The pilot reported that during the landing on the unimproved mountain airstrip, he did not apply the brakes as he intended to “coast” up to the end of the runway, and then depart in the opposite direction, downhill. The pilot did not identify the end of the runway until the last moment when he applied the brakes and full right rudder. However, the airplane exited the runway, and impacted a ditch resulting in the collapse of the left main landing gear. The pilot stated that he had identified the red runway end marker in the air, but could not see it in the tall grass until it was too late. The airplane sustained substantial damage to the left main landing gear assembly. The pilot reported no mechanical anomalies with the airplane or flight control system.