Obviously there are going to be many differences in California and Alabama. California is quit arguably the most liberal state in America while Alabama is arguably the most conservative. My time in Los Angeles has been short so I have not picked up on too many cultural differences but I will gladly tell you a few.
The first thing that I noticed is that people out here are much more outgoing, not necessarily friendlier, just more outgoing. In Alabama we kind of have an unwritten rule not to talk to any strangers, we will smile at you all day long but we tend to keep to ourselves. We stand in the checkout lines and use the urinal rule (Ladies, this rule is head straight forward, no eye contact and no talking.) We just patiently wait our turn to be checked out. We only talk to each other when things are not going according to plan; the cashier is new, the barcode is messed up, or someone is wanting to pay in dimes and nickels. Then we turn to one another and make little comments to make light of the situation. People in Los Angeles will just start up a conversation for no reason. I kid you not, my roommate and I were walking down the body wash aisle. Out of nowhere a woman, who was on the phone, stuck a bottle in our faces and told us to smell how incredible it was. I may have glared at her a little rudely for breaking the our rule. Other times I have been standing in line with someone carrying on a conversation and had other people chime in on it. Oh, and one of my very first shopping experience in California was in Target. I was wearing a red Alabama shirt and a complete stranger stopped me and told how I should not be wearing that shirt. At first I was taken aback and ready to get in an argument with this stranger about how awesome Alabama is. She proceeded in telling me how she made the mistake of wearing a red shirt to Target once and everyone kept stopping her to ask her questions because it appeared she worked there. I guess when you live in a such a populated area you cannot avoid people and at some point you just give in and start talking to strangers.
Diversity is another huge difference that you will quickly pick up on. People of all races and nationalities live in California, and many have grown up here. This can be seen everywhere. Los Angeles has parts of town that are official known as Little Armenia, Little Tokyo and Koreatown. You will get into some of these areas where billboards and signs will no longer be in English. Church has been another place where I have seen diversity. Sadly, in Alabama (and the majority of the south) our churches are normally segregated and not for malice reasons, they just are. Our given history I am sure plays a part in this, but anyone reading this not from Alabama, please know that we do not purposefully and maliciously segregate our churches. I have been to several churches out here and each one has been beautifully diverse. Worship is a completely different experience when you can look around the room and see God's people of different races praising the same Father. It is awesome and I believe a little glimpse of Heaven.
Those are the two big cultural differences that I have noticed. As I stay longer I will pick up on more. Currently I am learning that football is not a big deal, naturally they have the Pac 10, I would not care for football either. Religion is taboo here, the only time it is okay to talk about it is when you are saying how you do not like it. Northern California is more liberal while Southern California is more conservative, this is out of complete greed not morals like in the South. Alas, It is too early in the game for me to speak on these topics.