The pilot was landing a tailwheel-equipped airplane on a soft tidal beach. Prior to the accident, the pilot circled the beach at approximately 700 feet above ground level, and thought it looked suitable for landing. During a second low pass, he allowed the main wheels and tailwheel to touch down to determine how soft the surface was, and he believed the surface appeared firm. During the landing roll, the main landing gear contacted an area of soft sand, and the airplane nosed over, resulting in substantial damage to the left lift strut and rudder. The pilot indicated that there were no preaccident mechanical anomalies that would have precluded normal operation.