FRESNO, Calif. -- If you think California's gas prices are high now, they are about to get even worse.You may want to fill up your gas tank this weekend before prices start to go up on Monday.California will have the highest gas prices in the nation when new gas tax kicks on July 1.California's gas tax increases by nearly six cents per gallon to more than 60 cents per gallon, making it the highest in the nation.The increase is expected to generate nearly $54 billion in revenue over a decade.Last November, California voters rejected a statewide proposition to repeal the gas tax increase.