On July 3, 2020, about 0722 mountain daylight time, a Cessna 172 airplane, N6929H, was destroyed when it was involved in an accident near Alpine, Utah. The pilot and three passengers sustained fatal injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. Radar data revealed that the airplane departed at 0637 from South Valley Regional Airport (U42) Salt Lake City, Utah, on a southerly heading. The airplane continued flying south and climbed to an altitude of about 5,500 feet. About 0642, it made a right 360º turn, then continued flying south, eventually climbing to an altitude of about 6,200 feet, around the western edge of Utah Lake. About 0702, the airplane made a left turn and began flying in a northeast direction, across Utah Lake. The airplane climbed as it crossed the lake and reached an altitude of 7,100 feet as it flew over the eastern edge of the lake. At 0712 and an altitude of approximately 8,000 feet, the airplane made a slight left turn to a northern heading. It continued to climb until it was lost off radar at 0714 at an altitude of 8,250 feet. The airplane reappeared on radar at 0718 at 8,785 feet on a northeast heading. It continued for about another minute and then made a right 270º turn, before disappearing from radar about 0722 on a west/northwest heading, at an altitude of 8,800 feet. A witness located near the accident site observed the airplane approach a canyon headed in a northwest direction. The witness noted that he thought the airplane was too low to clear the terrain and depart the canyon. He observed the airplane enter a “tight, right banking turn” in the canyon. The airplane leveled off after turning about 180º, followed by a couple of left and right wing-tip oscillations before it entered a clockwise, corkscrew spin. The airplane made about 1 1/2 - 2 rotations before it disappeared from the witness's line of sight in a vertical, nose-down attitude. The witness reported that the airplane’s engine was producing the same, constant sound until it started to vertically descend, and the noise started to oscillate. First responders to the accident site reported all components of the airplane were contained within about 100 feet of the main wreckage. Additionally, there was no smell of fuel at the accident site and the wing tanks appeared dry. Hydraulic deformation was observed to both wing tanks. A postaccident examination of the engine revealed the crankshaft was able to freely and easily rotate in both directions. Thumb compression and valve train continuity was confirmed on all four cylinders. The propeller was separated at the crankshaft flange, which exhibited torsional overload signatures consistent with the absorption of rotational energy. Additionally, one of the propeller blades displayed significant leading-edge gouging, torsional twisting, and chordwise striations across the cambered surface, as well as trailing edge “S” bending. No evidence of pre-impact mechanical anomalies was observed. An autopsy was performed on the pilot and front-seat passenger, by the Utah Department of Health, Office of the Medical Examiner. The cause of death for both was blunt force injuries. Toxicology testing was performed on the pilot by the FAA Forensic Sciences Laboratory. The testing was negative for ethanol and other drugs.