The pilot reported that, during the landing roll in a tailwheel-equipped airplane on a remote airstrip, he encountered a depression in the landing surface, resulting in the separation of the left main wheel. The left main landing gear leg subsequently dug into the ground and folded back against the fuselage, which caused substantial damage to the fuselage near the main landing gear attach points. After exiting the airplane, the pilot observed that the left main gear leg had fractured above the axle bolts, and the tire, axle, and lower portion of the main landing gear spring had separated from the airplane. The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation. Photos of the fracture surfaces from the main landing gear spring were examined by the NTSB Materials Laboratory. The features observed were consistent with a fatigue fracture and corrosion. It is likely that a fatigue crack initiated due to corrosion damage at the fracture origin.