The pilot stated that he was attempting to fly through a narrow mountain pass when he realized that the clouds were obscuring the top of the pass. He decided that the pass was too narrow to turn around, so he elected to land the airplane on a gravel access road. During the landing roll the airplane hit a ditch, veered to the left, and impacted terrain. The airplane sustained substantial damage to the left wing. The pilot reported that there were no preaccident mechanical anomalies with the airplane.