MASHPEE — Two teenagers were flown by medical helicopters to a Boston area trauma center after their car crashed into a boulder in Mashpee, according to police and fire officials. Police were called at about 8:29 p.m. Friday to the area of 80 Echo Road, Police Chief Scott Carline said in a statement. The car was traveling westbound on the road when it struck the rock, he said. The boulder was as big as the car, and probably weighed more than the car, Mashpee Fire Chief Thomas Rullo said Saturday morning. The car hit the boulder straight on with very little stopping power, he said.