The pilot reported that he had recently purchased the airplane and while flying through mountainous terrain, he mistakenly flew the airplane into a boxed canyon. He felt that the bigger engine would help the airplane climb over the mountains. He noticed the terrain was rising faster than expected but was unable to turn around due constrictive terrain. Realizing the airplane was not going to clear the ridge and concerned the airplane would stall if he attempted to turn around in the narrow pass, he looked for an area to make an off-airport landing. The pilot noticed an area that had a tree and elected to use the tree to take the brunt of the impact during landing. He reduced the airspeed and impacted the tree, which resulted in substantial damage to the left wing and fuselage. Additionally, the pilot reported that he was seated in the rear seat of the airplane and was not able to lean the engine due to the fuel mixture controls being located in the front seat of the airplane. He believed that the combination of high altitude and the inability to lean the airplane’s engine, degraded the airplane’s performance. The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation. Postaccident site examination by local law enforcement revealed that the airplane impacted rugged, remote, mountainous terrain at an elevation 11,200 ft mean sea level (msl). The calculated density altitude was about 12,500 ft.