The pilot reported that during a cross-country flight he was unable to maintain a sufficient climb rate to clear the mountainous terrain, and he initiated an off airport precautionary landing to a nearby alpine meadow. When the airplane touched down, the left main landing gear collided with a large rock and collapsed. The airplane bounced and touched down a second time and slid approximately 150 feet to a stop. The airplane’s fuselage and under carriage sustained substantial damage during the accident sequence. The pilot reported no mechanical failures or malfunctions with the airframe or engine that would have precluded normal operations.