I'm not sure on this (I'll actually need a coast person to give a definate answer), but I think the coasts pay higher taxes on their gas than other places do.
I can't speak for other states, but California has high state and environmental taxes on its gas. I believe (but am not sure) that California also requires certain additives to make the fuel burn cleaner, and that impacts the price as well.
That and most Californians live in high density urban and suburban areas. Those areas are just more expensive for EVERYTHING.