That is not a fair comparison. California's gas tax (including excise tax) is higher than Oregon. In addition, California requires a more expensive blend of gas

That is not a fair comparison. California's gas tax (including excise tax) is higher than Oregon. In addition, California requires a more expensive blend of gasoline. A better comparison would be to a state that has similar taxes and gasoline requirements. As a bonus, the availability of refineries is a significant factor in gasoline prices.