The pilot reported that the airplane encountered “extreme” turbulence while on the approach to an intermediate stopover airport during a night cross-country flight. The pilot extended the downwind leg of the traffic pattern to stabilize the airplane, and during the base leg turn, the airplane struck a wire and subsequently impacted terrain. The airplane sustained substantial damage to both wings and fuselage. The airport is located at an elevation of 246 ft mean sea level (msl) in a major river gorge. The northern ridge line above the airport is about 2,900 ft msl, and the southern ridge line is about 1,300 ft msl. The accident location is located about 2 miles south of the airport at an estimated evaluation of about 650 ft msl. High tension powerlines are positioned south of the airport along the southern ridge. According to the United States Navy Observatory, the official sunset was at 17:12 Pacific daylight time (PDT), the official end of civil twilight was at 17:42 PDT and the official moon set was at 20:02 PDT. The night cross-county training flight was part of the pilot’s training curriculum for her commercial, airplane single engine land certificate. The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation.