On March 15, 1997, at 1815 mountain standard time, a Piper PA-28R-201T, N38703, was destroyed when it struck a fence during a forced landing near Hartsel, Colorado. The private pilot and one passenger were not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the personal flight conducted under Title 14 CFR Part 91. The local flight originated at Watkins, Colorado, approximately 1800. The following is based on telephone conversations with, and the written accident report submitted by, the pilot. He said it was shortly after sunset and he was in cruise flight at 16,500 feet msl when oil began to appear on the windshield. He retarded the throttle to idle, then slowly added some power. He did not notice "any substantial response" from the engine, but did observe more oil on the windshield. He slowed the airplane to 100 knots, then determined that the nearest airport, Buena Vista, was about 21 miles away. He did not believe he would be able to fly to Buena Vista, and elected to land on a dirt road. He said approach speed was 10 knots higher than normal "to avoid obstructions," and he did not use flaps "because I would not have made it to the road." He soon realized, however, that he was going too fast and would overshoot the road, so he turned towards an adjoining field. He maneuvered the airplane over a herd of buffalo and touched down. During the landing roll the airplane struck a fence, rupturing the right wing fuel tank. Fire department personnel later discovered the oil filler cap was missing. The airplane was examined at Beegles Aircraft Service in Greeley, Colorado. The access panel was opened and the dipstick was removed. It registered 3 quarts of oil. The pilot said he "thoroughly preflighted the airplane" and checked the oil. The oil level was "about one-third down from the top" (about 6 quarts; capacity is 8 quarts). The oil filler cap is located next to and behind the dipstick. The pilot said the oil filler cap "was easily visible and in place," but he did not physically check it for security. The oil filler cap was eventually located in a recess atop the right bank of cylinders where it had fallen.