The pilot was landing his tailwheel-equipped airplane on a rough and uneven, gravel covered, off-airport landing site adjacent to a river. Prior to landing, the pilot overflew the landing site multiple times at different altitudes for inspection. During the landing rollout the right wing struck tree branches, which resulted in a ground-loop. The airplane sustained substantial damage to the wings, empennage and left horizontal stabilizer. The pilot stated that there were no preaccident mechanical anomalies with the airplane that would have precluded normal operation. In the recommendation section of the NTSB Accident/Incident Reporting Form 6120.1, the pilot stated that the accident may have been prevented if he would have increased his familiarization of off-airport operations, or selected a more suitable landing site.