On September 18, 2006, about 0800 Pacific daylight time, a Bell 47G, N7762, landed hard on uneven terrain and rolled over near Angels Camp, California. Arrow Aviation, d.b.a. Gunner Aviation, operated the helicopter under the provisions of 14 CFR Part 91 as an aerial observation flight. The helicopter sustained substantial damage. The commercial helicopter pilot and one passenger were not injured. Visual meteorological conditions prevailed for the flight that departed Rancho Murieta, California, about 0615. The helicopter came to rest at global positioning system (GPS) coordinates of 38 degrees 1 minute north latitude and 120 degrees 28 minutes west longitude. In the pilot's written statement to the National Transportation Safety Board, he indicated that they had been flying for about 2 hours, just east of Angels Camp, and planning on returning to RIU. He reported that both he and his passenger need to use a restroom. He knew it would be 20 minutes to Calaveras Airport, or 50 minutes to RIU, and decided to land so that he would be better able to focus on the return flight to RIU. The pilot chose to land on a flat clear-cut plateau near a local vineyard. The plateau was 100 feet by 200 feet. The area that he determined would be used for the approach had two trees that were at least 50 feet apart, which would give him sufficient clearance to fly between them. He also noted that at the approach end was a 6-foot-high mound, followed by a 2-foot hole, and another 2-foot mound; all were about 10 feet in diameter, with the remainder of the area as flat with no additional obstacles. The pilot reported that he began a steep approach into the wind. The helicopter was about 50 feet from the end of the plateau when the wind shifted, which created a tail wind condition. The airspeed dropped below ETL (effective translational lift) that resulted in a loss of lift. The loss of lift altered the angle of the approach from a flat landing area to an approach that was on the downslope of the plateau. The pilot pushed the cyclic forward to gain forward airspeed, and applied collective and power to avoid contacting the slope of the plateau. After performing this maneuver, the helicopter was above the level of the plateau; however, it did not put the helicopter above the 6-foot mound. He flared the helicopter to gain additional altitude then leveled the helicopter as it approached the mound. As the helicopter passed over the mound, the tail rotor guard struck the top of the mound, which forced the nose of the helicopter in a downward attitude. The landing gear skid collided with the 2-foot mound and the tailboom broke off. The helicopter began to yaw to the right and roll to the left. The helicopter cleared the 2-foot mound, and came to rest about 5 feet from the mound, lying on its side.