On July 19, 2004, at 1005 Pacific daylight time, an experimental Root RV-4, N901ER, registered to and operated by the pilot as a 14 CFR Part 91 personal flight, experienced a loss of engine power shortly after takeoff from Cawleys South Prairie private airstrip, Buckley, Washington. During the off airport forced landing, the aircraft stalled and landed hard in an open field. Visual meteorological conditions prevailed at the time and no flight plan was filed. The aircraft was substantially damaged and the private pilot, the sole occupant, was seriously injured. The pilot reported to a family member that he was taking the aircraft to Puyallup, Washington, for a maintenance visit. Shortly after takeoff to the south, the engine lost power. The pilot attempted to briefly trouble shoot the problem, but due to the lack of altitude opted to commit to an off airport landing to an open field. In an attempt to avoid trees and maneuver to the field, the pilot reported that the aircraft stalled. In a conversation with the pilot's son on July 23, 2004, the son reported that his father stated that "I knew I had exhausted the left tank the night before. I just forgot to switch to the fullest tank that day." The pilot reported that he had departed with the left fuel tank selected. Inspection of the engine by investigators from the National Transportation Safety Board and the Federal Aviation Administration on July 23, 2004, it was determined that no mechanical failure or malfunction of the engine was noted. The right fuel tank had been compromised and fuel stains were present. It could not be determined if the left fuel tank had been compromised, however, no fuel stains were noted. No fuel was observed when the fuel sumps on either tank were opened. No fuel was present in the fuel gascolator or fuel bowl.