On February 20, 1999, about 1330 mountain standard time, a Piper J-5A, N28123, registered to and operated by the pilot as a 14 CFR 91 pleasure flight, was substantially damaged after colliding with power lines near Rexburg, Idaho. Day visual meteorological conditions prevailed and no flight plan was filed for the local flight. The private pilot was not injured. There was no fire and no report of an ELT actuating. The flight originated from the Rexburg-Madison County Airport, Rexburg, Idaho, approximately 30 minutes prior to the accident. During a telephone interview, the pilot stated that he struck a set of power lines while flying over a friend's house. The pilot stated he did not see the power lines until it was too late to avoid them. After striking the power lines, the pilot attempted to land in a nearby field, due to extensive damage to the aircraft's rudder. The aircraft's right main landing gear collapsed during the forced landing. The power lines were approximately 35 feet above the ground. The pilot reported no mechanical failure or malfunction with the aircraft prior to colliding with the power lines.