The pilot reported that he overflew an open field that he intended to conduct an off airport landing on. He stated that the field was of sufficient length and had a suitable landing surface. During the landing, the tailwheel equipped airplane touched down longer than the pilot had intended and he intentionally ground looped the airplane to avoid traveling down a ravine. During the accident sequence, the left wing sustained substantial damage. The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation.