with any firearm, nonconcealable firearms must be unloaded while they are being transported. A rifle or shotgun that is defined as an assault weapon pursuant to Penal Code 12276 or 12276.1 must be transported in accordance with Penal Code section 12026.1.
So you could IMO transport long guns in a rack. BUT!!!!!
A "law update" video was circulated to California police departments in early 2007, notifying officers that the mere presence of a gun case in a vehicle constitutes a valid cause to open the case and inspect the weapon to verify that it is unloaded. You have no right to refuse search if a gun case is visible. This does not, however, mean that you must grant consent to search the rest of your vehicle, only the gun case. This information courtesy of eta34, from Calguns.
Based on the above. Why would you want the extra police attention?
I would love to smash around town with my AR, AK, and mossy 590 in the window of my truck! And I DO carry them with me just out of sight!
This is a quick response and by NO means is it legal advise. Just what I think and found in a short time.
Let us know how you make out!
"If squirt guns are outlawed, only outlaw squirts will have guns!"