On September 16, 2022, about 1630 Pacific daylight time, a Cessna 172L, N7917G, was substantially damaged when it was involved in an accident near Ventura, California. The pilot was not injured and both passengers sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that, while enroute about 2,000 ft mean sea level (msl), he heard a "pop" followed by a partial loss of engine power. The airframe started shaking badly, he pulled power to idle, established best glide, and contacted Air Traffic Control (ATC). ATC provided alternate airports and current weather information. Unable to maintain altitude, he initiated a forced landing to a clearing on the beach. During the landing roll, the airplane impacted a rock retaining wall. Postaccident examination of the airplane revealed that the left wing and forward fuselage were substantially damaged. Subsequent lighted borescope examination of the airplane’s engine revealed mechanical damage to the No. 4 cylinder’s combustion dome and piston face. The Nos. 3 and 4 cylinders were removed. Metallic debris was observed obstructing the No. 3 cylinder intake valve. The No. 4 cylinder was removed, and remnants of the exhaust valve were observed within the cylinder. The No. 4 cylinder and remnants of the No. 4 exhaust valve were sent to National Transportation Safety Board Materials Laboratory, Washington, DC, for examination. The examination of the fracture surface of the No. 4 exhaust valve revealed characteristics consistent with a fatigue fracture. Review of maintenance records did not reveal any recent maintenance performed on the cylinder.