The 22 year old pilot and his three passengers departed on a three day excursion of Bryce and the Grand Canyon. The pilot had logged about 72 hours of flight time. The rented aircraft departed at night 68 pounds over gross and 1 inch aft of the most rearward allowable C.G. limit. After reaching their first destination and spending the day sightseeing, they departed again at night for the Grand Canyon. The weather was marginal with snow showers. The planned 56 minute leg was tracked on radar for a total of 1 hour and 39 minutes, a meandering and undulating track up to 13,400 feet MSL was recorded. The aircraft departed with 1 hour and 40 minutes of fuel in each tank. At the accident site the right tank was full and the left tank was empty. The fuel selector was on the left tank. The aircraft impacted mountainous terrain at about 7,000 feet MSL in a flat spin.