The solo airline transport pilot was landing on a beach when the airplane struck a rock, resulting in a nose over and separation of the right main landing gear. The airplane sustained substantial damage to the right wing during the accident sequence. The pilot made a low pass over the landing area, and thought it looked suitable for landing. Upon landing, he said the rocks on the beach were larger than they appeared from the air, and he inadvertently struck one. The pilot said there were no known mechanical problems with the airplane prior to the accident. In a written statement to the NTSB, the pilot said he should have picked a better place to land.