On July 23, 2006, about 0745 Pacific daylight time, a Grumman-Schweizer G-164B, N8376K, sustained substantial damage when it collided with terrain while maneuvering near Lamont, Washington. The commercial pilot, the sole occupant, received minor injuries. The airplane was registered to and operated by Moore Aircraft Company of Ritzville, Washington. Visual meteorological conditions prevailed for the 14 CFR Part 137 local agricultural application flight and no flight plan was filed. The flight originated from Pru Field Airport in Ritzville about 0715. The pilot reported that he was spraying a field adjacent to a set of hills, which required him to maneuver over the hills. While turning, he "misjudged the height of the hills at one point." He did not maintain terrain clearance, and the airplane impacted the ground.