On June 16, 2007, about 1030 Pacific daylight time, a Piper PA-12, N2343M, collided with a rock on the landing roll on a dirt airstrip near Imnaha, Oregon. The pilot was operating the airplane under the provisions of 14 CFR Part 91. The commercial pilot and one passenger were not injured; the airplane sustained substantial damage. The cross-country personal flight departed Lewiston-Nez Perce County Airport, Lewiston, Idaho, about 0950. Visual meteorological conditions prevailed, and no flight plan had been filed. The pilot stated in a written report that he was attempting to land at Sluice Creek, a back country dirt airstrip located along the banks of the Snake River in Oregon. During the landing roll, the left tire struck a rock and the airplane departed the runway to the left. The tires had been inflated to 25 pounds per square inch (psi) before the flight. He noted that on previous flights to Sluice Creek he had deflated the tire pressure to 12-15 psi, and landed without incident. According to an FAA inspector, the airplane sustained substantial damage, including a bent wing strut, which the pilot temporarily repaired at the scene of the accident.