A 21-year-old Alabama woman was killed and her 6-month-old son was critically injured when her pickup collided with an 18-wheeler Friday near Canton. The accident shut down Ga. 20, just west of the city for about two hours, beginning at about 11:10 a.m., said Sgt. Jay Baker, spokesman for the Cherokee County Sheriff's Office. Initial reports indicate the pickup, heading west, crossed the center line and struck the eastbound 18-wheeler driven by Ronald Sims of Dahlonega, said Baker.