The certificated commercial pilot, with one passenger aboard, was landing on a remote gravel-covered beach. During the initial touchdown, the left main wheel struck a large rock, and the airplane veered to the left. The pilot was able to correct for the veer, and brought the airplane to a stop. A postlanding inspection revealed substantial damage to the fuselage at the left main landing gear attach point, and the left door post assembly. The pilot said that there were no preaccident mechanical anomalies with the airplane.