On April 15, 2000, at 1119 hours Pacific daylight time, an amateur-built Smith RV-4, N63SM, made an off-airport forced landing after experiencing an elevator control problem in cruise flight near Willows, California. The airplane, owned and operated by the commercial pilot, under the provisions of 14 CFR Part 91, sustained substantial damage. The pilot and passenger suffered minor injuries. The personal flight originated from Lincoln, California, about 1045, and was en route to Willows. Visual meteorological conditions prevailed and no flight plan was filed. The pilot reported that the passenger had been flying the airplane from the backseat, and about 8 miles south of Willows, the passenger informed him that he had no fore or aft control authority. The pilot took the controls and confirmed that there was no elevator response from the stick but that he did have control continuity to the ailerons. The pilot stated that he planned to land using the manipulation of aircraft trim and throttle as a means of controlling the aircraft's pitch attitude. In an effort to avoid making any major heading changes, the pilot attempted to land on closed runway 30 because of his present near alignment with the runway. Due to the lack of control authority to the elevator, the pilot attempted to gain altitude by trimming the airplane in the full aft position. Due to insufficient altitude to make the airport, the pilot reduced the throttle and mixture controls and landed in a rice field about 1 mile south of the airport, coming to rest in an upright position. The pilot reported that he constructed the airplane in 1985, and had flown the airplane 22 hours since the last condition inspection on April 3, 2000. The pilot reported that he had made some adjustments to the elevator control rods about 29 days prior to the accident. A Federal Aviation Administration inspector from the Sacramento Flight Standards District Office examined the airplane following recovery. He reported that the rear jam nut on the elevator push rod had worked loose, allowing the push rod to rotate off the forward connection. He stated that the jam nut and control rod were improperly installed.