The state portion of the gas tax is between 30-40 cents/gallon depending on where you are (sales tax fiddles). Without that, you wouldn't have roads to drive on for very long (maintenance and operational projects would go away). Yes, there's also an effect due to cap n trade, fuel formulation, etc. - most economists add it up to around $1/gallon that's a justifiable difference between CA gas and elsewhere in the US. Current difference is near $2/gallon. How exactly it gets there is a mystery.