Why are gas prices so high in California?

OK, I may be really dumb, and this is a serious question, but tell me in what universe this makes sense? These are gas prices from across the country this week. In Simpsonville, South Carolina regular gas is $2.13. In Denver, Colorado, Regular gas is $2.70. And in Oceanside Harbor, California, Gas is a whopping $4.36!

Why are gas prices so high in California?

Even read this article - http://www.usnews.com/news/business/articles/2015/07/12/survey-us-gasoline-prices-down-2-cents-in-the-past-2-weeks that states "California sees prices at the pump spike amid national downward trend".  This asks the same question but the answer seem lame.