Construction Battalion Maintenance Unit 303, San Diego is working to reconstruct the San Mateo Live-Fire Training Convoy Course on Marine Corps Base Camp Pendleton, May 17. One and a half mile of this five-mile long training course has a six percent grade, making it one of the steepest roads on base. Extreme erosion due to heavy rain and excessive use made this road increasingly perilous to navigate. - Construction Battalion Maintenance Unit 303, San Diego is working to reconstruct the San Mateo Live-Fire Training Convoy Course on Marine Corps Base Camp Pendleton, May 17. One and a half mile of this five-mile long training course has a six percent grade, making it one of the steepest roads on base. Extreme erosion due to heavy rain and excessive use made this road increasingly perilous to navigate.