N4646A

The pilot reported that he landed on the unimproved dirt airstrip and came to a full stop. He began taxiing and started to turn around when he encountered a washed out area. The pilot stated that after proceeding about another 30 feet the left main landing gear collapsed through an eroded section of the dirt airstrip, which was not visible to him. The pilot reported that the landing gear fell about 2 feet followed by the airplane going up on its nose and the propeller striking the ground; the airplane subsequently fell back on its tailwheel. The pilot reported substantial damage to the airplane as a result of the left main landing gear strut being bent and damage to the left gear attachment structure.