On June 17, 2011, about 1640 Pacific daylight time, a DeHavilland Beaver DHC-2 MK 3, N260HC, landed hard on the runway at a private airstrip near Jefferson, Oregon. The pilot/owner operated the airplane under the provisions of 14 Code of Federal Regulations Part 91 as a business flight. The pilot, the sole occupant, was not injured. The airplane sustained substantial damage to one wing and the pontoon/landing gear. Visual meteorological conditions prevailed for the local area flight, and no flight plan had been filed.The pilot reported to the National Transportation Safety Board investigator-in-charge (IIC), that the runway sits on a plateau. He stated that his approach was normal, but on short final, the airplane experienced a thermal lift then a downdraft, which dropped the airplane. He added power, however, there was not sufficient time to arrest the sink rate before the airplane landed hard. The pilot reported no preimpact mechanical malfunctions or failures with the airplane or engine that would have precluded normal operation.