A trailer carrying 6,900 gallons of fuel overturned near the northbound State Route 14 onramp at Sand Canyon Road, causing a hard closure in the area on Friday, according to a California Highway Patrol Newhall-area Office official.   The incident was first reported at approximately 9:26 a.m., said Carlos Burgos-Lopez, a spokesman for the CHP Newhall office, and added that on arrival officers were told the trailer was carrying a large amount of