Before takeoff the pilot failed to verify that the main cabin door was closed and latched. After takeoff the door opened and he maneuvered the airplane to land in the opposite direction than for takeoff. He stated that he became distracted due to the perceived emergency and landed about 6 feet short of the runway on upsloping terrain. The left main landing gear then separated from the airplane which bounced onto then off the runway into a 25-foot deep ravine where the airplane came to rest upright.