On September 19, 2000, about 1235 hours Pacific daylight time, a Bell 206BIII, N90214, was substantially damaged while attempting to takeoff from a ridgeline near Ojai, California. Aspen Helicopters, Inc., operated the helicopter under the provisions of 14 CFR Part 135. The commercial pilot was not injured; two passengers sustained serious injuries. The local charter flight departed Oxnard about 1110. Visual meteorological conditions prevailed and a company VFR flight plan was filed. The accident coordinates were 34 degrees 30.3 minutes north latitude and 119 degrees 08.3 minutes west longitude. The pilot stated he was flying personnel to several flood control monitoring stations. One station was visited and an effort to visit a second was terminated after three attempts to land were made. This was the third station they visited, and its elevation was about 5,000 feet. After landing to the west on a ridgeline, the pilot decided to reposition closer to the station. He later determined the winds were 240 at 5 knots. He hover taxied to his landing area. As the skids touched down, the pilot felt the helicopter slide to the right. He picked back up into a hover and decided to fly back to the original landing site. After applying takeoff power, he pushed the nose of the helicopter over and began to fly away downslope. The nose of the helicopter began to rotate to the right, even with full left pedal applied. The pilot reduced collective and continued downslope. As the nose continued to the right, he increased collective, and began to follow the right yaw with cyclic. He flew the helicopter to a downwind position approximately abeam his landing site. Then the nose tucked down and the tail swung to the left. He reduced collective and throttle as the helicopter crash-landed into the slope below his landing site. The Federal Aviation Administration accident coordinator flew by the site and noted the air temperature was 85 degrees Fahrenheit and computed the density altitude to be about 8,000 feet.