The aircraft was landed at the McKenzie Bridge State Airport where two passengers deplaned. The airport had a 2600 ft turf runway with an upslope gradient of 3.4% toward the east. The Airport/Facility Directory stated, "Unattended. Land to E, takeoff to W. Caution - owner advises contact with State Aeronautics Div. (503-378-4880) prior to use." A sign at the east end stated "Warning - takeoff at this end only," while a sign at the west end stated, "Warning - takeoff not recommended from this end." The elevation was 1620 ft. At a ranger station (1.5 mi west) the temperature was 87 deg and the wind was from the southwest at 6 mph. A Forest Service official estimated the wind was mph higher at the airport. During takeoff on runway 06, the aircraft collided with trees about 15 yards from the departure end, about 20 ft AGL. It came to rest and burned about 30 yards from the runway. No preimpact malfunction or failure was found during an on-site investigation or a subsequent engine teardown.