The pilot reported that he was conducting a wildlife survey flight and had been airborne about 2.5 hours, when the observer said that he would like to take a break. At that time, the flight was over a high mesa covered in short grass, which the pilot decided was a suitable landing area. The touchdown was smooth, but the airplane encountered undulating terrain during the rollout and began to bounce. The pilot added full power to abort the landing, and the airplane's speed began to increase; however, the pilot was unable to take off before impacting a bush. The airplane traveled several hundred feet down a ravine and came to an abrupt stop. The airplane's main landing gear collapsed, and both wings sustained substantial damage. The pilot estimated that the density altitude at the landing site was about 8,950 feet. He stated that the accident could have been avoided had he "made the decision not to land off-airport in that area at such density altitudes." The pilot reported no preimpact mechanical malfunctions or failures with the airplane that would have precluded normal operation.