On September 28, 2000, approximately 1545 Pacific daylight time, a Cessna 172K, N84034, experienced a partial propeller blade separation while in a climb near Burns, Oregon. The private pilot, who was the sole occupant, was not injured, and the aircraft, which was owned and operated by the pilot, received no other damage during the forced landing that followed the separation. The 14 CFR Part 91 personal pleasure flight, which departed Burns Airport about 15 minutes prior to the blade separation, was en route to Aurora State Airport, Aurora, Oregon. The flight was being conducted in visual meteorological conditions. No flight plan had been filed. There was no report of an ELT activation. According to the pilot, while nearing the top of a climb to 12,500 feet, and flying in an area of clear air turbulence, the aircraft's engine began to vibrate violently. He immediately shut the engine off by pulling the mixture to full-lean, and descended to an open field about 10 miles northwest of Burns. After a successful forced landing, the pilot discovered that a five-inch section was missing from the tip of one propeller blade. The remaining portion of the blade (inboard) was shipped to the NTSB Materials Laboratory Division. There it was determined that the separation occurred at a location where a fatigue crack had developed across approximately two-thirds of the cross section of the blade. The fatigue crack initiated at a damaged area where the leading edge of the blade had impacted a foreign object. The depth of the damaged area was about 0.05 of an inch.