The pilot said he was attempting to land a tailwheel-equipped airplane at an off-airport site, which was surrounded by higher terrain on all sides. Before beginning his approach, the pilot determined the wind conditions and then planned an approach into a 10-knot headwind. He said that, while on final approach to the site, he "side-slipped" the airplane to steepen the approach, and a sudden wind shift caused the airplane to descend faster than anticipated. He was unable to arrest the descent, and the airplane's main landing gear wheels collided with a mound about 150 feet short of the intended touchdown point. The airplane bounced as the pilot added engine power to cushion the landing, and as it touched down again, the main landing gear collapsed. The airplane sustained substantial damage to the wings and fuselage. The pilot reported that there were no preaccident mechanical anomalies with the airplane.